I hear and read mention of a "responsive frame". What does
this mean, and what kind of frame is responsive, and not?

--
Dieter Britz

On Friday, March 4, 2022 at 6:49:27 AM UTC-8, Dieter Britz wrote:
> I hear and read mention of a "responsive frame". What does
> this mean, and what kind of frame is responsive, and not?

Dieter, this is one of those terms that is invented to mean nearly anything.. Originally it meant the bike was responsive to lean and fork motion but it soon became an advertising term that means little if anything. Responsiveness as I've learned to my dismay is a combination of many things from the flexibility of the frame to the tire size and pressure. On a steep descent I discovered that my Colnago C40, because of the flexibility of the frame would steer itself. This was a bike very often described as responsive. This sort of self-steering over the years was worked out of steel frame with ultra-stiff steel tubing such as oversize and triple butting etc. But responsiveness is a product of the fork flex and tire/wheel give. So unless the frame is very flexible such as the C40, it has very little influence. And ultra stiff plastic structures can slowly break themselves up.

So I always remember that although they are not supposed to, Carbon fiber frames have a finite lifespan whereas aluminum which is known to have a fatigue life rarely fail. The lifespan of a new steel frame such as a Waterford Racing, has essentially an unlimited lifespan and weighs close to aluminum But this means that the workmanship is very important.

So saying a bike is responsive means almost but not quite nothing.

On 3/4/2022 8:49 AM, Dieter Britz wrote:
> I hear and read mention of a "responsive frame". What does
> this mean, and what kind of frame is responsive, and not?
>

It's a marketing term, unrelated to quantifiable values.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

Dieter Britz <dieterhansbritz@gmail.com> wrote:
> I hear and read mention of a "responsive frame". What does
> this mean, and what kind of frame is responsive, and not?
>

As others have said a fair bit of marketing fluff, this said at the
extremes bike with sharp geometry vs slack will have quicker steering.

In terms of weight and frame stiffness, only at the extremes really!

Roger Merriman

On Friday, March 4, 2022 at 2:49:27 PM UTC, Dieter Britz wrote:
> I hear and read mention of a "responsive frame". What does
> this mean, and what kind of frame is responsive, and not?
>
> --
> Dieter Britz
>
I've read the other responses and had a good chuckle.
>
Sure, marketing. But incompetent marketing, in that the subtext to me is a marketing ignoramus trying to cover up the fact that the frame is limp, and its flex will steer the bike without input from the rider, usually off the road.
>
A truly responsive bike is a tautology, because any bike with a stiff enough frame can be made quicker reacting (same thing as the now discredited "responsive") by the correct geometry, which, as Roger says, generally means steeper head angles, plus reworking the fork.
>
But I don't know why a commuter or a shopper or a social or health rider or anyone who isn't a racer would want a very quick-reacting bike. In my motor racing days, from which most people remember only that I sold a hemihead design to Chrysler, in fact I was a chassis and suspension specialist. Back then I would have said, cuttingly, "Don't give me this marketing crap about quick reactions. What you mean is that've you've bodged up an oversteering frame, dangerous in most hands." Apparently we have an example belonging to a forum member in Tom's Colnago.
>
For those who don't have the background and the experience, a neutral-steering bike could also be described as being lethally unpredictable because you'll never know whether it will put you in the ditch or under the onrushing truck until you're there already. Zero utility.
>
My own bikes are all set up to understeer. The consequential predictability and stability of line almost regardless of road surface makes the essential difference on downhill descents at speed on bad roads when I'm leaving the road racers behind with white brackets of fear beside their lips.
>
Much more at "In praise of riding low pressure tyres fast" if you haven't seen it yet:
http://thorncyclesforum.co.uk/index.php?topic=3798.msg16360#msg16360
It's worth reading the entire thread for the thoughtful additions and useful links by other cyclists.
>
Andre Jute
Ah, them were the days!
>

On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
[...]
> My own bikes are all set up to understeer. The consequential
> predictability and stability of line almost regardless of road surface
> makes the essential difference on downhill descents at speed on bad
> roads when I'm leaving the road racers behind with white brackets of
> fear beside their lips.
[...]
> Andre Jute Ah, them were the days!

How do you set a bike up for understeer? I don't know what under-
or oversteer means.

--
Dieter Britz

On 3/5/2022 7:11 AM, Dieter Britz wrote:
> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> [...]
>> My own bikes are all set up to understeer. The consequential
>> predictability and stability of line almost regardless of road surface
>> makes the essential difference on downhill descents at speed on bad
>> roads when I'm leaving the road racers behind with white brackets of
>> fear beside their lips.
> [...]
>> Andre Jute Ah, them were the days!
>
> How do you set a bike up for understeer? I don't know what under-
> or oversteer means.

Change the length of the stem.

Marshall “Major” Taylor apparently won a lot of races due to his
sliding, adjustable-length, stem. I don't think that there's any such
animal still available (though adjustable stems that simultaneously
change the height and reach are available so you could get the same
effect if the height of the stem on the steer tube is also adjustable.

One company did introduce a sliding, adjustable-length stem, but not
sure if it made it to market:
<https://bikerumor.com/just-going-to-drop-this-right-here-3fstech-slams-that-stem-with-aim-dropper-stem/>.

On 3/5/2022 9:11 AM, Dieter Britz wrote:
> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> [...]
>> My own bikes are all set up to understeer. The consequential
>> predictability and stability of line almost regardless of road surface
>> makes the essential difference on downhill descents at speed on bad
>> roads when I'm leaving the road racers behind with white brackets of
>> fear beside their lips.
> [...]
>> Andre Jute Ah, them were the days!
>
> How do you set a bike up for understeer? I don't know what under-
> or oversteer means.
>

Standard front geometry should be neutral[1] and designers
know the system well.
https://dclxvi.org/chunk/tech/trail/image/trail.jpg

In that case, when turning the wheel side to side, the frame
will neither rise nor fall.

In an understeer design like this:
http://www.yellowjersey.org/gcdl1.html

The frame rises when the handlebar is turned, which is to
say the bicycle travel in a straight path unless coerced
otherwise. This may be desired for unpaved roads and/or
heavy cargo loads. Put another way, the rider/bicycle/cargo
weight must be lifted to turn the handlebar.

The inverse, oversteer, makes a bicycle less stable (='more
responsive') and rider effort is needed to keep it in a
straight path. When the fork turns, the frame falls:
http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg

[1] Riders request variations and designers create specialty
vehicles but neutral is the standard.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On 3/5/2022 9:38 AM, sms wrote:
> On 3/5/2022 7:11 AM, Dieter Britz wrote:
>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>> [...]
>>> My own bikes are all set up to understeer. The consequential
>>> predictability and stability of line almost regardless of
>>> road surface
>>> makes the essential difference on downhill descents at
>>> speed on bad
>>> roads when I'm leaving the road racers behind with white
>>> brackets of
>>> fear beside their lips.
>> [...]
>>> Andre Jute Ah, them were the days!
>>
>> How do you set a bike up for understeer? I don't know what
>> under-
>> or oversteer means.
>
> Change the length of the stem.
>
> Marshall “Major” Taylor apparently won a lot of races
> due to his sliding, adjustable-length, stem. I don't think
> that there's any such animal still available (though
> adjustable stems that simultaneously change the height and
> reach are available so you could get the same effect if the
> height of the stem on the steer tube is also adjustable.
>
> One company did introduce a sliding, adjustable-length stem,
> but not sure if it made it to market:
> <https://bikerumor.com/just-going-to-drop-this-right-here-3fstech-slams-that-stem-with-aim-dropper-stem/>.
>
>

There are more adjustable track stems than there are
customers for adjustable track stems:

https://farm2.static.flickr.com/1091/1388506099_1fbe0f3e6c.jpg

https://4.bp.blogspot.com/-kMkQ0P8YqAI/VGTzbaPhhyI/AAAAAAAAMJw/TqGkUescR9I/s1600/IMG_9582.JPG

https://cicli-berlinetta.com/wp-content/uploads/2021/02/3TTT-Silver-4.jpg

https://velobase.com/CompImages/Stems/F8626E1F-2BED-4340-BFCE-D48BBB83D3F8.jpeg

https://lh3.googleusercontent.com/-FriYEkikkYI/TX_vylsFc6I/AAAAAAAAAE8/q6xUQCsI7b0/s1600/DSC09995.JPG

Five examples from four countries.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On 3/5/2022 8:08 AM, AMuzi wrote:

<snip>

> There are more adjustable track stems than there are customers for
> adjustable track stems:
>
> https://farm2.static.flickr.com/1091/1388506099_1fbe0f3e6c.jpg
> https://4.bp.blogspot.com/-kMkQ0P8YqAI/VGTzbaPhhyI/AAAAAAAAMJw/TqGkUescR9I/s1600/IMG_9582.JPG
> https://cicli-berlinetta.com/wp-content/uploads/2021/02/3TTTilver-4.jpg
> https://velobase.com/CompImages/Stems/F8626E1F-2BED-4340-BFCE-D48BBB83D3F8.jpeg
> https://lh3.googleusercontent.com/-FriYEkikkYI/TX_vylsFc6I/AAAAAAAAAE8/q6xUQCsI7b0/s1600/DSC09995.JPG
> Five examples from four countries.

Those are all quill stems for threaded headsets

For threadless, I could not find anything other than the one I provided
the link to.

On 3/5/2022 11:02 AM, AMuzi wrote:
> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>> [...]
>>> My own bikes are all set up to understeer. The consequential
>>> predictability and stability of line almost regardless of road surface
>>> makes the  essential difference on downhill descents at speed on bad
>>> roads when I'm leaving the road racers behind with white brackets of
>>> fear beside their lips.
>> [...]
>>> Andre Jute Ah, them were the days!
>>
>> How do you set a bike up for understeer? I don't know what under-
>> or oversteer means.
>>
>
>
> Standard front geometry should be neutral[1] and designers know the
> system well.
> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>
> In that case, when turning the wheel side to side, the frame will
> neither rise nor fall.
>
> In an understeer design like this:
> http://www.yellowjersey.org/gcdl1.html
>
> The frame rises when the handlebar is turned, which is to say the
> bicycle travel in a straight path unless coerced otherwise. This may be
> desired for unpaved roads and/or heavy cargo loads. Put another way, the
> rider/bicycle/cargo weight must be lifted to turn the handlebar.
>
> The inverse, oversteer, makes a bicycle less stable (='more responsive')
> and rider effort is needed to keep it in a straight path. When the fork
> turns, the frame falls:
> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg

Sorry, I think "the frame will neither rise nor fall" is incorrect. If
the front end geometry generates any "trail" at all, the frame must fall.

Look at http://www.yellowjersey.org/gcdl1.html again. Draw a line
representing the steering axis down to the ground. Next, draw a line
from the tire contact point directly to (and perpendicular to) the
steering axis. I suppose we could call that the 'lever arm' of the
contact point.

That 'lever arm' slants upwards from the contact point to the steering
axis. If you 'swing' it to the side by turning the handlebars, it rises
relative to the bike. IOW, if you clamped the top tube in a fixed
position and height, the 'swing' would cause the contact point to rise.
Or, switching reference frames, if you leave the tire normally on the
ground, the frame will fall.

I don't have a bike with a head angle as slack as the black one in the
photo, but I just measured my touring bike. As with every other bike
I've checked, turning the bars causes the frame to drop a bit.

See "Wheel Flop" at
https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/

"Wheel flop is similar to trail in that it is determined by the
combination of head tube angle and fork rake, however it is concerned
with how the position of the front axle changes as the handlebars are
turned. In almost all instances, the height of the front axle is lowered
when this happens"

--
- Frank Krygowski

On 3/5/2022 12:25 PM, Frank Krygowski wrote:
> On 3/5/2022 11:02 AM, AMuzi wrote:
>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>>> [...]
>>>> My own bikes are all set up to understeer. The
>>>> consequential
>>>> predictability and stability of line almost regardless
>>>> of road surface
>>>> makes the essential difference on downhill descents at
>>>> speed on bad
>>>> roads when I'm leaving the road racers behind with white
>>>> brackets of
>>>> fear beside their lips.
>>> [...]
>>>> Andre Jute Ah, them were the days!
>>>
>>> How do you set a bike up for understeer? I don't know
>>> what under-
>>> or oversteer means.
>>>
>>
>>
>> Standard front geometry should be neutral[1] and designers
>> know the system well.
>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>>
>> In that case, when turning the wheel side to side, the
>> frame will neither rise nor fall.
>>
>> In an understeer design like this:
>> http://www.yellowjersey.org/gcdl1.html
>>
>> The frame rises when the handlebar is turned, which is to
>> say the bicycle travel in a straight path unless coerced
>> otherwise. This may be desired for unpaved roads and/or
>> heavy cargo loads. Put another way, the
>> rider/bicycle/cargo weight must be lifted to turn the
>> handlebar.
>>
>> The inverse, oversteer, makes a bicycle less stable
>> (='more responsive') and rider effort is needed to keep it
>> in a straight path. When the fork turns, the frame falls:
>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>
>
> Sorry, I think "the frame will neither rise nor fall" is
> incorrect. If the front end geometry generates any "trail"
> at all, the frame must fall.
>
> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
> line representing the steering axis down to the ground.
> Next, draw a line from the tire contact point directly to
> (and perpendicular to) the steering axis. I suppose we could
> call that the 'lever arm' of the contact point.
>
> That 'lever arm' slants upwards from the contact point to
> the steering axis. If you 'swing' it to the side by turning
> the handlebars, it rises relative to the bike. IOW, if you
> clamped the top tube in a fixed position and height, the
> 'swing' would cause the contact point to rise. Or, switching
> reference frames, if you leave the tire normally on the
> ground, the frame will fall.
>
> I don't have a bike with a head angle as slack as the black
> one in the photo, but I just measured my touring bike. As
> with every other bike I've checked, turning the bars causes
> the frame to drop a bit.
>
> See "Wheel Flop" at
> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
>
>
> "Wheel flop is similar to trail in that it is determined by
> the combination of head tube angle and fork rake, however it
> is concerned with how the position of the front axle changes
> as the handlebars are turned. In almost all instances, the
> height of the front axle is lowered when this happens"
>

You have a few bicycles handy. Try turning the handlebars
while observing the front end of the frame. Your bicycles
should all be pretty close to zero height change, maybe a
millimeter or two, nothing significant.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On 3/5/2022 12:25 PM, Frank Krygowski wrote:
> On 3/5/2022 11:02 AM, AMuzi wrote:
>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>>> [...]
>>>> My own bikes are all set up to understeer. The
>>>> consequential
>>>> predictability and stability of line almost regardless
>>>> of road surface
>>>> makes the essential difference on downhill descents at
>>>> speed on bad
>>>> roads when I'm leaving the road racers behind with white
>>>> brackets of
>>>> fear beside their lips.
>>> [...]
>>>> Andre Jute Ah, them were the days!
>>>
>>> How do you set a bike up for understeer? I don't know
>>> what under-
>>> or oversteer means.
>>>
>>
>>
>> Standard front geometry should be neutral[1] and designers
>> know the system well.
>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>>
>> In that case, when turning the wheel side to side, the
>> frame will neither rise nor fall.
>>
>> In an understeer design like this:
>> http://www.yellowjersey.org/gcdl1.html
>>
>> The frame rises when the handlebar is turned, which is to
>> say the bicycle travel in a straight path unless coerced
>> otherwise. This may be desired for unpaved roads and/or
>> heavy cargo loads. Put another way, the
>> rider/bicycle/cargo weight must be lifted to turn the
>> handlebar.
>>
>> The inverse, oversteer, makes a bicycle less stable
>> (='more responsive') and rider effort is needed to keep it
>> in a straight path. When the fork turns, the frame falls:
>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>
>
> Sorry, I think "the frame will neither rise nor fall" is
> incorrect. If the front end geometry generates any "trail"
> at all, the frame must fall.
>
> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
> line representing the steering axis down to the ground.
> Next, draw a line from the tire contact point directly to
> (and perpendicular to) the steering axis. I suppose we could
> call that the 'lever arm' of the contact point.
>
> That 'lever arm' slants upwards from the contact point to
> the steering axis. If you 'swing' it to the side by turning
> the handlebars, it rises relative to the bike. IOW, if you
> clamped the top tube in a fixed position and height, the
> 'swing' would cause the contact point to rise. Or, switching
> reference frames, if you leave the tire normally on the
> ground, the frame will fall.
>
> I don't have a bike with a head angle as slack as the black
> one in the photo, but I just measured my touring bike. As
> with every other bike I've checked, turning the bars causes
> the frame to drop a bit.
>
> See "Wheel Flop" at
> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
>
>
> "Wheel flop is similar to trail in that it is determined by
> the combination of head tube angle and fork rake, however it
> is concerned with how the position of the front axle changes
> as the handlebars are turned. In almost all instances, the
> height of the front axle is lowered when this happens"
>

Experiment report:

Using a four-foot aluminum level I put one end on a table
and the other end on the front of the top tube of a medium
(56cm) Gunnar Road with Michelin 23 tires. Turning the
handlebar, I observe the bubble doesn't move.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On Saturday, March 5, 2022 at 8:08:57 AM UTC-8, AMuzi wrote:
> On 3/5/2022 9:38 AM, sms wrote:
> > On 3/5/2022 7:11 AM, Dieter Britz wrote:
> >> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> >> [...]
> >>> My own bikes are all set up to understeer. The consequential
> >>> predictability and stability of line almost regardless of
> >>> road surface
> >>> makes the essential difference on downhill descents at
> >>> speed on bad
> >>> roads when I'm leaving the road racers behind with white
> >>> brackets of
> >>> fear beside their lips.
> >> [...]
> >>> Andre Jute Ah, them were the days!
> >>
> >> How do you set a bike up for understeer? I don't know what
> >> under-
> >> or oversteer means.
> >
> > Change the length of the stem.
> >
> > Marshall “Major†Taylor apparently won a lot of races
> > due to his sliding, adjustable-length, stem. I don't think
> > that there's any such animal still available (though
> > adjustable stems that simultaneously change the height and
> > reach are available so you could get the same effect if the
> > height of the stem on the steer tube is also adjustable.
> >
> > One company did introduce a sliding, adjustable-length stem,
> > but not sure if it made it to market:
> > <https://bikerumor.com/just-going-to-drop-this-right-here-3fstech-slams-that-stem-with-aim-dropper-stem/>.
> >
> >
> There are more adjustable track stems than there are
> customers for adjustable track stems:
>
> https://farm2.static.flickr.com/1091/1388506099_1fbe0f3e6c.jpg
>
> https://4.bp.blogspot.com/-kMkQ0P8YqAI/VGTzbaPhhyI/AAAAAAAAMJw/TqGkUescR9I/s1600/IMG_9582.JPG
>
> https://cicli-berlinetta.com/wp-content/uploads/2021/02/3TTT-Silver-4.jpg
>
> https://velobase.com/CompImages/Stems/F8626E1F-2BED-4340-BFCE-D48BBB83D3F8.jpeg
>
> https://lh3.googleusercontent.com/-FriYEkikkYI/TX_vylsFc6I/AAAAAAAAAE8/q6xUQCsI7b0/s1600/DSC09995.JPG
>
> Five examples from four countries.

Those adjustable stems used to be handy for initial setup of the bike. Not much else otherwise

On Saturday, March 5, 2022 at 11:25:58 AM UTC-8, AMuzi wrote:
> On 3/5/2022 12:25 PM, Frank Krygowski wrote:
> > On 3/5/2022 11:02 AM, AMuzi wrote:
> >> On 3/5/2022 9:11 AM, Dieter Britz wrote:
> >>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> >>> [...]
> >>>> My own bikes are all set up to understeer. The
> >>>> consequential
> >>>> predictability and stability of line almost regardless
> >>>> of road surface
> >>>> makes the essential difference on downhill descents at
> >>>> speed on bad
> >>>> roads when I'm leaving the road racers behind with white
> >>>> brackets of
> >>>> fear beside their lips.
> >>> [...]
> >>>> Andre Jute Ah, them were the days!
> >>>
> >>> How do you set a bike up for understeer? I don't know
> >>> what under-
> >>> or oversteer means.
> >>>
> >>
> >>
> >> Standard front geometry should be neutral[1] and designers
> >> know the system well.
> >> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
> >>
> >> In that case, when turning the wheel side to side, the
> >> frame will neither rise nor fall.
> >>
> >> In an understeer design like this:
> >> http://www.yellowjersey.org/gcdl1.html
> >>
> >> The frame rises when the handlebar is turned, which is to
> >> say the bicycle travel in a straight path unless coerced
> >> otherwise. This may be desired for unpaved roads and/or
> >> heavy cargo loads. Put another way, the
> >> rider/bicycle/cargo weight must be lifted to turn the
> >> handlebar.
> >>
> >> The inverse, oversteer, makes a bicycle less stable
> >> (='more responsive') and rider effort is needed to keep it
> >> in a straight path. When the fork turns, the frame falls:
> >> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
> >
> >
> > Sorry, I think "the frame will neither rise nor fall" is
> > incorrect. If the front end geometry generates any "trail"
> > at all, the frame must fall.
> >
> > Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
> > line representing the steering axis down to the ground.
> > Next, draw a line from the tire contact point directly to
> > (and perpendicular to) the steering axis. I suppose we could
> > call that the 'lever arm' of the contact point.
> >
> > That 'lever arm' slants upwards from the contact point to
> > the steering axis. If you 'swing' it to the side by turning
> > the handlebars, it rises relative to the bike. IOW, if you
> > clamped the top tube in a fixed position and height, the
> > 'swing' would cause the contact point to rise. Or, switching
> > reference frames, if you leave the tire normally on the
> > ground, the frame will fall.
> >
> > I don't have a bike with a head angle as slack as the black
> > one in the photo, but I just measured my touring bike. As
> > with every other bike I've checked, turning the bars causes
> > the frame to drop a bit.
> >
> > See "Wheel Flop" at
> > https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
> >
> >
> > "Wheel flop is similar to trail in that it is determined by
> > the combination of head tube angle and fork rake, however it
> > is concerned with how the position of the front axle changes
> > as the handlebars are turned. In almost all instances, the
> > height of the front axle is lowered when this happens"
> >
> Experiment report:
>
> Using a four-foot aluminum level I put one end on a table
> and the other end on the front of the top tube of a medium
> (56cm) Gunnar Road with Michelin 23 tires. Turning the
> handlebar, I observe the bubble doesn't move.

Using a 4 foot bubble level on my Trek Alpha also shows no motion at all of the bubble.

On Sat, 05 Mar 2022 10:02:25 -0600, AMuzi <am@yellowjersey.org> wrote:

>On 3/5/2022 9:11 AM, Dieter Britz wrote:
>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>> [...]
>>> My own bikes are all set up to understeer. The consequential
>>> predictability and stability of line almost regardless of road surface
>>> makes the essential difference on downhill descents at speed on bad
>>> roads when I'm leaving the road racers behind with white brackets of
>>> fear beside their lips.
>> [...]
>>> Andre Jute Ah, them were the days!
>>
>> How do you set a bike up for understeer? I don't know what under-
>> or oversteer means.
>>
>
>
>Standard front geometry should be neutral[1] and designers
>know the system well.
>https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>
>In that case, when turning the wheel side to side, the frame
>will neither rise nor fall.
>
>In an understeer design like this:
>http://www.yellowjersey.org/gcdl1.html
>
>The frame rises when the handlebar is turned, which is to
>say the bicycle travel in a straight path unless coerced
>otherwise. This may be desired for unpaved roads and/or
>heavy cargo loads. Put another way, the rider/bicycle/cargo
>weight must be lifted to turn the handlebar.
>
>The inverse, oversteer, makes a bicycle less stable (='more
>responsive') and rider effort is needed to keep it in a
>straight path. When the fork turns, the frame falls:
>http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>
>[1] Riders request variations and designers create specialty
>vehicles but neutral is the standard.

Is this term under/over steer as used for bicycles have the same
meaning that it does for motorcycles and autos? Which usually means
that the vehicle does not follow the curved path that the front
wheel(s) does. Example of extreme oversteer:
https://www.youtube.com/watch?v=acA_mGWbLOQ
--
Cheers,

John B.

On 3/5/2022 2:25 PM, AMuzi wrote:
> On 3/5/2022 12:25 PM, Frank Krygowski wrote:
>> On 3/5/2022 11:02 AM, AMuzi wrote:
>>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>>>> [...]
>>>>> My own bikes are all set up to understeer. The
>>>>> consequential
>>>>> predictability and stability of line almost regardless
>>>>> of road surface
>>>>> makes the  essential difference on downhill descents at
>>>>> speed on bad
>>>>> roads when I'm leaving the road racers behind with white
>>>>> brackets of
>>>>> fear beside their lips.
>>>> [...]
>>>>> Andre Jute Ah, them were the days!
>>>>
>>>> How do you set a bike up for understeer? I don't know
>>>> what under-
>>>> or oversteer means.
>>>>
>>>
>>>
>>> Standard front geometry should be neutral[1] and designers
>>> know the system well.
>>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>>>
>>> In that case, when turning the wheel side to side, the
>>> frame will neither rise nor fall.
>>>
>>> In an understeer design like this:
>>> http://www.yellowjersey.org/gcdl1.html
>>>
>>> The frame rises when the handlebar is turned, which is to
>>> say the bicycle travel in a straight path unless coerced
>>> otherwise. This may be desired for unpaved roads and/or
>>> heavy cargo loads. Put another way, the
>>> rider/bicycle/cargo weight must be lifted to turn the
>>> handlebar.
>>>
>>> The inverse, oversteer, makes a bicycle less stable
>>> (='more responsive') and rider effort is needed to keep it
>>> in a straight path. When the fork turns, the frame falls:
>>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>>>
>>
>>
>> Sorry, I think "the frame will neither rise nor fall" is
>> incorrect. If the front end geometry generates any "trail"
>> at all, the frame must fall.
>>
>> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
>> line representing the steering axis down to the ground.
>> Next, draw a line from the tire contact point directly to
>> (and perpendicular to) the steering axis. I suppose we could
>> call that the 'lever arm' of the contact point.
>>
>> That 'lever arm' slants upwards from the contact point to
>> the steering axis. If you 'swing' it to the side by turning
>> the handlebars, it rises relative to the bike. IOW, if you
>> clamped the top tube in a fixed position and height, the
>> 'swing' would cause the contact point to rise. Or, switching
>> reference frames, if you leave the tire normally on the
>> ground, the frame will fall.
>>
>> I don't have a bike with a head angle as slack as the black
>> one in the photo, but I just measured my touring bike. As
>> with every other bike I've checked, turning the bars causes
>> the frame to drop a bit.
>>
>> See "Wheel Flop" at
>> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
>>
>>
>>
>> "Wheel flop is similar to trail in that it is determined by
>> the combination of head tube angle and fork rake, however it
>> is concerned with how the position of the front axle changes
>> as the handlebars are turned. In almost all instances, the
>> height of the front axle is lowered when this happens"
>>
>
> Experiment report:
>
> Using a four-foot aluminum level I put one end on a table and the other
> end on the front of the top tube of a medium (56cm) Gunnar Road with
> Michelin 23 tires. Turning the handlebar, I observe the bubble doesn't
> move.

OK, help me understand.

Again, ISTM that if we marked the tire-to road contact point with chalk,
then rotated the bars 360 degrees, that chalked point would describe a
circle. The circle would be inclined to horizontal by (90 - head tube
angle), with its high point directly forward. The marked point on the
tire would be farthest below the head tube's height with the bars
straight ahead. It would get closer to the head tube (or IOW the head
tube would drop) at any other steering angle.

Is there some other factor I'm not visualizing that would apply a
contrary action, to cancel out this effect? So far I can't think of one.

I checked my Cannondale again. I held a meter stick vertically, using my
fingers to pinch it to the top tube. I can easily feel the relative
motion. At a 45 degree steering angle (admittedly, used only for
balancing at super slow speeds) it seems the frame drops between one and
tow millimeters. At lesser steering angles the motion is almost
imperceptible, but as I visualize the geometry, it seems it must be there.

One thing I just noticed: The tire contact point actually changes as the
steering angle increases. Judging by the spokes' position, at 45 degrees
steering, the contact point has moved forward about 10 degrees. Does
this somehow affect things?

--
- Frank Krygowski

On Saturday, March 5, 2022 at 8:06:38 PM UTC, cycl...@gmail.com wrote:
> On Saturday, March 5, 2022 at 8:08:57 AM UTC-8, AMuzi wrote:
> > On 3/5/2022 9:38 AM, sms wrote:
> > > On 3/5/2022 7:11 AM, Dieter Britz wrote:
> > >> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> > >> [...]
> > >>> My own bikes are all set up to understeer. The consequential
> > >>> predictability and stability of line almost regardless of
> > >>> road surface
> > >>> makes the essential difference on downhill descents at
> > >>> speed on bad
> > >>> roads when I'm leaving the road racers behind with white
> > >>> brackets of
> > >>> fear beside their lips.
> > >> [...]
> > >>> Andre Jute Ah, them were the days!
> > >>
> > >> How do you set a bike up for understeer? I don't know what
> > >> under-
> > >> or oversteer means.
> > >
> > > Change the length of the stem.
> > >
> > > Marshall “Major†Taylor apparently won a lot of races
> > > due to his sliding, adjustable-length, stem. I don't think
> > > that there's any such animal still available (though
> > > adjustable stems that simultaneously change the height and
> > > reach are available so you could get the same effect if the
> > > height of the stem on the steer tube is also adjustable.
> > >
> > > One company did introduce a sliding, adjustable-length stem,
> > > but not sure if it made it to market:
> > > <https://bikerumor.com/just-going-to-drop-this-right-here-3fstech-slams-that-stem-with-aim-dropper-stem/>.
> > >
> > >
> > There are more adjustable track stems than there are
> > customers for adjustable track stems:
> >
> > https://farm2.static.flickr.com/1091/1388506099_1fbe0f3e6c.jpg
> >
> > https://4.bp.blogspot.com/-kMkQ0P8YqAI/VGTzbaPhhyI/AAAAAAAAMJw/TqGkUescR9I/s1600/IMG_9582.JPG
> >
> > https://cicli-berlinetta.com/wp-content/uploads/2021/02/3TTT-Silver-4.jpg
> >
> > https://velobase.com/CompImages/Stems/F8626E1F-2BED-4340-BFCE-D48BBB83D3F8.jpeg
> >
> > https://lh3.googleusercontent.com/-FriYEkikkYI/TX_vylsFc6I/AAAAAAAAAE8/q6xUQCsI7b0/s1600/DSC09995.JPG
> >
> > Five examples from four countries.
> Those adjustable stems used to be handy for initial setup of the bike. Not much else otherwise
>
Actually, there's one exception to this rule. Royal Dutch Gazelle offers an OEM proprietary stem on many of their bikes, IIRC called the Switch. Whatever it is called, it is a toollessly adjustable stem. You flip up the lever and then you can raise or lower the stem on the pivot at the steerer tube end, and rotate the handlebars within their clasp at the front end. I used this stem which came on my Gazelle Toulouse, a Dutch stadssportief- or vakansie-fiets, basically a well trimmed commuter with North Road bars, to set a ***truck-assisted*** personal ton-up record, turning the swivel down and then rotating the handlebars so that the grips pointed almost vertically to the road, to get the most aerodynamic posture possible on the bike. Took about five minutes because some of the cabling had to be adjusted. Another five minutes after I set the record to restore the bike to its respectable commuter image. Pic of the bike in question about halfway down the page here:
http://coolmainpress.com/BICYCLINGgazelletoulouse.html
About twenty years ago I tried to buy one of these the magic stems for another bike and discovered they come only for 1in quill stems.

Andre Jute
*** For the morons who take personal umbrage when I leave this off and then cause months and years of unpleasantness for everyone when I drop-kick them over the houses for their arrogance -- shame on you jerks.

On Saturday, March 5, 2022 at 3:11:06 PM UTC, Dieter Britz wrote:
> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> [...]
> > My own bikes are all set up to understeer. The consequential
> > predictability and stability of line almost regardless of road surface
> > makes the essential difference on downhill descents at speed on bad
> > roads when I'm leaving the road racers behind with white brackets of
> > fear beside their lips.
> [...]
> > Andre Jute Ah, them were the days!
> How do you set a bike up for understeer? I don't know what under-
> or oversteer means.
>
> --
> Dieter Britz

You've already had some good answers here, Dieter. Even Scharfie managed to get a technicality right: you can make the bike less reactive by simply fitting a wider handlebar so that the same distance of hand movement on the wide bar as compared to the narrower bar creates a smaller input at the contact patch. But that's mickey mouse stuff, finishing-up details for those who have to take whatever frame a manufacturer offers, and who perhaps made the wrong choice, or who are gimmicking a best available compromise right.

Ideally, starting from the drawing board, a faster-reacting bike has a steeper geometry, say a head tube angle of 72 degrees, and an understeering bike will have more laid-back angle of say 68 degrees. Andrew Muzi published photos of these two bikes. If you draw these these head angles out and then put a fork with the same offset on each, you will discover that the head angle, which is also the fork angle (so obvious that we normally don't say it), influences the trail of the front wheel. The trail is the distance between a perpendicular line running from the road surface to the wheel centre and the projection of the fork angle to the ground (if, as is true in the majority of cases, the fork shaft is straight and the fork blades continue that line until their lower-end curve starts). It should be obvious to you now that different trail distances are required for the different concepts, fast-reacting and stable (small amount of understeer).

At this point you can further influence the steering by changing forks with various amounts of offset and thus different amounts of trail which in turn give different ratios of effect to steering inputs.

Let us consider a bike and frame you bought as a set, and for one reason or another cannot change. What can you do to influence the handling? For a start, you could possibly bend the forks to change the trail, but on anything but mild steel you're just looking for trouble doing so; I imagine a responsible LBS will refuse to help you. But sometimes you can spread forks, especially in steel, a few millimeters, so you can fit fatter tyres, which by themselves will give you more stable handling by generally raising the bike so that the trail is longer. Draw it out. You'll be amazed. Narrower tyres will shorten the trail by dropping the bike a few millimeters and quicken the response. This effect, either way, is magnified by more or less rubber being in contact with the road, so that there is more or less friction to be overcome by steering inputs. Next, try changing the pressure in your tyres: the max on the sidewall is not a recommendation but an outer limit for the thoughtless. In ten years of riding 60mm Schwalbe Big Apples at pressures of 2 bar and replenished once a month when it had fallen to 1.6 or 1.5 bar, I had two snakebite punctures, one my fault for crashing through a new pothole at over 50kph, the other picked up on a building site where I was consulting the guy who operated the cordless angle grinder on how long it would take to grind through an arm of my best quality Abus D-lock. I could make even those Big Apples react faster by going to 3 bar but then they would be less stable on rough roads and bloody uncomfortable all the time, because they're the bike's main suspension: it would be a waste of expensive tyres, and the cornering power of my low inflation regime, very important on the small lanes that wander downhill through the fields, would just be gone. Notice the interplay between understeer, fat tyres, low pressure and speed and cornering power. I assume that you know the Utopia Kranich I ride has a very long wheelbase -- my bike is over two meters long, another factor in slowing the response to steering inputs in order to enhance stability.

Okay, now what is all this stability for? Or alternatively, how much of it do we want? Quite frankly, my bike, which for such a large bike is actually a lightweight (specially drawn Columbus tubes) and is made heavy only by fitting the biggest and strongest of everything, plus an electric motor and a humongous battery, and normally carrying heavy painting gear in the pannier basket, at slow speed has heavy steering. I could tune it to be lighter at walking speed but won't because the motor has a walking speed setting which rolls the bike and the steering instantly lightens up, and once you're going even a handful of clicks per hour, the steering is light, until at high speed it is very light, just heavy enough to give me some road feel. I also have 620mm wide North Road bars so that making small smooth inputs doesn't take any concentration.

I drove Porsche until I was almost middle-aged, but I drove a Porsche across Europe, from Cambridge in the English Fens to Nardo in the boot of Italy where I was testing, just once, when the air traffic controller's strike coincided with my trans-continental car, a Bentley Turbo, being in pieces while I fitted a limited slip diff. It was just too much of a pain paying constant attention to the wretched little buzzbomb's infernal tendency to head for the wall or the ditch for that far when I could set the same averages in a comfortable family saloon. I take the same attitude to bicycles.

All these small changes on an existing frame and fork I'm talking about add up cumulatively. You'll know when you've gone too far to one side or the other when your oversteering bike falls over its own front wheel and gives you a face-plant, or when your understeering bike requires too much input from you to make a fast curve -- notice that with the stable bike nothing too bad happens to you, though you might get wet in the ditch.

As for Andrew's joke about a neutral-steering bike, the example he shows would very likely be as nervous as a quarterhorse stallion, and as likely to throw you off. There's no such thing as neutral steering, either in cars or in bikes*; "neutral" is just a marketing euphemism for "bad understeer, plant you on your face at first opportunity, throw you under truck at next opportunity".

One more thing. You could possibly grade a bike for under- or over-steer by placing a scale on the contact patch under the tyre, and measuring the rise and fall caused by the handlebars converted to weight. The oversteering bike will become lighter, the understeering bike resists inputs by becoming heavier, pushing into the road for more friction. If you want to measure distance instead, you'll still need the scale for conversion to pounds/feet or whatever unit you prefer; the edge of the rim is a good place to make measurements with your wife's dress-hemming measure or the spike that comes out of a vernier caliper for depth measurements.

If you have any further questions, ask.

Andre Jute
* I wish Jobst were here to think through this sort of thing for us.

On 3/5/2022 8:45 PM, Frank Krygowski wrote:
> On 3/5/2022 2:25 PM, AMuzi wrote:
>> On 3/5/2022 12:25 PM, Frank Krygowski wrote:
>>> On 3/5/2022 11:02 AM, AMuzi wrote:
>>>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>>>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>>>>> [...]
>>>>>> My own bikes are all set up to understeer. The
>>>>>> consequential
>>>>>> predictability and stability of line almost regardless
>>>>>> of road surface
>>>>>> makes the essential difference on downhill
>>>>>> descents at
>>>>>> speed on bad
>>>>>> roads when I'm leaving the road racers behind with white
>>>>>> brackets of
>>>>>> fear beside their lips.
>>>>> [...]
>>>>>> Andre Jute Ah, them were the days!
>>>>>
>>>>> How do you set a bike up for understeer? I don't know
>>>>> what under-
>>>>> or oversteer means.
>>>>>
>>>>
>>>>
>>>> Standard front geometry should be neutral[1] and designers
>>>> know the system well.
>>>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>>>>
>>>> In that case, when turning the wheel side to side, the
>>>> frame will neither rise nor fall.
>>>>
>>>> In an understeer design like this:
>>>> http://www.yellowjersey.org/gcdl1.html
>>>>
>>>> The frame rises when the handlebar is turned, which is to
>>>> say the bicycle travel in a straight path unless coerced
>>>> otherwise. This may be desired for unpaved roads and/or
>>>> heavy cargo loads. Put another way, the
>>>> rider/bicycle/cargo weight must be lifted to turn the
>>>> handlebar.
>>>>
>>>> The inverse, oversteer, makes a bicycle less stable
>>>> (='more responsive') and rider effort is needed to keep it
>>>> in a straight path. When the fork turns, the frame falls:
>>>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>>>>
>>>
>>>
>>> Sorry, I think "the frame will neither rise nor fall" is
>>> incorrect. If the front end geometry generates any "trail"
>>> at all, the frame must fall.
>>>
>>> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
>>> line representing the steering axis down to the ground.
>>> Next, draw a line from the tire contact point directly to
>>> (and perpendicular to) the steering axis. I suppose we could
>>> call that the 'lever arm' of the contact point.
>>>
>>> That 'lever arm' slants upwards from the contact point to
>>> the steering axis. If you 'swing' it to the side by turning
>>> the handlebars, it rises relative to the bike. IOW, if you
>>> clamped the top tube in a fixed position and height, the
>>> 'swing' would cause the contact point to rise. Or, switching
>>> reference frames, if you leave the tire normally on the
>>> ground, the frame will fall.
>>>
>>> I don't have a bike with a head angle as slack as the black
>>> one in the photo, but I just measured my touring bike. As
>>> with every other bike I've checked, turning the bars causes
>>> the frame to drop a bit.
>>>
>>> See "Wheel Flop" at
>>> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
>>>
>>>
>>>
>>> "Wheel flop is similar to trail in that it is determined by
>>> the combination of head tube angle and fork rake, however it
>>> is concerned with how the position of the front axle changes
>>> as the handlebars are turned. In almost all instances, the
>>> height of the front axle is lowered when this happens"
>>>
>>
>> Experiment report:
>>
>> Using a four-foot aluminum level I put one end on a table
>> and the other end on the front of the top tube of a medium
>> (56cm) Gunnar Road with Michelin 23 tires. Turning the
>> handlebar, I observe the bubble doesn't move.
>
> OK, help me understand.
>
> Again, ISTM that if we marked the tire-to road contact point
> with chalk, then rotated the bars 360 degrees, that chalked
> point would describe a circle. The circle would be inclined
> to horizontal by (90 - head tube angle), with its high point
> directly forward. The marked point on the tire would be
> farthest below the head tube's height with the bars straight
> ahead. It would get closer to the head tube (or IOW the head
> tube would drop) at any other steering angle.
>
> Is there some other factor I'm not visualizing that would
> apply a contrary action, to cancel out this effect? So far I
> can't think of one.
>
> I checked my Cannondale again. I held a meter stick
> vertically, using my fingers to pinch it to the top tube. I
> can easily feel the relative motion. At a 45 degree steering
> angle (admittedly, used only for balancing at super slow
> speeds) it seems the frame drops between one and tow
> millimeters. At lesser steering angles the motion is almost
> imperceptible, but as I visualize the geometry, it seems it
> must be there.
>
> One thing I just noticed: The tire contact point actually
> changes as the steering angle increases. Judging by the
> spokes' position, at 45 degrees steering, the contact point
> has moved forward about 10 degrees. Does this somehow affect
> things?
>

On a 360-degree fork turn I have no idea but you're probably
right. For normal range, as you note 45 deg left or right,
any height change is between zero and negligible.

Crashed frames with damaged forks and changed head angles
exhibit wild changes, as do specialty machines designed for
over- or under- steer effect.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On 3/6/2022 5:30 AM, Andre Jute wrote:
> On Saturday, March 5, 2022 at 3:11:06 PM UTC, Dieter Britz wrote:
>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>> [...]
>>> My own bikes are all set up to understeer. The consequential
>>> predictability and stability of line almost regardless of road surface
>>> makes the essential difference on downhill descents at speed on bad
>>> roads when I'm leaving the road racers behind with white brackets of
>>> fear beside their lips.
>> [...]
>>> Andre Jute Ah, them were the days!
>> How do you set a bike up for understeer? I don't know what under-
>> or oversteer means.
>>
>> --
>> Dieter Britz
>
> You've already had some good answers here, Dieter. Even Scharfie managed to get a technicality right: you can make the bike less reactive by simply fitting a wider handlebar so that the same distance of hand movement on the wide bar as compared to the narrower bar creates a smaller input at the contact patch. But that's mickey mouse stuff, finishing-up details for those who have to take whatever frame a manufacturer offers, and who perhaps made the wrong choice, or who are gimmicking a best available compromise right.
>
> Ideally, starting from the drawing board, a faster-reacting bike has a steeper geometry, say a head tube angle of 72 degrees, and an understeering bike will have more laid-back angle of say 68 degrees. Andrew Muzi published photos of these two bikes. If you draw these these head angles out and then put a fork with the same offset on each, you will discover that the head angle, which is also the fork angle (so obvious that we normally don't say it), influences the trail of the front wheel. The trail is the distance between a perpendicular line running from the road surface to the wheel centre and the projection of the fork angle to the ground (if, as is true in the majority of cases, the fork shaft is straight and the fork blades continue that line until their lower-end curve starts). It should be obvious to you now that different trail distances are required for the different concepts, fast-reacting and stable (small amount of understeer).
>
> At this point you can further influence the steering by changing forks with various amounts of offset and thus different amounts of trail which in turn give different ratios of effect to steering inputs.
>
> Let us consider a bike and frame you bought as a set, and for one reason or another cannot change. What can you do to influence the handling? For a start, you could possibly bend the forks to change the trail, but on anything but mild steel you're just looking for trouble doing so; I imagine a responsible LBS will refuse to help you. But sometimes you can spread forks, especially in steel, a few millimeters, so you can fit fatter tyres, which by themselves will give you more stable handling by generally raising the bike so that the trail is longer. Draw it out. You'll be amazed. Narrower tyres will shorten the trail by dropping the bike a few millimeters and quicken the response. This effect, either way, is magnified by more or less rubber being in contact with the road, so that there is more or less friction to be overcome by steering inputs. Next, try changing the pressure in your tyres: the max on the sidewall is not a recommendation but an outer limit for the thoughtless. In t
en years of riding 60mm Schwalbe Big Apples at pressures of 2 bar and replenished once a month when it had fallen to 1.6 or 1.5 bar, I had two snakebite punctures, one my fault for crashing through a new pothole at over 50kph, the other picked up on a building site where I was consulting the guy who operated the cordless angle grinder on how long it would take to grind through an arm of my best quality Abus D-lock. I could make even those Big Apples react faster by going to 3 bar but then they would be less stable on rough roads and bloody uncomfortable all the time, because they're the bike's main suspension: it would be a waste of expensive tyres, and the cornering power of my low inflation regime, very important on the small lanes that wander downhill through the fields, would just be gone. Notice the interplay between understeer, fat tyres, low pressure and speed and cornering power. I assume that you know the Utopia Kranich I ride has a very long wheelbase -- my bike is over two
meters long, another factor in slowing the response to steering inputs in order to enhance stability.
>
> Okay, now what is all this stability for? Or alternatively, how much of it do we want? Quite frankly, my bike, which for such a large bike is actually a lightweight (specially drawn Columbus tubes) and is made heavy only by fitting the biggest and strongest of everything, plus an electric motor and a humongous battery, and normally carrying heavy painting gear in the pannier basket, at slow speed has heavy steering. I could tune it to be lighter at walking speed but won't because the motor has a walking speed setting which rolls the bike and the steering instantly lightens up, and once you're going even a handful of clicks per hour, the steering is light, until at high speed it is very light, just heavy enough to give me some road feel. I also have 620mm wide North Road bars so that making small smooth inputs doesn't take any concentration.
>
> I drove Porsche until I was almost middle-aged, but I drove a Porsche across Europe, from Cambridge in the English Fens to Nardo in the boot of Italy where I was testing, just once, when the air traffic controller's strike coincided with my trans-continental car, a Bentley Turbo, being in pieces while I fitted a limited slip diff. It was just too much of a pain paying constant attention to the wretched little buzzbomb's infernal tendency to head for the wall or the ditch for that far when I could set the same averages in a comfortable family saloon. I take the same attitude to bicycles.
>
> All these small changes on an existing frame and fork I'm talking about add up cumulatively. You'll know when you've gone too far to one side or the other when your oversteering bike falls over its own front wheel and gives you a face-plant, or when your understeering bike requires too much input from you to make a fast curve -- notice that with the stable bike nothing too bad happens to you, though you might get wet in the ditch.
>
> As for Andrew's joke about a neutral-steering bike, the example he shows would very likely be as nervous as a quarterhorse stallion, and as likely to throw you off. There's no such thing as neutral steering, either in cars or in bikes*; "neutral" is just a marketing euphemism for "bad understeer, plant you on your face at first opportunity, throw you under truck at next opportunity".
>
> One more thing. You could possibly grade a bike for under- or over-steer by placing a scale on the contact patch under the tyre, and measuring the rise and fall caused by the handlebars converted to weight. The oversteering bike will become lighter, the understeering bike resists inputs by becoming heavier, pushing into the road for more friction. If you want to measure distance instead, you'll still need the scale for conversion to pounds/feet or whatever unit you prefer; the edge of the rim is a good place to make measurements with your wife's dress-hemming measure or the spike that comes out of a vernier caliper for depth measurements.
>
> If you have any further questions, ask.
>
> Andre Jute
> * I wish Jobst were here to think through this sort of thing for us.
>

There's more than head angle and rake.

Fork height and tire width directly change trail. Weight
distribution is another not always considered effect.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On Sunday, March 6, 2022 at 10:58:17 a.m. UTC-5, AMuzi wrote:
> On 3/5/2022 8:45 PM, Frank Krygowski wrote:
> > On 3/5/2022 2:25 PM, AMuzi wrote:
> >> On 3/5/2022 12:25 PM, Frank Krygowski wrote:
> >>> On 3/5/2022 11:02 AM, AMuzi wrote:
> >>>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
> >>>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> >>>>> [...]
> >>>>>> My own bikes are all set up to understeer. The
> >>>>>> consequential
> >>>>>> predictability and stability of line almost regardless
> >>>>>> of road surface
> >>>>>> makes the essential difference on downhill
> >>>>>> descents at
> >>>>>> speed on bad
> >>>>>> roads when I'm leaving the road racers behind with white
> >>>>>> brackets of
> >>>>>> fear beside their lips.
> >>>>> [...]
> >>>>>> Andre Jute Ah, them were the days!
> >>>>>
> >>>>> How do you set a bike up for understeer? I don't know
> >>>>> what under-
> >>>>> or oversteer means.
> >>>>>
> >>>>
> >>>>
> >>>> Standard front geometry should be neutral[1] and designers
> >>>> know the system well.
> >>>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
> >>>>
> >>>> In that case, when turning the wheel side to side, the
> >>>> frame will neither rise nor fall.
> >>>>
> >>>> In an understeer design like this:
> >>>> http://www.yellowjersey.org/gcdl1.html
> >>>>
> >>>> The frame rises when the handlebar is turned, which is to
> >>>> say the bicycle travel in a straight path unless coerced
> >>>> otherwise. This may be desired for unpaved roads and/or
> >>>> heavy cargo loads. Put another way, the
> >>>> rider/bicycle/cargo weight must be lifted to turn the
> >>>> handlebar.
> >>>>
> >>>> The inverse, oversteer, makes a bicycle less stable
> >>>> (='more responsive') and rider effort is needed to keep it
> >>>> in a straight path. When the fork turns, the frame falls:
> >>>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
> >>>>
> >>>
> >>>
> >>> Sorry, I think "the frame will neither rise nor fall" is
> >>> incorrect. If the front end geometry generates any "trail"
> >>> at all, the frame must fall.
> >>>
> >>> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
> >>> line representing the steering axis down to the ground.
> >>> Next, draw a line from the tire contact point directly to
> >>> (and perpendicular to) the steering axis. I suppose we could
> >>> call that the 'lever arm' of the contact point.
> >>>
> >>> That 'lever arm' slants upwards from the contact point to
> >>> the steering axis. If you 'swing' it to the side by turning
> >>> the handlebars, it rises relative to the bike. IOW, if you
> >>> clamped the top tube in a fixed position and height, the
> >>> 'swing' would cause the contact point to rise. Or, switching
> >>> reference frames, if you leave the tire normally on the
> >>> ground, the frame will fall.
> >>>
> >>> I don't have a bike with a head angle as slack as the black
> >>> one in the photo, but I just measured my touring bike. As
> >>> with every other bike I've checked, turning the bars causes
> >>> the frame to drop a bit.
> >>>
> >>> See "Wheel Flop" at
> >>> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
> >>>
> >>>
> >>>
> >>> "Wheel flop is similar to trail in that it is determined by
> >>> the combination of head tube angle and fork rake, however it
> >>> is concerned with how the position of the front axle changes
> >>> as the handlebars are turned. In almost all instances, the
> >>> height of the front axle is lowered when this happens"
> >>>
> >>
> >> Experiment report:
> >>
> >> Using a four-foot aluminum level I put one end on a table
> >> and the other end on the front of the top tube of a medium
> >> (56cm) Gunnar Road with Michelin 23 tires. Turning the
> >> handlebar, I observe the bubble doesn't move.
> >
> > OK, help me understand.
> >
> > Again, ISTM that if we marked the tire-to road contact point
> > with chalk, then rotated the bars 360 degrees, that chalked
> > point would describe a circle. The circle would be inclined
> > to horizontal by (90 - head tube angle), with its high point
> > directly forward. The marked point on the tire would be
> > farthest below the head tube's height with the bars straight
> > ahead. It would get closer to the head tube (or IOW the head
> > tube would drop) at any other steering angle.
> >
> > Is there some other factor I'm not visualizing that would
> > apply a contrary action, to cancel out this effect? So far I
> > can't think of one.
> >
> > I checked my Cannondale again. I held a meter stick
> > vertically, using my fingers to pinch it to the top tube. I
> > can easily feel the relative motion. At a 45 degree steering
> > angle (admittedly, used only for balancing at super slow
> > speeds) it seems the frame drops between one and tow
> > millimeters. At lesser steering angles the motion is almost
> > imperceptible, but as I visualize the geometry, it seems it
> > must be there.
> >
> > One thing I just noticed: The tire contact point actually
> > changes as the steering angle increases. Judging by the
> > spokes' position, at 45 degrees steering, the contact point
> > has moved forward about 10 degrees. Does this somehow affect
> > things?
> >
> On a 360-degree fork turn I have no idea but you're probably
> right. For normal range, as you note 45 deg left or right,
> any height change is between zero and negligible.
>
> Crashed frames with damaged forks and changed head angles
> exhibit wild changes, as do specialty machines designed for
> over- or under- steer effect.
> --
> Andrew Muzi
> <www.yellowjersey.org/>
> Open every day since 1 April, 1971

I have a red Bianchi that was given to me as a frameset because the owner ran into a parked car and bent the downtube and the headtube a bit. Just for fun I built the frameset up with some spare components I had lying around. I took it out to a parking lot to try riding it and I was amazed at how well it tracked and how easy it was to ride no hands. I liked the ride so much t hat I'm restoring it back to its original Suntour Cyclone components.

Cheers

On 3/6/2022 11:10 AM, Sir Ridesalot wrote:
> On Sunday, March 6, 2022 at 10:58:17 a.m. UTC-5, AMuzi wrote:
>> On 3/5/2022 8:45 PM, Frank Krygowski wrote:
>>> On 3/5/2022 2:25 PM, AMuzi wrote:
>>>> On 3/5/2022 12:25 PM, Frank Krygowski wrote:
>>>>> On 3/5/2022 11:02 AM, AMuzi wrote:
>>>>>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>>>>>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>>>>>>> [...]
>>>>>>>> My own bikes are all set up to understeer. The
>>>>>>>> consequential
>>>>>>>> predictability and stability of line almost regardless
>>>>>>>> of road surface
>>>>>>>> makes the essential difference on downhill
>>>>>>>> descents at
>>>>>>>> speed on bad
>>>>>>>> roads when I'm leaving the road racers behind with white
>>>>>>>> brackets of
>>>>>>>> fear beside their lips.
>>>>>>> [...]
>>>>>>>> Andre Jute Ah, them were the days!
>>>>>>>
>>>>>>> How do you set a bike up for understeer? I don't know
>>>>>>> what under-
>>>>>>> or oversteer means.
>>>>>>>
>>>>>>
>>>>>>
>>>>>> Standard front geometry should be neutral[1] and designers
>>>>>> know the system well.
>>>>>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>>>>>>
>>>>>> In that case, when turning the wheel side to side, the
>>>>>> frame will neither rise nor fall.
>>>>>>
>>>>>> In an understeer design like this:
>>>>>> http://www.yellowjersey.org/gcdl1.html
>>>>>>
>>>>>> The frame rises when the handlebar is turned, which is to
>>>>>> say the bicycle travel in a straight path unless coerced
>>>>>> otherwise. This may be desired for unpaved roads and/or
>>>>>> heavy cargo loads. Put another way, the
>>>>>> rider/bicycle/cargo weight must be lifted to turn the
>>>>>> handlebar.
>>>>>>
>>>>>> The inverse, oversteer, makes a bicycle less stable
>>>>>> (='more responsive') and rider effort is needed to keep it
>>>>>> in a straight path. When the fork turns, the frame falls:
>>>>>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>>>>>>
>>>>>
>>>>>
>>>>> Sorry, I think "the frame will neither rise nor fall" is
>>>>> incorrect. If the front end geometry generates any "trail"
>>>>> at all, the frame must fall.
>>>>>
>>>>> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
>>>>> line representing the steering axis down to the ground.
>>>>> Next, draw a line from the tire contact point directly to
>>>>> (and perpendicular to) the steering axis. I suppose we could
>>>>> call that the 'lever arm' of the contact point.
>>>>>
>>>>> That 'lever arm' slants upwards from the contact point to
>>>>> the steering axis. If you 'swing' it to the side by turning
>>>>> the handlebars, it rises relative to the bike. IOW, if you
>>>>> clamped the top tube in a fixed position and height, the
>>>>> 'swing' would cause the contact point to rise. Or, switching
>>>>> reference frames, if you leave the tire normally on the
>>>>> ground, the frame will fall.
>>>>>
>>>>> I don't have a bike with a head angle as slack as the black
>>>>> one in the photo, but I just measured my touring bike. As
>>>>> with every other bike I've checked, turning the bars causes
>>>>> the frame to drop a bit.
>>>>>
>>>>> See "Wheel Flop" at
>>>>> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
>>>>>
>>>>>
>>>>>
>>>>> "Wheel flop is similar to trail in that it is determined by
>>>>> the combination of head tube angle and fork rake, however it
>>>>> is concerned with how the position of the front axle changes
>>>>> as the handlebars are turned. In almost all instances, the
>>>>> height of the front axle is lowered when this happens"
>>>>>
>>>>
>>>> Experiment report:
>>>>
>>>> Using a four-foot aluminum level I put one end on a table
>>>> and the other end on the front of the top tube of a medium
>>>> (56cm) Gunnar Road with Michelin 23 tires. Turning the
>>>> handlebar, I observe the bubble doesn't move.
>>>
>>> OK, help me understand.
>>>
>>> Again, ISTM that if we marked the tire-to road contact point
>>> with chalk, then rotated the bars 360 degrees, that chalked
>>> point would describe a circle. The circle would be inclined
>>> to horizontal by (90 - head tube angle), with its high point
>>> directly forward. The marked point on the tire would be
>>> farthest below the head tube's height with the bars straight
>>> ahead. It would get closer to the head tube (or IOW the head
>>> tube would drop) at any other steering angle.
>>>
>>> Is there some other factor I'm not visualizing that would
>>> apply a contrary action, to cancel out this effect? So far I
>>> can't think of one.
>>>
>>> I checked my Cannondale again. I held a meter stick
>>> vertically, using my fingers to pinch it to the top tube. I
>>> can easily feel the relative motion. At a 45 degree steering
>>> angle (admittedly, used only for balancing at super slow
>>> speeds) it seems the frame drops between one and tow
>>> millimeters. At lesser steering angles the motion is almost
>>> imperceptible, but as I visualize the geometry, it seems it
>>> must be there.
>>>
>>> One thing I just noticed: The tire contact point actually
>>> changes as the steering angle increases. Judging by the
>>> spokes' position, at 45 degrees steering, the contact point
>>> has moved forward about 10 degrees. Does this somehow affect
>>> things?
>>>
>> On a 360-degree fork turn I have no idea but you're probably
>> right. For normal range, as you note 45 deg left or right,
>> any height change is between zero and negligible.
>>
>> Crashed frames with damaged forks and changed head angles
>> exhibit wild changes, as do specialty machines designed for
>> over- or under- steer effect.

> I have a red Bianchi that was given to me as a frameset because the owner ran into a parked car and bent the downtube and the headtube a bit. Just for fun I built the frameset up with some spare components I had lying around. I took it out to a parking lot to try riding it and I was amazed at how well it tracked and how easy it was to ride no hands. I liked the ride so much t hat I'm restoring it back to its original Suntour Cyclone components.
>
> Cheers
>

A 'field enhancement' of Bianchi's design!
A few minutes with a protractor, tape measure and a similar
road bicycle might show you why.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On Sunday, March 6, 2022 at 4:08:41 PM UTC, AMuzi wrote:
> On 3/6/2022 5:30 AM, Andre Jute wrote:
> > On Saturday, March 5, 2022 at 3:11:06 PM UTC, Dieter Britz wrote:
> >> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
> >> [...]
> >>> My own bikes are all set up to understeer. The consequential
> >>> predictability and stability of line almost regardless of road surface
> >>> makes the essential difference on downhill descents at speed on bad
> >>> roads when I'm leaving the road racers behind with white brackets of
> >>> fear beside their lips.
> >> [...]
> >>> Andre Jute Ah, them were the days!
> >> How do you set a bike up for understeer? I don't know what under-
> >> or oversteer means.
> >>
> >> --
> >> Dieter Britz
> >
> > You've already had some good answers here, Dieter. Even Scharfie managed to get a technicality right: you can make the bike less reactive by simply fitting a wider handlebar so that the same distance of hand movement on the wide bar as compared to the narrower bar creates a smaller input at the contact patch. But that's mickey mouse stuff, finishing-up details for those who have to take whatever frame a manufacturer offers, and who perhaps made the wrong choice, or who are gimmicking a best available compromise right.
> >
> > Ideally, starting from the drawing board, a faster-reacting bike has a steeper geometry, say a head tube angle of 72 degrees, and an understeering bike will have more laid-back angle of say 68 degrees. Andrew Muzi published photos of these two bikes. If you draw these these head angles out and then put a fork with the same offset on each, you will discover that the head angle, which is also the fork angle (so obvious that we normally don't say it), influences the trail of the front wheel. The trail is the distance between a perpendicular line running from the road surface to the wheel centre and the projection of the fork angle to the ground (if, as is true in the majority of cases, the fork shaft is straight and the fork blades continue that line until their lower-end curve starts). It should be obvious to you now that different trail distances are required for the different concepts, fast-reacting and stable (small amount of understeer).
> >
> > At this point you can further influence the steering by changing forks with various amounts of offset and thus different amounts of trail which in turn give different ratios of effect to steering inputs.
> >
> > Let us consider a bike and frame you bought as a set, and for one reason or another cannot change. What can you do to influence the handling? For a start, you could possibly bend the forks to change the trail, but on anything but mild steel you're just looking for trouble doing so; I imagine a responsible LBS will refuse to help you. But sometimes you can spread forks, especially in steel, a few millimeters, so you can fit fatter tyres, which by themselves will give you more stable handling by generally raising the bike so that the trail is longer. Draw it out. You'll be amazed. Narrower tyres will shorten the trail by dropping the bike a few millimeters and quicken the response. This effect, either way, is magnified by more or less rubber being in contact with the road, so that there is more or less friction to be overcome by steering inputs. Next, try changing the pressure in your tyres: the max on the sidewall is not a recommendation but an outer limit for the thoughtless. In t
> en years of riding 60mm Schwalbe Big Apples at pressures of 2 bar and replenished once a month when it had fallen to 1.6 or 1.5 bar, I had two snakebite punctures, one my fault for crashing through a new pothole at over 50kph, the other picked up on a building site where I was consulting the guy who operated the cordless angle grinder on how long it would take to grind through an arm of my best quality Abus D-lock. I could make even those Big Apples react faster by going to 3 bar but then they would be less stable on rough roads and bloody uncomfortable all the time, because they're the bike's main suspension: it would be a waste of expensive tyres, and the cornering power of my low inflation regime, very important on the small lanes that wander downhill through the fields, would just be gone. Notice the interplay between understeer, fat tyres, low pressure and speed and cornering power. I assume that you know the Utopia Kranich I ride has a very long wheelbase -- my bike is over two
> meters long, another factor in slowing the response to steering inputs in order to enhance stability.
> >
> > Okay, now what is all this stability for? Or alternatively, how much of it do we want? Quite frankly, my bike, which for such a large bike is actually a lightweight (specially drawn Columbus tubes) and is made heavy only by fitting the biggest and strongest of everything, plus an electric motor and a humongous battery, and normally carrying heavy painting gear in the pannier basket, at slow speed has heavy steering. I could tune it to be lighter at walking speed but won't because the motor has a walking speed setting which rolls the bike and the steering instantly lightens up, and once you're going even a handful of clicks per hour, the steering is light, until at high speed it is very light, just heavy enough to give me some road feel. I also have 620mm wide North Road bars so that making small smooth inputs doesn't take any concentration.
> >
> > I drove Porsche until I was almost middle-aged, but I drove a Porsche across Europe, from Cambridge in the English Fens to Nardo in the boot of Italy where I was testing, just once, when the air traffic controller's strike coincided with my trans-continental car, a Bentley Turbo, being in pieces while I fitted a limited slip diff. It was just too much of a pain paying constant attention to the wretched little buzzbomb's infernal tendency to head for the wall or the ditch for that far when I could set the same averages in a comfortable family saloon. I take the same attitude to bicycles.
> >
> > All these small changes on an existing frame and fork I'm talking about add up cumulatively. You'll know when you've gone too far to one side or the other when your oversteering bike falls over its own front wheel and gives you a face-plant, or when your understeering bike requires too much input from you to make a fast curve -- notice that with the stable bike nothing too bad happens to you, though you might get wet in the ditch.
> >
> > As for Andrew's joke about a neutral-steering bike, the example he shows would very likely be as nervous as a quarterhorse stallion, and as likely to throw you off. There's no such thing as neutral steering, either in cars or in bikes*; "neutral" is just a marketing euphemism for "bad understeer, plant you on your face at first opportunity, throw you under truck at next opportunity".
> >
> > One more thing. You could possibly grade a bike for under- or over-steer by placing a scale on the contact patch under the tyre, and measuring the rise and fall caused by the handlebars converted to weight. The oversteering bike will become lighter, the understeering bike resists inputs by becoming heavier, pushing into the road for more friction. If you want to measure distance instead, you'll still need the scale for conversion to pounds/feet or whatever unit you prefer; the edge of the rim is a good place to make measurements with your wife's dress-hemming measure or the spike that comes out of a vernier caliper for depth measurements.
> >
> > If you have any further questions, ask.
> >
> > Andre Jute
> > * I wish Jobst were here to think through this sort of thing for us.
> >
> There's more than head angle and rake.
>
> Fork height and tire width directly change trail. Weight
> distribution is another not always considered effect.
> --
> Andrew Muzi
> <www.yellowjersey.org/>
> Open every day since 1 April, 1971
>
Quite so. That's why I laid emphasis on tyre changes, because they're one of the easiest ways for the cyclist to change the handling of his bike. As for weight distribution, on the antisocial media one can't go on at the exhaustive length possible in a lecture hall or a tutorial room with a few favored students*, and one naturally assumes that an adult cyclist has the common sense not to distribute weight on the bike dangerously.

Actually the most important thing I didn't say outright, though it is implied in "cumulative", is that a bicycle suspension and steering is a matter of additive subtleties, not all of which are well understood. For instance, a known unknown, not solved in roundabout three-quarters of a century, is why a reversed fork doesn't interfere terminally with the bike's steering.

Andre Jute
* But not necessarily in books which can only be a commercial length. When my DESIGNING AND BUILDING SPECIAL CARS was published Arthur Mallock, the late Major, the most influential British designer and manufacturer of racing cars for club racers, called me to say, "Your publisher should have allowed you at least half that many pages again. You'll just have to write another book, old boy." The Major is another we could have done with in this thread, as he knew everything there is to know about suspension jacking and corner weights.
>

On 3/6/2022 10:58 AM, AMuzi wrote:
> On 3/5/2022 8:45 PM, Frank Krygowski wrote:
>> On 3/5/2022 2:25 PM, AMuzi wrote:
>>> On 3/5/2022 12:25 PM, Frank Krygowski wrote:
>>>> On 3/5/2022 11:02 AM, AMuzi wrote:
>>>>> On 3/5/2022 9:11 AM, Dieter Britz wrote:
>>>>>> On Sat, 05 Mar 2022 02:50:18 -0800, Andre Jute wrote:
>>>>>> [...]
>>>>>>> My own bikes are all set up to understeer. The
>>>>>>> consequential
>>>>>>> predictability and stability of line almost regardless
>>>>>>> of road surface
>>>>>>> makes the  essential difference on downhill
>>>>>>> descents at
>>>>>>> speed on bad
>>>>>>> roads when I'm leaving the road racers behind with white
>>>>>>> brackets of
>>>>>>> fear beside their lips.
>>>>>> [...]
>>>>>>> Andre Jute Ah, them were the days!
>>>>>>
>>>>>> How do you set a bike up for understeer? I don't know
>>>>>> what under-
>>>>>> or oversteer means.
>>>>>>
>>>>>
>>>>>
>>>>> Standard front geometry should be neutral[1] and designers
>>>>> know the system well.
>>>>> https://dclxvi.org/chunk/tech/trail/image/trail.jpg
>>>>>
>>>>> In that case, when turning the wheel side to side, the
>>>>> frame will neither rise nor fall.
>>>>>
>>>>> In an understeer design like this:
>>>>> http://www.yellowjersey.org/gcdl1.html
>>>>>
>>>>> The frame rises when the handlebar is turned, which is to
>>>>> say the bicycle travel in a straight path unless coerced
>>>>> otherwise. This may be desired for unpaved roads and/or
>>>>> heavy cargo loads. Put another way, the
>>>>> rider/bicycle/cargo weight must be lifted to turn the
>>>>> handlebar.
>>>>>
>>>>> The inverse, oversteer, makes a bicycle less stable
>>>>> (='more responsive') and rider effort is needed to keep it
>>>>> in a straight path. When the fork turns, the frame falls:
>>>>> http://1.bp.blogspot.com/-WJp92Vd-dMI/TtlTUAlSArI/AAAAAAAADLE/WmujhKVkXGg/s1600/sanrensho2.jpg
>>>>>
>>>>>
>>>>
>>>>
>>>> Sorry, I think "the frame will neither rise nor fall" is
>>>> incorrect. If the front end geometry generates any "trail"
>>>> at all, the frame must fall.
>>>>
>>>> Look at http://www.yellowjersey.org/gcdl1.html again. Draw a
>>>> line representing the steering axis down to the ground.
>>>> Next, draw a line from the tire contact point directly to
>>>> (and perpendicular to) the steering axis. I suppose we could
>>>> call that the 'lever arm' of the contact point.
>>>>
>>>> That 'lever arm' slants upwards from the contact point to
>>>> the steering axis. If you 'swing' it to the side by turning
>>>> the handlebars, it rises relative to the bike. IOW, if you
>>>> clamped the top tube in a fixed position and height, the
>>>> 'swing' would cause the contact point to rise. Or, switching
>>>> reference frames, if you leave the tire normally on the
>>>> ground, the frame will fall.
>>>>
>>>> I don't have a bike with a head angle as slack as the black
>>>> one in the photo, but I just measured my touring bike. As
>>>> with every other bike I've checked, turning the bars causes
>>>> the frame to drop a bit.
>>>>
>>>> See "Wheel Flop" at
>>>> https://cyclingtips.com/2018/11/the-geometry-of-bike-handling-its-all-about-the-steering/
>>>>
>>>>
>>>>
>>>>
>>>> "Wheel flop is similar to trail in that it is determined by
>>>> the combination of head tube angle and fork rake, however it
>>>> is concerned with how the position of the front axle changes
>>>> as the handlebars are turned. In almost all instances, the
>>>> height of the front axle is lowered when this happens"
>>>>
>>>
>>> Experiment report:
>>>
>>> Using a four-foot aluminum level I put one end on a table
>>> and the other end on the front of the top tube of a medium
>>> (56cm) Gunnar Road with Michelin 23 tires. Turning the
>>> handlebar, I observe the bubble doesn't move.
>>
>> OK, help me understand.
>>
>> Again, ISTM that if we marked the tire-to road contact point
>> with chalk, then rotated the bars 360 degrees, that chalked
>> point would describe a circle.  The circle would be inclined
>> to horizontal by (90 - head tube angle), with its high point
>> directly forward. The marked point on the tire would be
>> farthest below the head tube's height with the bars straight
>> ahead. It would get closer to the head tube (or IOW the head
>> tube would drop) at any other steering angle.
>>
>> Is there some other factor I'm not visualizing that would
>> apply a contrary action, to cancel out this effect? So far I
>> can't think of one.
>>
>> I checked my Cannondale again. I held a meter stick
>> vertically, using my fingers to pinch it to the top tube. I
>> can easily feel the relative motion. At a 45 degree steering
>> angle (admittedly, used only for balancing at super slow
>> speeds) it seems the frame drops between one and tow
>> millimeters. At lesser steering angles the motion is almost
>> imperceptible, but as I visualize the geometry, it seems it
>> must be there.
>>
>> One thing I just noticed: The tire contact point actually
>> changes as the steering angle increases. Judging by the
>> spokes' position, at 45 degrees steering, the contact point
>> has moved forward about 10 degrees. Does this somehow affect
>> things?
>>
>
> On a 360-degree fork turn I have no idea but you're probably right. For
> normal range, as you note 45 deg left or right, any height change is
> between zero and negligible.

I just did more geometry work. For now, I'm treating the front wheel as
a pure circle, i.e. a disc of zero thickness, or a tire of zero width.
(I'm not sure what difference tire width will make, if any.)

You're certainly right that the height change is small, at least for
small steering angles. The obvious limit is zero height change for zero
steering angle. But ISTM that as steering angle increases from zero,
there must be _some_ drop in frame height. Here's some of the geometry.

The contact point of the tire on the road occurs at the back of the
"trail," and the trail value is often easy to look up for a given bike.
Alternately it's easy to calculate from head angle H and fork offset.

Let's call the trail value T.

Spinning the fork all the way around makes the contact point trace a
circle. Its radius is R=T*cos(90-H) and that circle tilts upward 90-H
degrees. That upward tilt is the basis of what I've been saying.

Steering angle S causes the contact point to swing a bit upward along
that circle. I'll give details if desired, but using two projected views
and some fairly simple trig, the change in height as that contact point
swings up (i.e. closer to the top tube) is the amount the frame drops.
Call it D.

I get D = R * (1-cos (S)) * sin(90-H)
or
D = T * cos(90-H) * (1-cos (S)) * sin(90-H)

As I see it, for any conventional bike this is going to cause the frame
height to drop just a bit. It's not much, because the circle tilts up
only about 17 or 18 degrees, and for most riding S is small. But it must
be there.

Plugging in an extreme steering angle of 45 degrees with a 73 degree
head angle and 60 mm trail, this gives a drop of 4.91mm. Plugging in the
same values but with a more typical 10 degree steering angle gives a
drop of 0.25mm which is small indeed, but not zero. (The controlling
term is (1 - cos(S)), which is very small for normal steering angles.)

BTW, I just held the meter stick against the top tube of my ancient
Raleigh commuter/grocery bike. It too exhibited a drop as I turned the
handlebars. It's almost undetectable for small steering angles, but it's
there. It doesn't seem to be as large as 5mm, but then I don't know the
bike's head angle or trail. (Yet.)