https://www.renehersecycles.com/trail-does-not-make-a-bike-stable/

An interesting area of study but no great secrets are
revealed here.

The part which caught my eye was his comment on 'wheel
flop'. The great gurus who taught me geometry strongly
emphasized that a correctly designed machine should neither
rise nor fall when the wheel is turned, i.e., tendency to
turn from rider weight or resistance to turning are both
errors. Mr Heine seems to hint that drop while turning the
fork is desirable but I've found that disrupts no-hands
riding (a good test of overall handling IMHO).
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

On 12/26/2021 12:53 PM, AMuzi wrote:
> https://www.renehersecycles.com/trail-does-not-make-a-bike-stable/
>
>
> An interesting area of study but no great secrets are revealed here.
>
> The part which caught my eye was his comment on 'wheel flop'. The great
> gurus who taught me geometry strongly emphasized that a correctly
> designed machine should neither rise nor fall when the wheel is turned,
> i.e., tendency to turn from rider weight or resistance to turning are
> both errors.

Hmm. I think any standard bike with non-zero trail must have some wheel
flop, no?

> Mr Heine seems to hint that drop while turning the fork is
> desirable but I've found that disrupts no-hands riding (a good test of
> overall handling IMHO).

I read that today, too.

The 1970s book _DeLong's Guide to Bicycles and Bicycling_ has a graph of
Fred DeLong's impressions of bike stability at various speeds for
various amounts of trail. He built a fork with what looks like rear
slotted dropouts in place of standard fork ends so he could adjust trail
for experiments.

Anyway, his curves for stability "Snaking," "Hands off," "High Speed,"
and "Gravel Road" all peak for different values of trail, with "Gravel
Road" peaking with the most trail. All those are based on his personal
judgments. (But that's what Jan Heine uses a lot as well.)

That book also contains a formula used by "cycle engineers" to give
"satisfactory steering":

Fork offset = r * tan[ (90 - Q)/2] where r = wheel radius and Q is head
angle in degrees. ISTR playing with that formula back in the 1970s just
out of curiosity.

There's also a graph of a poorly defined "stability index" generated by
an unspecified computer program.

To me, DeLong's discussion was unclear, or at least hard for me to
understand. I'd be happy to type in a couple paragraphs if people were
interested in discussing.

--
- Frank Krygowski

On Sunday, December 26, 2021 at 9:53:47 AM UTC-8, AMuzi wrote:
> https://www.renehersecycles.com/trail-does-not-make-a-bike-stable/
>
>
> An interesting area of study but no great secrets are
> revealed here.
>
> The part which caught my eye was his comment on 'wheel
> flop'. The great gurus who taught me geometry strongly
> emphasized that a correctly designed machine should neither
> rise nor fall when the wheel is turned, i.e., tendency to
> turn from rider weight or resistance to turning are both
> errors. Mr Heine seems to hint that drop while turning the
> fork is desirable but I've found that disrupts no-hands
> riding (a good test of overall handling IMHO).

I think that they were speaking rather obvious extremes. I think that the Airborne I have probably has a lot of trail since the one time I needed to make a 90 degree turn without planning it I couldn't turn the bars fast enough. On the other hand, the Douglas Ti which I just got back from a 51 mile ride in what turned out to be too much rain has no problem making those sorts of turns.

On Sunday, December 26, 2021 at 4:34:58 PM UTC-5, Frank Krygowski wrote:
> On 12/26/2021 12:53 PM, AMuzi wrote:
> > https://www.renehersecycles.com/trail-does-not-make-a-bike-stable/
> >
> >
> > An interesting area of study but no great secrets are revealed here.
> >
> > The part which caught my eye was his comment on 'wheel flop'. The great
> > gurus who taught me geometry strongly emphasized that a correctly
> > designed machine should neither rise nor fall when the wheel is turned,
> > i.e., tendency to turn from rider weight or resistance to turning are
> > both errors.
> Hmm. I think any standard bike with non-zero trail must have some wheel
> flop, no?
> > Mr Heine seems to hint that drop while turning the fork is
> > desirable but I've found that disrupts no-hands riding (a good test of
> > overall handling IMHO).
> I read that today, too.
>
> The 1970s book _DeLong's Guide to Bicycles and Bicycling_ has a graph of
> Fred DeLong's impressions of bike stability at various speeds for
> various amounts of trail. He built a fork with what looks like rear
> slotted dropouts in place of standard fork ends so he could adjust trail
> for experiments.
>
> Anyway, his curves for stability "Snaking," "Hands off," "High Speed,"
> and "Gravel Road" all peak for different values of trail, with "Gravel
> Road" peaking with the most trail. All those are based on his personal
> judgments. (But that's what Jan Heine uses a lot as well.)
>
> That book also contains a formula used by "cycle engineers" to give
> "satisfactory steering":
>
> Fork offset = r * tan[ (90 - Q)/2] where r = wheel radius and Q is head
> angle in degrees. ISTR playing with that formula back in the 1970s just
> out of curiosity.
>
> There's also a graph of a poorly defined "stability index" generated by
> an unspecified computer program.

Qu'est-ce que c'est "poorly defined"?

>
> To me, DeLong's discussion was unclear, or at least hard for me to
> understand. I'd be happy to type in a couple paragraphs if people were
> interested in discussing.
>
> --
> - Frank Krygowski

On 12/29/2021 11:00 AM, funkma...@hotmail.com wrote:
> On Sunday, December 26, 2021 at 4:34:58 PM UTC-5, Frank Krygowski wrote:
>> On 12/26/2021 12:53 PM, AMuzi wrote:
>>> https://www.renehersecycles.com/trail-does-not-make-a-bike-stable/
>>>
>>>
>>> An interesting area of study but no great secrets are revealed here.
>>>
>>> The part which caught my eye was his comment on 'wheel flop'. The great
>>> gurus who taught me geometry strongly emphasized that a correctly
>>> designed machine should neither rise nor fall when the wheel is turned,
>>> i.e., tendency to turn from rider weight or resistance to turning are
>>> both errors.
>> Hmm. I think any standard bike with non-zero trail must have some wheel
>> flop, no?
>>> Mr Heine seems to hint that drop while turning the fork is
>>> desirable but I've found that disrupts no-hands riding (a good test of
>>> overall handling IMHO).
>> I read that today, too.
>>
>> The 1970s book _DeLong's Guide to Bicycles and Bicycling_ has a graph of
>> Fred DeLong's impressions of bike stability at various speeds for
>> various amounts of trail. He built a fork with what looks like rear
>> slotted dropouts in place of standard fork ends so he could adjust trail
>> for experiments.
>>
>> Anyway, his curves for stability "Snaking," "Hands off," "High Speed,"
>> and "Gravel Road" all peak for different values of trail, with "Gravel
>> Road" peaking with the most trail. All those are based on his personal
>> judgments. (But that's what Jan Heine uses a lot as well.)
>>
>> That book also contains a formula used by "cycle engineers" to give
>> "satisfactory steering":
>>
>> Fork offset = r * tan[ (90 - Q)/2] where r = wheel radius and Q is head
>> angle in degrees. ISTR playing with that formula back in the 1970s just
>> out of curiosity.
>>
>> There's also a graph of a poorly defined "stability index" generated by
>> an unspecified computer program.
>
> Qu'est-ce que c'est "poorly defined"?
>
>>
>> To me, DeLong's discussion was unclear, or at least hard for me to
>> understand. I'd be happy to type in a couple paragraphs if people were
>> interested in discussing.
>>
>> --
>> - Frank Krygowski

What would be an example of a qualitative (numerically
comparable) value for 'stability' ?

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

On 12/29/2021 12:09 PM, AMuzi wrote:
> On 12/29/2021 11:00 AM, funkma...@hotmail.com wrote:
>> On Sunday, December 26, 2021 at 4:34:58 PM UTC-5, Frank Krygowski wrote:
>>>
>>> The 1970s book _DeLong's Guide to Bicycles and Bicycling_ has a graph of
>>> Fred DeLong's impressions of bike stability at various speeds for
>>> various amounts of trail. He built a fork with what looks like rear
>>> slotted dropouts in place of standard fork ends so he could adjust trail
>>> for experiments.
>>>
>>> Anyway, his curves for stability "Snaking," "Hands off," "High Speed,"
>>> and "Gravel Road" all peak for different values of trail, with "Gravel
>>> Road" peaking with the most trail. All those are based on his personal
>>> judgments. (But that's what Jan Heine uses a lot as well.)
>>>
>>> That book also contains a formula used by "cycle engineers" to give
>>> "satisfactory steering":
>>>
>>> Fork offset = r * tan[ (90 - Q)/2] where r = wheel radius and Q is head
>>> angle in degrees. ISTR playing with that formula back in the 1970s just
>>> out of curiosity.
>>>
>>> There's also a graph of a poorly defined "stability index" generated by
>>> an unspecified computer program.
>>
>> Qu'est-ce que c'est "poorly defined"?

Perhaps I should have said "undefined." Or at least, not defined in
DeLong's book.

There's a paragraph describing how leaning a stationary bike causes the
front wheel to turn in the direction of the lean, but turn less in that
direction as the lean is increased.

Then: "Dr. David Jones ... discovered this effect and wrote a computer
program to calculate this stabilizing tendency. The stabilizing effect
was related to wheel diameter, steering head angle and trail. Relative
values of this effect show the strength of the stabilizing force. A zero
value has no effect, a positive value is unstable, and negative values
have an increasing tendency to maintain direction."

To me, that counts as no definition at all.

>>> To me, DeLong's discussion was unclear, or at least hard for me to
>>> understand. I'd be happy to type in a couple paragraphs if people were
>>> interested in discussing.
>>>
>>> --
>>> - Frank Krygowski
>
> What would be an example of a qualitative (numerically comparable) value
> for 'stability' ?

Dr. Jones must have had some example in mind. The graph contained in
DeLong's book confidently shows numerical values for a "STABILITY INDEX"
- whatever that is! I assume it's a dimensionless quantity, since no
units are given in the graph; but above, he implies it's a force. Beyond
that, I haven't a clue.

Here's a link to that graph. See what you can make of it.

https://www.flickr.com/photos/16972296@N08/51787701196/in/dateposted-public/

--
- Frank Krygowski

On Thursday, December 30, 2021 at 9:15:49 AM UTC-8, Frank Krygowski wrote:
> On 12/29/2021 12:09 PM, AMuzi wrote:
> > On 12/29/2021 11:00 AM, funkma...@hotmail.com wrote:
> >> On Sunday, December 26, 2021 at 4:34:58 PM UTC-5, Frank Krygowski wrote:
> >>>
> >>> The 1970s book _DeLong's Guide to Bicycles and Bicycling_ has a graph of
> >>> Fred DeLong's impressions of bike stability at various speeds for
> >>> various amounts of trail. He built a fork with what looks like rear
> >>> slotted dropouts in place of standard fork ends so he could adjust trail
> >>> for experiments.
> >>>
> >>> Anyway, his curves for stability "Snaking," "Hands off," "High Speed,"
> >>> and "Gravel Road" all peak for different values of trail, with "Gravel
> >>> Road" peaking with the most trail. All those are based on his personal
> >>> judgments. (But that's what Jan Heine uses a lot as well.)
> >>>
> >>> That book also contains a formula used by "cycle engineers" to give
> >>> "satisfactory steering":
> >>>
> >>> Fork offset = r * tan[ (90 - Q)/2] where r = wheel radius and Q is head
> >>> angle in degrees. ISTR playing with that formula back in the 1970s just
> >>> out of curiosity.
> >>>
> >>> There's also a graph of a poorly defined "stability index" generated by
> >>> an unspecified computer program.
> >>
> >> Qu'est-ce que c'est "poorly defined"?
> Perhaps I should have said "undefined." Or at least, not defined in
> DeLong's book.
>
> There's a paragraph describing how leaning a stationary bike causes the
> front wheel to turn in the direction of the lean, but turn less in that
> direction as the lean is increased.
>
> Then: "Dr. David Jones ... discovered this effect and wrote a computer
> program to calculate this stabilizing tendency. The stabilizing effect
> was related to wheel diameter, steering head angle and trail. Relative
> values of this effect show the strength of the stabilizing force. A zero
> value has no effect, a positive value is unstable, and negative values
> have an increasing tendency to maintain direction."
>
> To me, that counts as no definition at all.
> >>> To me, DeLong's discussion was unclear, or at least hard for me to
> >>> understand. I'd be happy to type in a couple paragraphs if people were
> >>> interested in discussing.
> >>>
> >>> --
> >>> - Frank Krygowski
> >
> > What would be an example of a qualitative (numerically comparable) value
> > for 'stability' ?
> Dr. Jones must have had some example in mind. The graph contained in
> DeLong's book confidently shows numerical values for a "STABILITY INDEX"
> - whatever that is! I assume it's a dimensionless quantity, since no
> units are given in the graph; but above, he implies it's a force. Beyond
> that, I haven't a clue.
>
> Here's a link to that graph. See what you can make of it.
>
> https://www.flickr.com/photos/16972296@N08/51787701196/in/dateposted-public/
Looks to me like he is saying that the most stable head angle/trail is 68 degrees or so. The faster you are traveling the more you lean in the corners and the less you want the fork to move.