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.
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