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From experience, it appears motorcycles with a large wheelbase coupled with a long handlebar (say a modified Harley Ape Hangar) shows a noticeable tendency to veer to a side during acceleration vs a motorcycle with a short wheelbase and short handlebars. (eg. Triumph Speed Triple); is this an example of torque steering (as explained here)?

Or is there more to it? From a design standpoint, what would be the ideal ratio between wheelbase and handlebar length?

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  • $\begingroup$ The link you gave mentions a torque due to differences in the left and right drive wheels which your motorcycle doesn't have. I suspect that what you have noticed is a difference in counter-steering of the two bikes when you apply more pressure to the throttle. Longer handlebars would definitely affect the sensitivity of the counter-steer effect. I expect a longer wheelbase would, too. Is the veer to the right or the left? $\endgroup$ – Bill N Jan 14 '15 at 19:10
  • $\begingroup$ I have to believe the height of the handlebars above the frame has nothing to do with stability; the length of the fork, the angle, and the wheel base do. Could it be a matter of stiffness of the frame? $\endgroup$ – Floris Nov 24 '15 at 15:20
  • $\begingroup$ One thing that definitely causes this only occurs in bikes with a longitudinal crankshaft, such as a Moto Guzzi. When the engine speeds up, it applies a torque to the bike, tending to lean it over in a direction opposite to the direction the crankshaft spins. But Harleys have transverse crankshafts. $\endgroup$ – Ben51 Jan 25 '18 at 19:58
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a harley does not torque steer because its crankshaft is a right angles to the direction of travel. this means the torque reaction transmitted to the frame when the engine is loaded would tend to lift the front wheel, not roll the frame to the side.

An air-cooled BMW, a moto guzzi v-twin, and the honda CX series v-twins all exhibit torque steer because their crankshafts point in the direction of travel. when you goose the throttle on any of these bikes, the torque reaction from the engine will roll the bike sideways. under way, the rider has to compensate for this torque roll with steering corrections.

Even in bikes with transversely-mounted engines, though, adding power will accelerate the bike, and adding power in a turn means the rider must also add bank angle to offset the added speed so as to maintain a constant turn radius. If the rider fails to do so, adding power in a turn will necessarily increase the turn radius and thereby may run the bike "wide"- that is, off the road to the outside of the turn. The way the rider experiences this is that adding power in a turn tends to make the bike go straight- which is why bikers often roll on the throttle and accelerate when coming out of a turn.

In this sense one might claim that there is a torque-steer effect in motorcycles, in which upping the torque applied to the rear wheel causes the bike to straighten out and stop turning.

However, this is completely different from the normal usage of the term "torque steer" in front-wheel-drive cars, in which hitting the gas in a turn pulls the front wheels straight and increases the amount of steering effort required to hold the car in the turn.

In a motorcycle, wheelbase, fork angle, bar length and fork trail have no influence on this effect.

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Although your question is simple, the answer involves some rather complex modeling of dynamic systems to analyze and explain the stability of the bicycle (as well as motorcycles) and what parameters affect it. Here is an on-line article that doesn't go too deeply into the mathematics, but gives you an idea of the things one needs to consider:

http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf

I'm a control systems scientist, but have not studied or worked with non-holonomic systems of which, I believe, the bicycle system fits into. Non-holonomic means that you cannot integrate some or all of the states, and in the case of the bicycle I believe that arises from multiple dimensions of space that have to be considered in the model.

If you are seriously interested in studying the problem, there are many papers in the IEEE Xplore Digital Libarary that have addressed such analyses mostly contributed by members of the Control Systems Society. I recall one issue of Control Systems Magazine that dealt with this subject and even analyzed more exotic configurations including back-wheel steering. Supposedly back wheel steering is very unstable and can be dangerous at high speed.

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Following the link you gave in your question, torque steering as described there really happens in situations where the drive torque is applied to two wheels (front or rear), and for some reason the torque is not applied equally to both wheels.

An apparent pull to the side when you accelerate your bike hard may be related to the tension in the chain, and the way in which that would bend the frame slightly. Such bending can have all kinds of effects - especially when combined with the large flywheel effects of the engine and the wheels.

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There isn't. The handlebar length doesn't affect it either.

Maybe the Harleys are not just built that well and the sensation of the bike pulling might depend on the length of the handlebars, but the actual force has nothing to do with the handlebars length and as such there isn't an ideal length.

shorter handlebars will move less, but exhibit more torque, the long handlebars will move a longer distance at the tip but at less torque(if you have long handlebars you would have more leverage to counter any steering the bike wants to do on it's own, but that is all.

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protected by Chris Aug 29 at 9:20

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