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Effect of speed on tire lateral force

Effect of speed on tire lateral force

Effect of speed on tire lateral force

(OP)
I am struggling to find studies on tire force variation with rolling speed. Most times only the slip angle is considered (along with combined slip, camber thrust).

It would only make sense to me that the lateral force would grow with speed due to hysteresis/damping. As the tire roll faster, with the same slip angle, the amount of time a section of tread spends in the contact patch is lower, however it experiences the same amount of shearing every time, which means it's shearing faster and faster. The faster is shears, the more resistance should be, due to viscoelastic forces. The tire tread effectively becomes stiffer.

Does my description above make sense? Is there any data to back up or debunk these observations?

Thanks!

RE: Effect of speed on tire lateral force

It's not a big deal, that is over the range 50-120 kph I don't see much. If it was significant then I'd have thought Mr Pacejka's formula would include a forward velocity term, it does not. MF is not the world's greatest tire model, but it is usable. There are of course second order effects, but which way they go is not known to me. SAE paper 760029 discusses this, as does Garcia-Pozuelo, D., Diaz, V. & Boada, M.J.L. New tyre-road contact model for applications at low speed. Int.J Automot. Technol. 15, 553–564 (2014). https://doi.org/10.1007/s12239-014-0058-y

Cheers

Greg Locock


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RE: Effect of speed on tire lateral force

There is a lot of data to back it up going back more than 50 years. Many test facilities run tests at 7.5 kph to get linear to mid range properties. Tires are spatial frequency objects, so relaxation properties have a bit of speed sensitivity as far as what influence they have on a vehicle. Usually the first test procedure run on a new tire construction is a speed sweep to identify/validate what minimum speed will suffice to get the properties wanted in order to minimize 'damage/wear' that high speed testing can produce.

RE: Effect of speed on tire lateral force

(OP)
So I get it that the hysteresis effect exists but it isn't significant enough to be accounted for. Perhaps only at Bugatti speeds it becomes of concern. If there is data on this it doesn't seem to be obvious to find. I certainly haven't tried searching very hard.

RE: Effect of speed on tire lateral force

The relaxation 'hysteresis effect' attenuates with speed. Remember its a spatial/velocity element. And relaxation is 3rd order, no better data than to see Mz tire properties develop. Not 1st, as authors with feelings but no data constantly harp on. Their use of a 1st order distance constant (and the 2/3 rev 'rule' of thumb) is necessary to converge the iteration for slip angle when both nonlinear Fy & Mx, and Mz players are involved in vehicle transient maneuvers.

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