Saturday, 19 May 2018

friction - Why does a tire produce more traction when sliding slightly?


It is well known in racing that driving the car on the ideal "slip angle" of the tire where it is crabbing slightly from the pointed direction produces more cornering speed than a lower slip angle or a higher one.


(More explanation as requested) I'm considering two main effects on the tire when in a turn:





  1. The tread of the tire is twisted from the angle of the wheel it is mounted to. There is more force as speed increases, and generally, more twisting.




  2. The tire slides somewhat at an angle on the road surface rather than rolling.




At low speeds, the angle between the pointed direction of the wheel (90 degrees to the axis of rotation) and the direction of travel is nearly 0. When the speed increases to the point the angle reaches about 10 degrees, the tire generate more grip and the car goes faster around the turn. (Higher angles produce lower grip)


So the grip is higher at 10 degrees of slip than at 0 or 20 degrees.



What is the physical effect that causes this increase in grip?




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