It is a known fact that car tires' quality/tread depth directly affect the braking distance. I am a little confused about the exact reasons. I can understand how tires with worse quality can lose traction completely and start skidding, but if the contact is maintained, where is the difference coming from? Can tires skid a little and then recover traction (then this intermittent skidding would make the difference in the braking distance)?
Thank you.
"It is a known fact that car tires' quality/tread depth directly affect the braking distance" Well, sort of. The 'quality' of the tire affects the dry braking distance, the tread depth/design and the 'quality' (to a much lesser extent) of the tire affect wet braking. Dry braking is pretty much a function of the compound, tire width, and inflation pressure. Tread doesn't come into it significantly (there are ifs and buts). Wet braking is largely a case of pumping water away from the contact patch, hence the importance of pressure and tread.
One of the factors in a good quality tire is that its shear module is low.
if we notice the graph of shear resistance versus applied force:
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We realize a lower shear modulus allows the tread of the tire to slide more adding to the threshold of motion before the tire skids.
Assuming the momentum $P_{normal}= mv-mo$ used to get to the threshold of motion for a normal tire
$$P_{quality-tire}>P_{normal-tire}, \therefore mv_2>mv_1 $$ $$v_2>v_1$$
So the car will not skid until higher speeds.
And even in case of a rare emergency stop, after skidding the tire because of the build-in design to generate a lot of surface heat the tire will burn a thin film on the surface turning it to a sticky surface with a higher index of friction.
