Motorcycle braking and weight transfer

[Malienation]

[QUOTE=Schuyler]
Incorrect. Actually, the physics of tire-to-pavement contact is not Coulomb friction (which is what you’ve described), where the maximum load is proportional to normal force, but is dependent on deformation of the tire into pavement irregularities and localized shear forces. This is why high-grip tires have larger cross-sections and/or contact patches, not (primarily) to preclude large-scale shear-induced failure of the rubber, but to allow for more rubber-to-road contact area. Note though, as you’ve alluded, making a tire’s contact area larger allows a softer compound for the same wear characteristics, and this softer compound will conform to the surface better giving higher grip. This is actually the “phenomenon found on pavement”. Hope this helps.
[/QUOTE]
Hmmm, I dunno. “Deformation of the tire into pavement irregularities” sounds like it would increase with narrow tires, since the higher pressure on the smaller contact patch would force better contact with irregular surfaces, no? And how are the “localized shear forces” that you’ve mentioned different than the shear forces I’ve mentioned?

[Schuyler]

[QUOTE=Malienation]
Hmmm, I dunno. “Deformation of the tire into pavement irregularities” sounds like it would increase with narrow tires, since the higher pressure on the smaller contact patch would force better contact with irregular surfaces, no? And how are the “localized shear forces” that you’ve mentioned different than the shear forces I’ve mentioned?
[/QUOTE]

My apologies if I’ve misunderstood your post, but “shredding” sounding like a large-scale effect. The discussion could get very involved, so I’m going to duck it for now. But here is a bit more information - if one does a google search on “tire friction theory” one will see that there is more going on than a simple physics model of friction.

University of South Carolina site:

Classical friction theory must be modified for tires because of their structural flexibility and the stretch of the tread rubber. Instead of depending solely on the coefficient of friction at the tire-road interface (which is determined by the nature of the road surface and the tread rubber compound), maximum stopping ability also depends on the resistance of the tread to tearing under the forces that occur during braking.

When a car is braked to a hard stop on a dry road, the maximum frictional force developed can be greater than the strength of the tread. The result is that instead of the tire merely sliding along the road, rubber is torn off the tread at the tire-road interface. Undoubtedly the tread resistance to this tearing is a combination of the rubber strength and the grooves and slots that make up the tread design.

The weight of the car is unevenly distributed over the tire-road contact area, creating areas of high and low pressure. (This is much like what you feel when you step on a pebble while walking in thin-soled shoes.) The resistance of the tread to tearing increases in the areas of higher pressure, where the tread is more compressed, causing an effective increase in traction.

Further, the size of the contact area is very important in car tires because the traction is dynamic rather than static; that is, it changes as the tire rolls along. The maximum coefficient of friction can occur anywhere in the contact area, so that the greater the area, the greater the likelihood of maximum traction. Thus, under identical load and on the same dry surface, the wider tire has a greater contact area and develops higher traction, resulting in greater stopping ability.