When tyres skid on a dry road, is it because friction is too low or because the rubber is not strong enough?

All other things being equal, a car with wider tyres is less likely to skid on a dry road than one with narrower tyres. As answers on related topics have made clear, the simple formula $$F=\mu N$$ does not apply to car tyres. We observe that when a car skids on a dry road, some rubber is left on the road.

Is the failure of traction in a skid caused by slipping of rubber against the road surface, or by the failure of the rubber to hold together under the high shear stress?