A car tyre requires at least 1.6mm of tread depth to be road legal but a truck, for some reason only requires 1mm? Surely a truck which requires more grip also requires more or at least the same level of tread depth as a car?
I was thinking perhaps because the truck is pressing down on the ground more and thus the friction would be better than than of a car but that doesn’t seem like a sufficient answer to be honest.
You are mistakenly equating tread depth with grip, in fact that opposite is true; the more rubber you have in contact with the road the better the grip. This is why racing cars and motorbikes utilise slick tyres.
What tread depth does bring however is better water displacement properties when driving in wet conditions. I imagine that the thinking about the different depth requirements is possibly because cars are lighter than lorries and tend to have far less wheels/tyres then it is more important for them to possess better water clearing properties than lorries require.
Ah I guess that makes sense. Thanks.