On car tires, shoes and other such items, having less of the material in contact with the surface underneath increases traction. Why is that? Isn’t friction a function of the contacting area and speed?
In: 11
Well….you’re talking more about the loose concept of “grip” than you are about just friction.
Friction is the coefficient of friction times force. That’s it. Contact are doesn’t matter in the slightest.
When you’re talking about real-world things designed to handle a variety of circumstances, friction isn’t the most helpful thing, because it varies a lot and isn’t the only force involved.
Off-road with appropriate tires, you’re digging into the dirt and actually pushing against it, not just dealing with the friction of it as a magical high-school class indestructible surface. So those tires act like cleats or hiking boots and dig in, and more/larger cleats can dig in to more dirt, thus applying more force before they start flinging dirt instead of moving whatever they’re supposed to move.
On-road, but with wet pavement the biggest threat to traction is that you’re not actually contacting the pavement at all, but rather the water on top of it. So instead of a smooth tire that may trap a thin layer of water between tire and pavement, you use a tire that is textured with channels to shed that water away and get down to the pavement where there’s much more friction. Same idea with shoe treads, rain boots have chunky treads with channels available for water to escape so you can make sure you’re getting to the ground rather than slipping around on the water on top of it.
On road and try, a smooth tread works just fine. In extreme circumstances, when you’re looking at stuff like racing slicks, the smooth tire may actually be heating up from the use. It both softens and conforms to the road, allowing it to push laterally against the micro-terrain of the road surface, but also in those race conditions actually becoming adhesive in which case, more surface area of adhesive means more grip.
Friction is…shaky. It can be different 2″ apart on a road depending on if there’s a drip of oil there or not. Grip is a composite of many aspects, not just friction, and a lot of them are served by digging into the surface or shedding any intervening things like water. Hence treads.
Latest Answers