Re: Does a tire stop when it makes contact with the road?

The short answer is "yes, a portion of the tire does stay in contact with 
the road for a significant length of time or else there would be little 
or no traction."

If you have ever seen a commercial or other demonstration of how the 
tread design of a tire allows it to "grip the road", especially in 
standing water, they will usually show a view from beneath (through a 
sheet of glass) where each portion of the tread is shown to stay in one 
place before being lifted up.

That is one of the reasons, besides comfort, that we use rubber tires 
rather than, say, wooden wheels, as they used before the invention of 
self-propelled vehicles.

If one is being pulled, or pushed, by an outside force, traction is not 
important, except possibly for steering, so wooden or metallic wheels are 
OK for carts and wagons.

However, if you need to propel yourself by an internal engine, your drive 
wheels must have enough friction to convert the rotational motion to 
translational movement, and that requires greater contact with the ground.

There is a great temptation to say that this shows that friction is 
proportional to contact area, and sensible as that may seem, that is 
WRONG.  Friction is only proportional to weight, and a factor (or 
coefficient) determined by the interaction between the two surfaces in 
question, such as rubber and concrete.

What we see here is a mix of static (non-moving) friction and kinetic 
(moving) friction in action.  Static friction is almost always greater 
than kinetic friction, which is why it is easier to slide a heavy box 
once it is in motion than when you first try to get it moving.  
Similarly, if each point on the outside of a wheel were in continual 
motion, the amount of friction (or traction) whould diminish 
significantly once the vehicle began moving.

However, since each portion of the tire comes to a complete rest on the 
pavement before being lifted off again, each portion contributes to 
greater traction due to static friction.

BTW, I hope you have learned as much about this subject as I recently 
have.  As I "refreshed my memory" on this subject, I now think that I 
must have missed a couple of physics classes when they covered this 
subject.