Along time ago, an engineer once told me that a rolling tire has a point on it that actually moves rearward before it moves up and forward. I'm not sure if the tire had weight on it or not. I checked with a major tire manufacturer once and they said no.

Well,
supposing that the tire is moving in a clockwise direction, which is how a car tyre moves,

it is the way a point in the tyre is supposed to move.
Imagine a spot on the tyre exactly vertically below. Aahhh, the spot on the tyre touching the road_ got it? As you start the car, the car moving in a forward direction, the spot WILL first move back; then up and then towards the front. Just as you stated.

Hope I'm able to help,
Pin~Jinx

Trueview:

Wow you made me have to think on this one (Ouch, poor brain)

First take a look at this page to see what that tire is doing.

Now you can see that the points on the tire will be moving forward (Relative to the ground)or
stopped (again relative to the ground)
where the tire is in contact with the road.

Now imagine a small hole in the road, if a small portion of the tire
pushes down below the surface you will have a situation like the "Prolate Cycloid"
on the above web page. Any point on the tire that is below the roadway
will in fact move backwards relative to the surface of the road.

Wwheeugh, did I explain that right ??

Regards Mike (AKA Byter)

Great answer Byter. But can we say that the road is represented by a line between the two ends of the prolate cycloid because it has the weight of the car on it? If so, the way that I am reading it, a point on the tire does move rearward for a short time. A ridged tire with no weight on it would not do so.

tv

Trueview:
As you mention, where the tire is in contact with the road it
flattens out into the "FOOTPRINT" tire makers like to talk about.

Since the bottem of the tire is slightly flattened a point
on the circumferance isn't going to describe a perfect cycloid.

Now maybe (I'm kind of guessing here) at the front of the tire
as it's deforming from round to flat, may move rearward
with respect to the road. If it does that, it may also do the same thing
at the rear of the tire where the rubber again moves back to a
circular configuration.

Maybe you could find something soft & round and roll it
around in front of you to see if you can see any rearward movement.

I've tried useing Mrs. Byter for this but couldn't get
her to agree to being rolled on the ground for this interesting experment.

Byter:

Thanks. I tried rolling my parakeet on the floor but the feathers hid the effect.

tv

Byter

The only way a point on the flattened portion of the tire, which is in contact with the ground, would move backward is if it slipped backward, as when one spins their tire. This, of course, would no longer be a "rolling" tire, but a slipping tire--a far different animal.

Right you are Minn. as soon as the tire is in contact with
the ground it's not going to move backwards or forward unless it's sliding.

Where I was refering to is that small portion that's in
transition from circular (where the tire's in the air}
and the flat portion in contact with the ground.

I just went to look at the tire on my truck but couldn't tell much
(These eyes arn't what they used to be )

Intuitively this would seem to be a very small radiused curve where the rubber
already in contact w/ the ground is pulling the on the part
that's just about to touch the ground.

Now I'm confuseing myself.