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There are quite a few questions about this in the general case (i.e. what is the source of the centripetal force when cornering?) but I don't understand what the origin of this force is specifically for the rear tires (assuming front wheel drive).

For the front tires, this is my understanding of the apparent perpendicular force when turning (in this instance, left) -

enter image description here

Here, the gray point is a point on the patch of tire making contact with the road, and the front tire is rotated to an angle. So, that point on the contact patch has rotational velocity (blue) that is no longer aligned with the forward velocity of the car (yellow), creating a nonzero velocity orthogonal to the tire to the right (purple), which is counteracted by static friction at the ground (green) up to whatever the grip of the tire is.

Is this understanding correct? If so, given that the back tire is not rotated/still aligned with the direction of the car, where does its centripetal come from in this scenario?

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  • $\begingroup$ Google for "oversteer skid," which is what happens when the static friction between the rear wheels and the road is broken. $\endgroup$ Sep 29, 2022 at 20:15
  • $\begingroup$ If you park the car, put it in neutral, and try to push it sideways, you will find that the static friction of both the front tires and the back tires will prevent the car from moving. When you go around a corner, the rear tires follow the front tires, but that static friction will mean that the rear tires provide the centripetal force to make the rear end of the car follow the same path as the front end of the car (if you are not going around the curve too fast). $\endgroup$ Sep 29, 2022 at 22:39
  • $\begingroup$ @DavidWhite "The rear tires follow the front tires" $\endgroup$
    – roozbubu
    Sep 30, 2022 at 18:01
  • $\begingroup$ In my current understanding, static friction at the contact patch of the rear tires (being connected to the body of the car) would counteract this force from the front tears, not go along with it. In the diagram above, if the force from the front tires was then acting on the rear tires, wouldn't static friction oppose it in the other direction? $\endgroup$
    – roozbubu
    Sep 30, 2022 at 18:07

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The reason a lateral force appears at the rear cornering wheel is because the wheel changes travel direction. How that happens is unintuitive and quickly described below.

In your singletrack example: the front and rear wheel are in static frictional contact with the road (1). The vehicle is then rolled forward.

Through a short distance of rolling, the front and rear wheel maintain static contact with the road at each contact patch. Thus, the orientation of each wheel tread within the contact patch does not change. What does change orientation with ANY amount of forward rolling is the vehicle frame (2). This describes a vertical axis torque being created through both contact patches. At some point the increasing torque changes the orientation at a wheel contact patch which means the wheel is then traveling a different direction and a lateral cornering force is created (3). enter image description here

The unintuitive part is that a cornering car changes direction and travels along a circular/curved path because all four wheels individually constantly turn. This cornering mechanism can also be found in other cornering vehicles such as a boat or snowmobile. The video below demonstrates this cornering mechanism.

https://youtu.be/-UIir0wNIEI

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  • $\begingroup$ Beautifully put, thank you $\endgroup$
    – roozbubu
    Aug 24, 2023 at 20:03

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