# Nascar, Left Turns, & Torque

1. Apr 3, 2013

### Vodkacannon

Nascar races tend to use left turns. Why is this?

Well my reasoning behind this would be that when an object (like a wheel) rotates counter-clockwise, it generates torque in a direction perpendicular to its rotational plane. This torque points to the left, therefore left turns are easier than right turns when driving forward.

Now I ask you, Physics Forums, why does r×F produce a leftward torque when the object is rotating counter-clockwise? Why not rightward or some other direction? Does it have something to do with particle spin?

2. Apr 3, 2013

### bs15benny

I think it is because the wheel rotates counter-clockwise which is to the left.. and if its rotates clock-wise it rotates to the right. The direction of the wheel rotates proportional to the direction of force applied.

3. Apr 4, 2013

### rcgldr

It was just a matter of preference. Some of the road courses used by Nascar turn "right", such as Road America, Sonoma (formerly Infineon, formerly Sears Point), and Watkins Glen. Most road courses, even ones in the USA, turn "right" but there are exceptions, such as Laguna Seca and the new Circuit of the Americas (in Austin, Texas). Suzuka in Japan has a crossover point (like a figure 8), so it's a "balanced" track.

Last edited: Apr 4, 2013
4. Apr 4, 2013

### willem2

If the car is going forward in a straight line, no torque is produced by the wheels. Why do you think there is a torque?

5. Apr 4, 2013

### bs15benny

There is always a torque because the wheel is rotates but the difference between going straight and left or right is only depends on the steering

6. Apr 4, 2013

### jbriggs444

What makes you think that the wheels on a car are rotating counter-clockwise? If I look at them from the right they're rotating clockwise. If I look at them from the left they're rotating counter-clockwise.

The wheels do have non-zero angular momentum about their centers of gravity. If we adopt a right-hand rule convention, that angular momentum is leftward pointing. But that's purely a convention. We could equally well have adopted a "left-hand rule" convention. The physics would be the same. Let's ignore the convention and reason from first principles instead.

Adopt a point of view looking forward from the back of the car.

If the car steers left, the angular momentum of the wheels changes. They are now rotating somewhat counter-clockwise. A counter-clockwise torque must have been applied to the car to keep it steady. In the absence of such a torque, the bulk of the car would have tended to rotate clockwise -- out of the turn.

If the car steers right, the angular momentum of the wheels changes. They are now rotating somewhat clockwise. A clockwise torque must have been applied to the car to keep it steady. In the absence of such a torque, the bulk of the car would have tended to rotate counter-clockwise -- out of the turn.

Just as one would naively expect, there is a symmetry here. Don't let the "right-hand rule" convention convince you otherwise.

[Ignoring the direction of rotation of the engine. That could break the symmetry]

7. Apr 4, 2013

### A.T.

And when you look from car's interior, the left and the right wheels are rotating in opposite ways!

8. Apr 4, 2013

### bs15benny

I do agree with jbriggs444 and A.T :)

9. Apr 4, 2013

### NegativeDept

I've seen several explanations. This ESPN page claims it's because US horse races turn left as a reaction against UK races turning right. (I have no idea if that's true.)

I don't know enough racing history to be sure, but I suspect The Straight Dope has the right* answer. US drivers drive on the right, so passenger cars have the driver on the left side of the car. NASCAR originally used modified passenger cars. Turning left means the driver gets a better view of the apex and more protection when hitting the wall, unless the car is going backwards.

* No pun intended.

A rotating wheel does not produce torque. A spinning object tends to continue spinning unless torque is applied to it.

I think one of the other posters mentioned this, but it's good to keep in mind because the cross product and 3D rotations can be confusing: clockwise and counterclockwise depend on what direction you're looking. A vinyl record spins clockwise as viewed from above the turntable. If you look from below, it spins counterclockwise.