Drivers issue, how do I get the wheels to spin correctly

Hello! I am a long time user of blender, short time user of the animation system (in particular drivers and constraints), in the attached blend I am trying to figure out how to get this tractor to move along a path (easy enough), with the wheels rotating based on the tractor body’s local y movement.

But the wheel movement makes no sense, for one it’s backwards, normally I would just add a generator with -x, which does work at first, but when it goes around the second half of the circle it goes in the opposite direction, how do I fix this?

Here is the file Driver Test2.blend (610 KB)

I don’t think you can use the Y movement for this because the tractor is going from right to left initially and then it will go from left to right as it go around the circle. It would be better to use a Follow Path constraint on the car body and animate the Path offset instead of using the Evaluation time modifier on the curve to move the car around the circle. You can then control the rotation of the wheel by driving it with the Path offset of the curve. To get the wheel to rotate properly you need to calculate the circumference of the wheel (about 10.7 units). The wheel therefore needs to rotate 360 degrees (6.3 radians, the driver uses radians) when the car moves 10.7 units. The movement of the car by 10.7 units is equivalent to a Path offset of about 0.08 and so the driver needs to multiply the offset by about 76.8 (6.3/0.08) to get the proper rotation.
Driver Test3.blend (612 KB)