How to Calculate Wheel Rotation ( Blend Included)

I am facing a problem that i am not able to calculate Wheel Rotation Speed and surface.
This is 100 Frame Animation and Toy Cycle is going from Point A to Point B on a path.
The speed is chaning and Can Change depending on the Path IPO. How will I create a Wheel Rotation IPO. The Blend file is here
Both wheels are different in size.

Maybe this could help:

I have downloaded and studying.
Thanks for the link.

Hi !
On my website, in BLENDER section of the menu, you will find my Pdf tutorial for automated cars animation. A blend file is provided.
It doesnt uses a realpath, but an other method using Curve modifier.
You have only to calibrate the ration between rotation and translation,and the animation is correct at any speed, even if you edit the curve. Obviously, you’ll have to calibrate for the two wheels diameter.
Try it and let me know if you have some troubles !

Thanks Roubal.