I've thought about doing something similar but lean towards a different approach. I would use some sort of a quadrature encoder on the wheel axle to generate a series of pulses. This can go into a cheap little uC to then drive an electronic pot, iif a resistive output is desired output or used directly in a microcontroller.
The big advantage here is that you don't use mechanical parts that can wear out. I think you would need to get a pretty good pot to have a reasonable life span. Also, wear on a pot will likely change its linearity.
Phil