# Gravity car wheel radius selection

As someone who regretfully has never studied physics, I am at a loss as to how to begin to evaluate the choice of wheel radius for a gravity powered car I am building for a local gravity race. How would one go about picking a wheel radius that would maximize the speed of the vehicle?

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Hootenanny
Staff Emeritus
Gold Member
I imagine smaller wheels would be faster and yet less stable.

Top speed will probably be highest with larger wheels, while acceleration would be higher with smaller wheels. A lot depends on the distance of the race I would guess.

Danger
Gold Member
I suspect that there would be less axle friction with the bigger wheels because they won't be rotating as fast as small ones at the same forward speed. Mostly, keep them narrow and hard for less rolling resistance.

update

Is there anyone that could provide a formula to help decide whether to use 20" vs 26" wheels? I have a set figure for the course distance.