Gravity car wheel radius selection

AI Thread Summary
Choosing the optimal wheel radius for a gravity-powered car involves balancing speed, stability, and acceleration. Smaller wheels may offer quicker acceleration but can compromise stability, while larger wheels tend to provide higher top speeds and reduced axle friction due to slower rotation at the same forward speed. The race distance plays a crucial role in this decision, influencing the trade-offs between acceleration and maximum speed. Narrow and hard wheels are recommended to minimize rolling resistance. A formula or calculation method is sought to compare the performance of 20" versus 26" wheels based on a specific course distance.
paulnist
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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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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.
 
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.
 

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