Gravity car wheel radius selection

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Discussion Overview

The discussion revolves around selecting the appropriate wheel radius for a gravity-powered car intended for a local gravity race. Participants explore how wheel size might influence speed, stability, and other performance factors, considering both theoretical and practical aspects of the design.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • One participant expresses uncertainty about how to evaluate wheel radius for maximizing speed in a gravity car.
  • Another participant suggests that smaller wheels might lead to higher speeds but could compromise stability.
  • A different viewpoint indicates that larger wheels may provide higher top speeds, while smaller wheels could enhance acceleration, depending on race distance.
  • One participant proposes that larger wheels might reduce axle friction due to lower rotational speeds at equivalent forward speeds, recommending narrow and hard wheels to minimize rolling resistance.
  • A later post requests a formula to compare the performance implications of using 20" versus 26" wheels, noting a specific course distance.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the effects of wheel size on speed and stability, and the discussion remains unresolved with no consensus reached.

Contextual Notes

Participants do not provide specific formulas or detailed calculations, and assumptions regarding the impact of wheel size on performance factors are not fully explored.

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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