I've been inspired recently by the HP vs. Torque and tire/wheel threads. So I put together a comprehensive list of questions that, when answered, should cover all the info you would want about wheels and tires in relation to performance. I will attempt to maintain it in the future on my own website, or perhaps get it accepted as part of the MINI2 FAQ collection.
I know very little about wheels and tires so far, so I need everyone's help! Contribute what you know! Please, be honest - this is for posterity.
Performance and Handling
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Property: Total Weight (Wheel + Tire)
Effect: I have heard that tire weight drastically reduces performance. I have also heard that it affects handling in some fashion, but I'm not sure how. Exaggerating bumps and pockets?
Property: Total Diameter (Wheel + Tire)
Effect: Increases top speed, decreases torque and therefore acceleration. Increases size of contact patch, and therefore traction and acceleration.
Property: Sidewall Height (Tire)
Effect: Increases stickyness of tire (better performance), decreases handling.
Property: Width (Tire)
Effect: Increases traction, and therefore performance. Not sure how it affects handling.
Q: Why, if at all, would you want differntly sized tires in front and back.
Compatibility
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Q: What size tires can go with what size wheels?
Q: How do you determine if a combination of wheel and tire will work on a specific car?
Q: What do the different tire ratings mean? (all the marks that don't refer to dimensionsal data)
Research
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Q: What are the best sites for getting technical data on wheels and tires (including weights)?