Does my speedometer need adjusted if I increase my rim size? if so, how?
AudiWorld Uber User
Joined: Mar 2000
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What oldfarts4 is trying to say is no, provided...
you adjust the size of you tire accordingly. The rim size can change, however the overall diameter must stay the same. This is done by reducing the sidewall height of the tire.
For instance, stock A4 tire size is 205-55-16.
Going to a 17" wheel, you would use a 225-45-17 tire (which I believe is within +-1% of the rolling diameter of the stock tire).
Sidewall height is 205mm * 0.55 = 112.75mm (16's)
vs. 225mm * 0.45 = 101.25mm (17's)
Now if you get a tire size that does not maintain the rolling diameter of the tire, your speedo will be affected.
For instance, stock A4 tire size is 205-55-16.
Going to a 17" wheel, you would use a 225-45-17 tire (which I believe is within +-1% of the rolling diameter of the stock tire).
Sidewall height is 205mm * 0.55 = 112.75mm (16's)
vs. 225mm * 0.45 = 101.25mm (17's)
Now if you get a tire size that does not maintain the rolling diameter of the tire, your speedo will be affected.
AudiWorld Uber User
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Wait a minute! What's wrong with my math?
There is NO way the sidewall height on my stock 16's are 113mm!!! That's getting into SUV range!! Just eyeballing my car it looks more like 90mm on a stock 16" tire!
AudiWorld Uber User
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If you're talking about an A4 (probable since you say 15 to 17)...225-45-17...
unless you want a wider tire...then you'll have to ask one of the other guys. Rubbing gets to be an issue with *some* tires when you step up to 235's. The 225 size is perfect, and that's what Audi put's on the S4 17" rims.
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