Tonight I got some 2004 stock 17" Audi rims and tires to replace my 15". How far will that throw my speedometer off? Is there a way to reset my car with the new rims and tires with my vagcom so that it will not be off? Thanks!!!

 

Depends on the tire size. Use a 225-45-17 and you'll be almost identical.

 

I'll ask the question, can you use vagcom to adjust for a change in tire size?

 

http://www.miata.net/garage/tirecalc.html

Go to this site and enter your old tire size and the new tire size and it will tell you how much (if any) it will be off.

 

No you can't. As "krazzz" said, use that url to find the most approximate size to keep same stock wheel diameter.

 

Plus One to what krazzz posted. It's all about the rolling diameter. If the difference is small enough then you don't really need to worry. However, if the difference is large enough you might want to consider having your speedometer re-calibrated.