I am looking to upgrade my stock 15" Mazda 3 wheels to a set of the 17" OEM wheels since i am gonna get a good deal from a friend. How is this going to effect performance, gas milage, ride quality, and spedometer reading?? any help would be greatly appriciated!!!

 

1) performance really should change at all...if the rims are lighter, which i doubt it, there will be a very, VERY slight increase in acceleration (i heard somewhere that removing 1 lb of wheel weight is like removing 10 lbs of vehicle mass)
2) gas mileage should stay the same
3)ride quality may be a bit bumpier, since your riding on less tire (my old civic had 17's, and you felt every bump, but i kinda liked that)
4) if the tire size stays the same, your spedometer wont change at all....
id only be worried if you owned a truck, and you were putting 38" tires on it....

 

Thanks man!

 

oh, typo... in #1, it should say "performance really shouldnt change at all"...
however, handling will definetly improve because the tires wont flex nearly as much.
for example, on your current 15's, when taking corners quickly, your tire will tend to flex... (this is normal).... putting larger wheels on will eliminate this...