So I'm in the very very early stages of getting new wheels for my G37S. At this point I have neither the money nor any specific wheels in mind, but I do have a question regarding wheel size. I know many of you have aftermarket wheels on your car(s) and figured I'd get a better answer here than anywhere else.

If I get bigger wheels than stock - say 20" instead of the stock 19s on it now - will I need to have anything besides the alignment checked/calibrated? My dad was telling me that I would have to take it to the dealership and have them do something with the tacho/speedo or it wouldn't read accurately because of the different size wheel. I've never heard this before, and he's a bit behind the times in general.

Thanks.

 

Depends on what size tires you get. You'll need lower profile tires to keep the accuracy of the speedo in check if you go with bigger wheels.

I think tirerack.com has a pretty good explanation on how it all works and I bet they could suggest which tires to get too.

 

When you go up in wheel size, you go down in tire wall - the circumference should stay +/- 5% from the old one, so that the wheel and tire stays the "same". Unless you're building a monster truck, never ever put on any sort of wheels you have to recalibrate anything for.

For example; if your current wheels are 235/40/18 you can put on 235/35/19, and the circumference changes, um ... *grabs calculator* .... 0,2 inches. Not noticeable on your speedo and perfectly fine.

 

They are correct. If you want a clear explanation on it google "wheel plus sizing" or better yet check out

Tire Tech Information - The Plus Concept

 

Thanks guys, that makes a lot of sense. Completely forgot the rubber would make a difference.

Thanks, knowing what to look for makes it easier to google it

 

Use this handy dandy calculator when determining if your tire sizes are within acceptable rolling diameters

Tire Size Calculator - tire & wheel plus sizing

Speedo's are NOT easily recalibrated to my knowledge. And an re-alignment is not necessary if you're just changing out wheels/tires. Suspension changes (i.e springs/coilovers), on the other hand, do require one.