Are stock 17's with the stock run flats smaller,larger , or the same size over all diameter than going with 18's. Reason I ask is I'm going to get 18's , but it will be awhile before I lower it. I just dont want it to look stupid just running 18's if there's going to be some huge wheel gap. If so , I will just wait and it all at the same time. Thanks

 

Depends on the tire size you choose. Without tire sizes, we can't know whether your 18's will be larger or smaller than stock diameter.

Unless you're talking about ordering the factory 18s which come with tires that are near the stock diameter.

 

The wheels will be JCW 18" double spokes with 205/40/18 tires. So , that's about the same diameter as the stock ones?

 

See how it's done @ Tire Rack

[205mm x 40%] x 2 + 18in = 24.5"

[205mm x 45%] x 2 + 17in = 24.3"

Close enough.

 

it's when you to 215/35/18 that things get a little smaller (23.9" in my case). But that's a lot bigger than a 215/40/17 which was about 23.5" I can't believe it was nearly a full inch smaller than a JCW wheel. Woah.