I've seen a few other posts, but not sure what to believe. Do adding 18" wheels to a tC slow your car down? I'm a little confused, because if you keep the overall wheel diameter the same, rolling resistance should also remain the same.

Or is the problem from going to a wider (and heavier) wheel when going to the larger diameter? I can see the wider wheel increasing drag and a heavier wheel making a difference.

However, getting a equivalent weight (or lighter than stock) 18" wheel, same overall diameter and only marginally wider (0.5") I think would have no effect. Has anyone timed their car before and after a wheel upgrade?

 

Wider and Heavier and more contact area.

My box went from 33MPG to 29MPG just by switching to bog
chrome wheels.

 

this is goofy... but i don't know much about wheels or tires. i bought my xb with 18" wheels (dealer added). the tires are very low profile. when i replace the tires will i have to stay with very low profile (if i want to keep my 18 in wheels) for them to fit? thanks for your help (and patience with a newbie question) i did search first!