i am thinking to put the 18" WHEELS ON, BUT I'VE BEEN TOLD THAT THE MILEAGE RUNS FASTER, EXAMPLE : IF I DRIVE A ONE MILE DISTANCE, IT WILL REGISTER ON THE ODOMETER AS A 1 1/4 MILE OR SOMETHING CLOSE, IS THAT TRUE?????
DOES ANYBODY HAVE AN ANSWER TO THIS !!!!!
PLZ HELP ME OUT !!!!!!!

 

yes, it is a little bit different but nothing to worry about. You won't even notice the difference.

Some tuners, like the diablo predator can adjust your speedo for tire size and gears if you are concerned.

EDIT: Assuming you are already running 17"

 

as long as your tires are the same overall height as the ones you are already running. so basically, if you have a 17" rim right now and are going to 18" then just get a little bit lower profile tires, not much though. your speedo and all that wont be off then, or at least not niticably. i just got new rims and tires and they are about an inch taller, and my speedo is about 1-2 mph over when im running 60.