I have an 07 HHR LS, stock 16" wheels and tires..

I have a chance to buy a set of cobalt SS rims and tires (18").
I have read alot of people on this board up sizing to a different tire size. How would that affect the speedo or milage if I switch. I know I had a firebird, i had to flash the PCM if I moved to certain sizes. ( plus 1 or more. )


Any info would be greatly appreciated.

 

Check this site and book mark it. You can plug in different sizes and find how it will affect the speedo http://www.web-cars.com/math/tiresize.html

 

If the overall height is the same, no problem. Otherwise, it will change odometer and speedometer.

I upsized and had the bcm changed.

 

Post pics after. I like Cobalt wheels on the HHR.