Not necessarily - the speedo reading is dependant on the diameter/circumference of the TIRE. It has no relationship to the rim size.

 

Not true. It will depend on the size of the tire you use. Throw on 16's with a tire the same heighth as the 18's and the speedo will be the same.

 

i have 205/55/16 on similar regular steel wheels during winter as someone posted earlier. ugly as hell, but reason is that is currently cheapest tire size over here and it does not throw so much in speed.speedo off just one mile or two.

hhr has same lug pattern as in cobalt, and here in europe it was easiest to find Opel steel wheels.

 

For the record, the Borbet LV5 17" wheel is one of the few 17s which clear the front Brembo brakes. I have these as my winter set just in case I upgrade to Brembos in the future.