Mine originally had 16". That was when I researched and found that a 234/40R18 was almost dead even with the 215/55R16. Granted the others are not that much different. I was running a 225/45 and my speedo was off about 3 mph slow at 60. Now I'm running a 245/40, it's slighty shorter and the speedo is off about 2 mph at 60.

 

It's all good... I can't see 3mph difference, have you ever noticed our speedo's are a little hard to see ?? I set the Aeroforce to mph in the SS, so I can see it.....

 

ok cool, well i can get some 225/40's so that should be good enough, thanks !