Originally Posted by jdetzel
According to here:
There would be about a 6% increase with the smaller tires.
In other words if you traveled 100 miles your odometer would actually show 106 miles.
It actually says 5.833%, which @ 30mpg would show as a 1.7mpg increase.
That is just what that site says, I do not actually know how to do any of the tire size calculations.
Oops I goofed. The factory Michelin PS3s are 235/40
I reran the calc and it said the 16s would now read 2.1% fast. That's pretty negligible IMO (ie, actual speed is 100 km/h but speedo reads 102).
The 18s are way too fat for this car, but they are awesome. My fuel eco definitely is better with the skinnier winter tires on (while it's still not actually winter yet, most days are above freezing still). Maybe when the 18s wear out I might pick up some factory 17s, just to have a hope at actually getting 40 mpg for once :p