Sorry it took so long for a reply. Haven't had access to a computer for a while. It threw the speedometer off by +/- 3mph, however, gas mileage didn't seem to suffer. If anything, it helped. I average between 19-21 mpg in the city and 25 mpg on the interstate if I behave. Not bad for 115,000 miles. Ride quality didn't suffer at all. There is slight road noise, but at 50mph or higher. Nothing bad at all.