After recently putting on my 18"s from my 17"s i had my friend pace me, and i was 10 mph slower than his spedometer. (mine said 70 when his said 80) for example. I knew that this can happen w/ bigger tires/rims and such, but a 10mph change, i was just wondering cuz it seemed like a huge change. I thought it was just a little change? Could that be right?