click this link http://www.cashershighperformance.com/calulator.html and see if this is right. the oem gearing is 4.4 so change that.

 

It's so damn close that I can't see it making an incredible difference. I have 205/40/17's and compared to stock (i think its 195/55/15) my tire is just a tad larger, and therefore it means I'll be going a bit slower than my speedo says, and I'll actually get more miles than my odometer thinks I'm getting. No big deal if you ask me, it's off by 0.05%, so basically I'll get 5 extra miles per thousand that my odometer reads. Who cares? I'm pretty sure the odometers margin of error is bigger than that anyway.