I decided to post in LT1 Tech instead of Wheels and Tires cause this is not exactly a wheel brand or tire brand specific question. Anyway, I'm gonna go from a 26.1" tall tire to a 24.5" tall tire. How much will this affect my gear ratio?

 

Alright, I found my answer on an fbody gears calculator website. Just so you guys know, switching to a 1.5" shorter tire means I will shift from 2nd to 3rd at 94mph instead of 100mph. (I have an A4 2.73 gears)

 

As you discovered, it's just the ratio of the tire diameters:

24.5/26.1 = .9387 or 100 x .9387 = 93.87 or 94 mph

26.1/24.5 = 1.065 or 2.73 x 1.065 = 2.91, so it acts like you changed axle ratios to 2.91.

 

yay.....2.91 gears for me instead of 2.73's!!!! hehe jk

 

That also means your speedo will be off by that much too... unless you get the PCM "fixed"

 

yea....guess I'm gonna have to get madwolf to gimme a new internet tune