I found the size gear I needed by searching the web, I am running a T5, search for your transmission, you will have to measure the height of your tires, their is a formular for figuring the gear size, I found a site that already had it figured for you, but it was for the T5 transmission, I will try to find the site again, and will let you know what it is
http://www.428cobrajet.com/speedo-calc.html here is the site with the calculater for the gear size for the T5 trans
http://www.hanlonmotorsports.com/t5speedo.asp