That's a good idea to just run taller tire for driving around on the street. I could put a 275/60-15 on it for driving on the street and then use my 27" tires for the track.

I found this forumula online also.

Tire Diameter x RPM / (336 x mph) = Gear Ratio

IE: 27 x 5500 / (336 x 90) = 5.13