Gear Ratio ?

[blazin_]

I have an 87 K5. With a manual transmission. The spec for a stock Blazer is 6.55:1 in first gear. How do I find the gear ratio for third gear ? I'm thinking of going to a larger tire. 31x10.50x15R is what I have now. Im thinking of going to 33x12.50x15R. I know may not be completly necessary to change my gears, but it whould be nice to know if I go bigger in the future. I know there is a math formula for this, I just can't remember it.

 

[chris walker]

it should be either (3rd) 1.70 or (4th)1 because you should have a sm465 the 6.55 is the granny first which you dont need to use on the street so you really start in second
you probably have 3.73 or 3.56 gears in your diffs I would change those if you want to go to anything bigger than 33's