33, 35, 37, 38, 39, 40, 42, or 54 inch tires? Doesn't matter this method works for them all. If you use your factory gear ratio for the base number then your speedometer will be accurate instead of off by 5-15mph.
My stock Ratio is 3.73 Dana 30 My stock Wheels are 29 I installed 33s I did the Maths and resulted 4.24 I found the 4.10 and 4.56 ring and pinion kit Witch one would be best fit for my set up ???