i got a 1992 ford f-150 with a 5.0 and a 5 speed tranny. i have 31's on it now with stock suspension. im going to be putting a 6inch lift on it here soon and looking at putting 35's on it and maybe 37's if they will fit. i got 3.55 gearing right now and i dont know what to goto for the bigger tires.

 

To keep near stock performance and mathematically make up for the difference in tire size, use around 4.10 ratio for 35s and 4.33 ratio for 37s.