You need to take into consideration the tire diameter tooo.... (not just R&P X torque)
emsvitil,
What data are looking for? Tire size is calculated. Yes, changing tire size will change the effective final drive ratio.
Example: 4.10s, 28" tires, then swapping tire size to 31", effective gear ratio will then be 3.70:1 - higher geared.
Gnarls.