Altering your axle ratio can have significant benefits at the track, on the trail, and at the pump. This ratio measures how many times the driveshaft must turn for the wheel to turn one time (e.g., if you have 3.73 gears, the driveshaft must rotate 3.73 times for the wheels to turn once). A numerically-higher gear ratio acts like a longer wrench for your engine – making it easier for it to turn the wheels and ultimately transmitting more power to the wheels.
Changing your ring and pinion gears to a numerically-higher ratio can improve acceleration and make it easier to tow a large payload. It can also restore lost performance caused by oversize tires on lifted trucks. A stock or lowered vehicle will respond well by going one or two steps higher. E.g., if your truck has a 3.55:1 axle ratio, the next two common ratios to consider may be 3:73:1 and 4.10:1. Keep in mind that the higher the ratio, the higher your RPM will be when cruising – but going from 3.55:1 to 4:56:1 would be a bit extreme for a stock or lowered truck in terms of cruising RPM and the subsequent drop in fuel economy.
When changing the gear ratio on a four-wheel drive or all-wheel drive truck, it is necessary to replace the ring and pinion gears in the front and rear. Otherwise, severe damage to your driveline will occur.
When trying to determine what gear ratio would compensate for a change in tire diameter, a simple way to calculate it is as follows: (new tire diameter) / (old tire diameter) x (current gear ratio) = (new gear ratio) Example, changing from 31.9" to 35" tires on a vehicle with 4.10 gears would look like 35 / 31.9 x 4.10 = 4.50 In this example, a 4.50 gear ratio would restore most of the lost performance. From there, look at what ratios are available for your axle and you can choose to go a little higher or lower depending on what's available.