Q: I have a 1991 Ford Mustang LX couple with a bone-stock 302.
I’ve always thought about getting an 8.8-inch ring and pinion set for my Ford, but I’m having difficulty picking one out. There are so many choices in ratios, but I can’t quite get a grip on what they all mean—can you help me tell the difference between them?
A: Before sinking your teeth into a rear-gear swap, it’s important to know how gear ratios will affect your Mustang’s driving behavior and overall performance.
Rear gear ratios are determined by dividing the number of teeth on the ring gear by the number of teeth on the pinion. For example, a 43-tooth ring gear divided by a 10-tooth pinion gear yields a ratio of 4.30:1, or, the pinion rotates 4.3 times for every one rotation of the ring gear.
Once you have your ring-and-pinion’s ratio, multiply it by any of your transmission’s gear ratios to determine the final drive ratio in that gear—lower final drive ratios provide lower cruising rpm and slower acceleration, while higher ratios will make for quicker takeoffs at the expense of greater rpm at highway speeds (which also increases engine wear).
For a stock Mustang, a lower-ratio ring-and-pinion, like one of these 3.55 Mustang gear combos will provide a good all-around performance boost without taking away from everyday streetability.
If you’re planning on taking your pony to the track, a higher-ratio gear set would be a better fit.