Choosing the Right Diff Ratio For Your Wheels and Transmission
Bigger tyres, a different gearbox or a towing job can all leave your gearing wrong. Here is how to pick a ratio that puts things back where they should be.
A diff ratio that suits the factory tyres and gearbox can feel completely wrong once you fit 33 inch tyres or swap in an overdrive transmission. Getting the ratio right brings back the acceleration and keeps the engine in its happy range on the open road.
Working out what you need
Start with the factory ratio and tyre size, then scale the ratio by the change in tyre diameter. A 10 percent bigger tyre wants a ratio roughly 10 percent numerically higher to keep the same effective gearing.
Other things to consider
Towing wants a numerically higher ratio for pulling power. A cruiser with a tall overdrive can go the other way. Run the numbers through our ratio calculator, or send us the details and we will recommend one.
