Axle Ratios Explained Nicely

A BRIEF INTRO

Axle Ratios, which are sometimes called Final Drive Ratios, in short are just the ratio of turns of the driveshaft to turns of the wheel. The ratio can be roughly determined by doing drivehaft turns to wheel turns, for example, a 3.75 ratio would be 3 and 3/4 drivehaft turns for one turn of the wheel. The correct way to identify the ratio is to divide the ring gear teeth by the pinion teeth; for example, 41 ring gear teeth to 11 pinion teeth would be 3.73 (41/11 = 3.73).

WHAT'S THE RING AND PINION?

Inside the differential, there is a ring gear and a pinion gear.

• The driveshaft spins the pinion.

• The pinion spins the ring gear, which is attached to the axle.

Take a look at this sick GIF showing them work.

Ring and Pinion in Action (Courtesy of Spicer)

There is a lot more going on in the differential, enough for a whole other article; here is a photo that includes the differential.

WHAT DIFFERENCE DOES IT MAKE?

We're glad you asked. Typically, a higher ratio is going to make the engine able to apply more torque to the wheels than a lower ratio. However, a lower ratio allows the engine to keep a low RPM at highway speeds, increasing fuel mileage.

• High ratios (3.9+) are typically going to be found in high-performance vehicles, dragsters, trucks, semis, among other similiar vehicles. These higher ratios allow these vehicles to apply more torque to the wheels, allowing them to do what they do.

• Low ratios (3.3 or lower) are typically going to be found in fuel-efficient vehicles like sedans, hatchbacks, small SUVs, among other similiar vehicles.

DO PEOPLE SWAP THEM?

All the time, modders will increase the ratio number by swapping rear ends. Truck owners may also do this to achieve a higher towing/hauling maximum. Most of the time, this actually ends up being an entire axle swap, as most of the time that is much easier and more effecient than swapping the axle internals; it's also incredibly possible the components won't fit in your axle.