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What’s the diff?

What’s the diff?

All about truck differentials

Many people buy trucks based on the engine, the styling or the cab layout. But there’s one part hidden underneath a truck that can make a world of difference in how it performs. It’s called the differential.

Pickups are known for being fully customized to fit a particular job, from their cabin size to their bed length and a wide variety of gasoline and diesel engines. One of the most important options when setting up your perfect truck, though, is picking the right gear ratio for the differential.


The differential — often shortened to “diff” in truck parlance — is located directly between the wheels on your truck, and it uses different sizes of gears to adjust how fast the wheels turn in relation to the transmission speed.

The difference between the transmission speed and the wheel speed is determined by the gear ratio in your differential, and it can make a big difference in how a truck performs in ordinary driving and when towing a trailer.


When buying a new truck, you can pick different gear ratios from the factory that will help with your mileage. For trucks that won’t be doing much towing, it makes sense to pick a gear ratio in your differential that results in better gas mileage, although this could hurt your truck’s towing performance.

Likewise, if you do a lot of towing, you’ll want to install a differential that makes it easier to start pulling a trailer at low speeds. This means the transmission will be making more revolutions for each turn of your wheels, though — and that means worse gas mileage.

It’s simply a tradeoff, and you get to decide on the right mixture of efficiency and towing power for your needs.


Another job of the differential is to let the left and right wheels turn at different speeds. Every time you go around a corner, your outside wheels have to make more turns than your inside wheels, and differentials make that possible.

For people who do serious off-road driving, though, it can be a good idea to get a differential that locks both the left and right wheels together. This can help create traction on slippery roads, which is important for extreme off-roaders.

Some new trucks have differentials that will lock electronically with the push of a button. Others require you to climb under the truck and manually lock the differential. Either way, it’s a good option to have on rugged trails.