How to Choose the Right Axle Ratio for Your Pickup Truck

When you're shopping for a pickup truck, in addition to different motor, transmission, torque and driveline choices, you might see different axle ratios offered as options and wonder which one to choose. You might also wonder if the gearing really makes an all-around difference. For many truck buyers who won't be doing any heavy-duty work or don't expect to regularly carry a hefty load, the standard axle ratio gearing will probably work fine. But if you plan to pull a trailer or haul heavy loads, it's a good idea to understand what the axle ratio is and how that ratio affects your truck's performance and all-around fuel economy, even when the truck is unladen or driven at low speed.

If you plan to do a lot of highway driving in your pickup, the standard axle ratio will generally give you the best fuel economy by lowering the number of revolutions per minute (rpm) the engine turns for each turn of the axle or axles. Lower rpm means the engine doesn't have to work as hard to move your truck down the road.

Understanding Axle Ratios

Automakers build trucks with a range of optional axle ratios. The term refers to the gears in the truck's differential, which is a mechanical device that links the rear axle to the driveshaft and then the engine. Technically, the number should be expressed as a ratio, such as 3.55:1, meaning the drive shaft turns 3.55 times for each turn of a wheel. But that gear ratio would most commonly be referred to as "3.55" or simply "three fifty-five."

The key to understanding gear ratios is to remember that, as the numerical ratio goes up, towing capacity increases but fuel economy goes down. A numerically higher axle ratio provides a mechanical advantage to send more of the engine's available torque to the rear tires (and front tires, in a four-wheel drive vehicle), but you pay the price at the fuel pump.

So, a truck with optional 3.73 gears will tow a heavier trailer than one with 3.55 or 3.21. But it will also use more fuel in all situations because the engine's rpm will be higher. For example, Ford says the 2018 F-350 Super Duty 4x2 regular cab pickup equipped with the 6.2-liter gasoline engine can tow up to 16,700 pounds when fitted with a 4.30 axle ratio but just 13,200 pounds with the numerically lower 3.73 axle.

Four-wheel-drive trucks will have a ratio in the front axle's differential that closely matches that of the rear axle. Unless the truck's window sticker lists an optional axle ratio, it will come with a standard ratio that's selected by the manufacturer.

Standard Axle Ratios

The standard axle ratio for Chevrolet pickup trucks is chosen to balance performance, capability and fuel economy, according to the company. The standard ratio also is biased more toward fuel economy. By selecting a final drive ratio that lowers engine rpm under most conditions, manufacturers can more easily meet government mileage standards. In contrast, optional axle ratios tend to provide more towing capability by increasing the amount of available torque delivered to the axles.

If you are constantly towing, the highest axle gear ratio possible is what you're after. The choice of a numerically higher axle ratio will only knock off about 1 mile per gallon from the truck's fuel economy. But since pickup truck fuel efficiency is low to begin with, even a 1 mpg reduction is significant.

The "drive cycle," which is how fast and where you drive, is also an important consideration when selecting the right axle ratio, according to truckmaker Ram. For lower speeds and rural driving, a higher gear set will add capability and a more spirited driving experience without too much damage to the final mpg number, according to Ram. But if you do a lot of high-speed driving, you might want to consider a vehicle with a numerically lower gear set to decrease engine rpm and improve fuel economy.

Axle Issues to Consider

One tricky thing about choosing an axle ratio is that the EPA fuel economy information on the window sticker primarily applies to the "base" or standard axle ratio, even though that particular truck might come with an optional axle ratio, says Dan Edmunds, director of vehicle testing for Edmunds. Therefore, any axle ratio you see listed on the options side of the window sticker will lower the fuel economy figures printed on the very same sticker.

Another difficulty is that optional axle ratios, and their effects on towing, cannot be compared across truck manufacturers, Dan Edmunds says. That's because each truckmaker may use a different tire size, and the tire itself acts as the final "gear" in the system. It's best to compare the axle options within a single brand to see how each one affects the tow ratings listed in that brand's towing guide, he says.

As you shop for your truck, you might hear axle ratios with lower numbers referred to as being "tall" gears and those with higher numbers as "short" gears. To more easily remember what this means, think of a tall person who travels a greater distance with each step. Similarly, a tall gear moves the truck farther with each turn of the engine. Trucks with tall gears deliver better gas mileage because their engines turn fewer rpm at a given road speed. But taller gears also reduce the torque — or power — so you can't tow heavier trailers or haul heavier loads.

Ram and other manufacturers recommend that truck shoppers look at the towing and payload tables on their websites. They're there to help customers select the right powertrain for their specific needs. As truck manufacturers produce transmissions using more gears, the axle ratios will also change. For example, a transmission with more gears might allow a truckmaker to offer a taller rear axle ratio (a 3.55 instead of 3.73) and still provide improved towing and hauling capabilities.

Before you leave for the dealership, take a moment to think about how you're going to use the truck. When in doubt, default to a higher numerical axle ratio. While it will lower your fuel economy slightly, it will also mean you will be more comfortable while hauling and towing over long distances.

But if your concern is getting better fuel economy at highway speeds, a numerically lower drive-axle ratio might be right for you, as could a transmission with more gears.