Towing is serious business for truck owners. It can be a major deciding factor in a pickup purchase. However, the axle ratio is a little-known spec that can drastically change a truck’s towing capacity. Anyone consistently pulling a trailer, boat, camper, or anything else should familiarize themselves with this often overlooked number.

What is axle ratio?

Truck shoppers have a lengthy list of options to consider. Cab size, bed length, engine size, and trim level all impact how well a truck will perform at various tasks. Axle ratio is an important consideration for anyone whose primary concern is towing capacity.

The phrase axle ratio described the number of rotations required to turn the wheels one full rotation. Therefore, the axle ratio is expressed with two numbers, such as 3.21:1. The first is the number of driveshaft rotations and varies. The second is the number of wheel rotations. As such, the second number is always one.

A typical pickup truck is sold with a standard axle ratio with optional increases. For example, the 2021 Ram 1500 is sold in three axle ratios, 3.21:1, 3.55:1, and 3.92:1. Each one affects the truck’s towing capacity. The reasons why make perfect sense with a little bit of insight.

How axle ratio impacts towing capacity

Edmund’s guide to axle ratios cites the Ram 1500 for figures. The standard 2021 Ram 1500 axle ratio of 3.21: has a maximum towing capacity of 8,230 pounds. Increasing the axle ratio to 3.55:1 pushes the towing capacity to 9,930. Why does increasing axle ratio boost maximum towing capacity?

Higher RPMs directly impact the number of axel rotations it takes to turn a wheel 360 degrees. As a result, increased engine spinning improves pulling power while towing a heavy load. As such, the highest axle ratio trucks have the highest towing capacity. For example, pushing the Ram 1500’s axle ratio to 3.92:1 adds 3,100 pounds of towing capacity over the standard ratio.

High axle ratio trucks take a slight hit to their fuel economy. As a result, drivers can expect to see a one to two mpg drop in fuel economy. However, if towing isn’t a primary concern, the standard axle ratio is probably fine for most buyers, so an unnecessary axle ratio upgrade is a mistake.

Get the best axle ratio for you

Typically, light and heavy-duty trucks are sold with optional axle ratio upgrades. Sometimes these are stand-alone addons, but they can be included in towing packages as well. Towing packages often represent a better value to buyers and include helpful extras like hitch connectors, bigger radiators for improved cooling, and even heavier springs.

Truck shoppers should carefully consider their needs before investing in one of these pricey upgrades. Being “over trucked” isn’t always worth the hike in price and loss of fuel economy. In general, axle ratios between 3.55:1 and 3.73:1 are more than capable.

Newer eight, nine, and ten-speed transmissions perform well with higher axle ratios. Lower first and second gears in newer transmissions mean an offset of acceleration deficits at higher axle ratios. Offsetting that deficit means taking less of a hit at the pump.

Truck buyers looking for the most towing power for their buck should carefully consider the axle ratio that best suits their purpose. Choosing too low means missing out on power. Picking too high could hike up fuel spending with no return.

RELATED: The 5 Best Trucks for Towing According to U.S. News