How does axle ratio affect mpg

At a given speed, and if all else is equivalent, a higher gear ratio axle -- again, a lower number -- will have a positive effect on fuel economy. The effect is generally minimal and will account for less than a single mile per gallon, and typically the gains are generally seen at highway speeds.

Additionally, the fuel economy gains or losses from an axle ratio change may be directly offset by the transmission selected. The transmission gearing directly affects the fuel economy at a given speed. The engine's rpm and fuel consumption are generally lower in higher gears. For example, a transmission with four standard speeds operating at 55 mph may see a rpm difference between a high and low axle ratio, whereas a transmission equipped with an overdrive may only see a rpm difference between the same two axle ratios.

The gear ratio is not only affected by the axle, but also the tire size. But choosing the right axle ratio does make a difference in how a pickup performs, be it empty, towing a trailer or hauling a heavy load in the bed. Axle ratio also affects fuel economy on the open highway. When it comes to fuel economy, look at the axle ratio as the amount of fuel burned over a given amount of time when the truck is running at highway speeds.

For example, a truck with a 3. Likewise, a 3. How much better mpg? In general, about. The larger the axle ratio number, the quicker the truck will accelerate. For example, a truck equipped with 3. Similarly, a pickup with a 3. In general, the best towing axle ratio for most of the post pickups is in 3. A small gear will drive a large gear more slowly, but with a greater amount of torque.

A large gear will turn a small gear quickly but with low torque. A typical commercial tire turns about revolutions per mile. Different axle ratios change the number of teeth in the pinion, which is connected to the driveshaft, and the ring gear attached to the wheel end drive through the axle differential. The gear ratio, Kwasniewski says, is the number of teeth on the ring gear divided by the number of teeth on the pinion.

For example, 3. By dividing those numbers, you get an axle ratio of 3. Operations that spend a lot of time on the Interstate running consistent speeds tend to be most drawn lower numeric ratios but transmission type — direct drive or overdrive — engine rating, desired road speed and tire size can all dictate which axle ratios work best. Across 40k tandem rear applications, axle ratio choices generally range between 2.

For on-highway linehaul, the range tightens to a fuel friendly 2.