What Is Axle Ratio?

Although axle ratio may seem like a complicated topic, it’s pretty easy to comprehend once you have a basic understanding of how it works. Depending on whether you are looking at a front-wheel drive, rear-wheel drive, all-wheel drive, or four-wheel drive vehicle, the axle ratio is going to be an important aspect. Whether you need more power for hauling or off-roading or would rather have better fuel economy, then the axle ratio can make a big difference. For four-wheel-drive rigs, axle ratio is typically the same in both the front and rear. However, many automakers will offer the ability to upgrade the rear axle ratio for better acceleration. If you’re shopping around for a new pickup truck, axle ratio is a critical component to consider before making a purchase.

What Is Axle Ratio?

Axle ratio is the number of revolutions the output shaft or driveshaft needs to make in order to spin the axle one complete turn. The number is expressed in a ratio, which represents the number of teeth on the ring gear divided by the number of teeth on the pinion. For example, a truck with a 3.73:1 gear ratio means that the driveshaft will turn 3.73 times for each complete wheel spin. Many people simply refer to the axle ratio as 3.73 rather than express it as the ratio 3.73:1. However, they both mean the same thing.

How to Calculate Axle Ratio

In order to calculate axle ratio, you would count the number of teeth on the ring gear as well as the number of teeth on the pinion. Divide the number of teeth on the ring gear by the number of teeth on the pinion in order to determine the axle ratio of a truck.

If you don’t want to take apart your differential, then here’s a quick “Tech Tip” for you! Most modern differentials will have a sticker located on the outside, so you can easily have access to your axle ratio information. If you have an older vehicle or the sticker peeled off, then there’s another relatively simple way to calculate your axle ratio. Grab a marker and mark the inside of the tire along with the driveshaft. Put the vehicle in neutral while it’s lifted in the air and pin the wheel one full revolution to see ‘roughly’ how many revolutions the driveshaft spins. While this will just give you a ballpark figure, you can estimate the axle ratio by judging the choices available. For example, some of the gear ratios for the Ford F-150 include 3.15, 3.31, 3.55, 3.73, or 4.10. If you count 4 revolutions, then you probably have a 4.10 axle ratio.

Why Is Axle Ratio Important?

Axle ratio is important because it helps determine how much towing capacity, torque, or fuel-economy a truck is going to get. A vehicle with a higher numerical axle ratio will have more towing capacity. However, with the added towing capacity comes decreased fuel economy and a lower top speed. A smaller axle ratio will increase fuel economy but lack the additional torque and power.

Picking the right axle ratio all depends on what you plan on using your truck or rig for. Do you plan on frequently off-roading and need a higher amount of torque at slower speeds? Or maybe you don’t really need any extra power but would rather have a more fuel-efficient vehicle. Some automobile manufacturers allow you to upgrade to a different axle ratio depending on your needs. For instance, the JL Wrangler Rubicon has 4.10 axle ratios in the front and rear, which is different than the 3.45 axle ratios found in the less expensive Sahara and Sport editions.

Many off-road enthusiasts choose to upgrade their axle ratios for performance benefits. However, there are some downsides to going larger when it comes to axle ratio. Although having a higher numerical axle ratio will give you more power, it will affect your top speed as you won’t be able to go as fast. Even though you may not be able to go as fast, you will have better initial acceleration. Along with decreased top speed numbers, having a higher axle ratio will also hurt your fuel economy. Because your engine’s RPMs will be higher, fuel consumption will increase. In addition to higher RPMs, the differential will take longer to complete a full rotation, which adversely affects gas mileage as well.

Should You Upgrade Your Axle Ratio?

An important factor to consider before upgrading your axle ratio or purchasing a vehicle with a larger axle ratio is your hauling needs. If you need to be able to haul a heavy trailer for work or any other reason, then you may want to think about upgrading your axle ratio as it will give you more torque and better pulling power. For daily-driving rigs, a lower axle ratio number might be enough to suit your needs and can save you money on fuel. If you’re unsure, you can always opt for the smaller axle ratio and purchase aftermarket ring and pinion gears to upgrade your axle ratio in the future.

Sources: How to Choose the Right Axle Ratio for Your Pickup Truck, Edmunds | What Is the Difference Between 3.55 and 3.73 in Ford Trucks?, It Still Runs | Image Credit: Jeep, Toyota

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