What is the Axle Ratio?
The axle ratio is the number of revolutions the driveshaft has to make to produce a single rotation of the axle. This number is usually expressed as the number of rotations it takes over one.
For most trucks, the driveshaft will turn between three and four times for one rotation of the axle, which will be either 3:1 or 4:1.
Your truck has its own set of capabilities and strengths depending on a lot of different factors. The engine, transmission, and suspension will all dictate aspects of your truck’s performance and either help it or hinder it.
However, the axle ratio is one of the most important parts of your truck’s powertrain and depending on how it is set, you can get wildly different driving experiences.
By understanding why axle ratio is important and what it means for your truck, you can pick the perfect setting for you and your driving needs.
Where to Find Your Axle Ratio
Most trucks will have a sticker on the differential that will tell you what the axle ratio is and other pertinent information about the driveline. However, the differential will get hot over a long period and the sticker may fall off or wear away eventually.
If you don’t see the sticker, you can also check your vehicle’s owner’s manual and it should be listed in there. If you don’t have either of these things, you are going to have to get a little more technical and calculate the ratio yourself.
How to Calculate Your Axle Ratio
There are two ways that you can calculate your own axle ratio if you don’t have it in your documentation. If you are mechanically inclined enough to take the cover plate off your differential, you can get it open and take a look at the ring gear and pinion gear. These gears transfer the energy from the engine and the number of teeth on them determines the axle ratio.
The ring gear is the larger one attached to the axle and the pinion gear is attached to the driveshaft. To calculate your ratio, count the teeth on the ring gear and divide it by the number of teeth on the pinion.
If you don’t want to open up your differential, you can get a rough estimate by spinning the wheel. With your truck jacked up and in neutral, make a mark on the driveshaft and turn one of the rear wheels one full revolution. Make note of how many times the driveshaft spins and this will be a ballpark figure for the axle ratio.
Common Axle Ratios
Automakers will pick the stock axle ratios based on the features they want to emphasize. For example, the Chevrolet Silverado has two options for axle ratios: 3.42:1 and 3.23:1.
Both of these are on the more fuel-efficient side but also give you enough power and torque for a reasonable towing capacity. For the most part, you will be fine using the standard axle ratio that your truck comes with unless you are regularly performing heavy-duty jobs or want to gear your truck for the best possible fuel consumption. Knowing some of the most common ratios can help you decide which is best for you.
For Fuel Efficiency:
If you are trying to get the best fuel economy possible for your truck, a lower ratio is a great way to do it. A ratio of 3.15:1 will give you a good mix of better mileage and decent power.
In fact, the Ford F-150, which is considered the best-selling truck of all time, offers trucks with a 3.15:1 ratio at the lowest end of the spectrum.
If you are going to be taking your truck on long trips or using it as your daily driver for hauling groceries, this is a good place to start.
For the Best Towing Capacity:
If you are planning on towing large payloads and have a V8 gas or diesel engine, an axle ratio between 3.55 and 3.73 will be perfect. It should be noted, however, that diesel engines, such as the ones in a Dodge Ram 1500, already tend to have quite a bit of torque, so you may be able to get away with a lower ratio and still tow larger items. You will also be able to keep a lower ratio if you have a new truck that has an eight- or ten-speed automatic transmission. The lower gears in those transmissions will allow you to make up the torque you may be missing from a lower axle ratio.
If you are looking for quicker, more nimble performance, an axle ratio of around 3.55 will be ideal. This will cause the engine to make more revolutions per minute and will require less of the throttle to get up to speed. However, it will result in a lower MPG in both all- and rear-wheel-drive vehicles and will not be ideal if you are going to be using your truck as your daily driver.
Understanding Axle Ratio
The axle ratio, also sometimes called the gear ratio, is determined by the gears in your truck’s differential. This component is located at the rear end of a rear-wheel-drive truck and it links the back axle to the driveshaft, turning a parallel rotation into a perpendicular one.
The engine moves the driveshaft which, in turn, moves the rear axle and wheels. This is how the energy of the engine is transformed into wheel movement and the axle ratio will have a lot to do with how that energy is distributed.
As the first number in the axle ratio goes up, your truck will be using more of the available torque and will be able to do more in the way of towing and hauling. However, the engine will also be running at a higher RPM with a higher numeric axle ratio, so you may lose fuel efficiency. This is why trucks often come with different optional axle ratios.
A lower axle ratio will cause the engine to run at a lower RPM since the driveshaft turns the axle faster. This can result in better fuel economy at highway speeds but the truck will not be as powerful when it comes to towing or hauling. This is why it is so important to know your needs before you start thinking about different axle ratios.
Why is Axle Ratio Important?
The axle ratio is important because it will have a big effect on how your truck runs and what you can do with it. Depending on your needs and what you expect to do, your axle ratio will have to be within the correct range. Since it will heavily determine the engine RPM, it will also affect the amount of gas you use per mile and how your engine performs.
Most automakers choose an axle ratio that works as a happy medium between torque and fuel efficiency. If you have a four-wheel-drive truck, the front axle has a differential that will be set roughly the same as the rear axle ratio. All of these factors will change how your truck drives and what it can do.
What Does Axle Ratio Affect?
The axle ratio affects a few different things when it comes to your truck’s performance and its ability to do certain jobs. Because of this, when you go to the dealership to buy a pickup truck, you should know what you are planning to do with it and what your needs are likely to be when it comes to power, torque, fuel efficiency, and overall performance. Understanding these factors can help you make the right decision.
The axle ratio will have the biggest effect on your fuel efficiency and how economical your engine will be. If you need to have a higher axle ratio for heavy-duty jobs like towing a boat or motorhome, you can expect your engine to burn fuel faster than it would with a lower ratio. You should also be sure to couple this with the fact that the towing payload will be a burden on fuel efficiency as well.
If you are buying your truck as a commuter vehicle or if you plan on taking long trips with no heavy loads and minimal gear, a lower axle ratio might be your best bet. This will get you better fuel efficiency at highway speeds since the engine won’t have to work as hard to turn the wheels. It may also help preserve the components in your engine and make for better longevity in the long run because of the easier workload over many years.
The other major thing that the gear ratio will affect is your truck’s ability to tow and carry large payloads. If you are towing an extremely large payload like a motorhome or anything over 5,000 pounds, an axle gear ratio of at least 3.73:1 is highly recommended. This will allow the truck to start moving the load without having to use as much of the throttle and will also ensure that you have enough torque going to the wheels to pull the load up any hills you might encounter along the way.
Acceleration is another big factor that can be determined by your axle ratio. If you want a truck that has a nimble, quick feel, a higher axle ratio is recommended. Because the engine will be running at a higher RPM, it takes less of the throttle to bring the truck up to speed. On top of this, you also get the benefits of the larger towing capabilities. However, it also means your engine will be working harder to create one turn of the wheel, which will result in worse fuel efficiency. In most cases, finding some kind of happy medium is your best choice.
What to Consider When Choosing an Axle Ratio:
Before you decide on an axle ratio, you will want to think about the gas prices in your area. If you are looking to spend as little money on gas as possible, a lower axle ratio will help you get better fuel efficiency and won’t cause your engine to work as hard as it would with a higher one. Depending on your financial situation and what you will be using your truck for, it may be a good idea to sacrifice some torque for better fuel economy.
How You Use Your Truck:
The right axle ratio for you will also depend on what you plan to do with your truck. If you are an avid outdoors person who regularly carries big payloads and does a lot of towing, a higher final gear ratio is going to be a better bet. This is especially true if you plan on bringing your truck off-road while towing or carrying any kind of large load. You will be glad you have that extra power if you have to drive up a hill or traverse any kind of rough terrain.
Your Truck’s Powertrain:
Depending on the kind of powertrain your truck has, you may not need a high axle ratio to handle tougher jobs or bigger payloads. If your engine already puts out a lot of pound-feet of torque, you may be able to get away with a lower ratio and save yourself a little bit of money on gas. Diesel engines, for example, almost always have higher torque than gas engines, so consider the kind of drivetrain you are going to be working with.
Tire size is an important consideration when it comes to torque and axle ratio. If you have a lifted vehicle with larger tires, this can cause the engine to run at a higher RPM when you are at highway speeds. This is because an automatic transmission will keep the truck in a lower gear to compensate for the added space on the tires. Because of this, you may need to adjust your axle ratio if you are going to be putting larger tires on your truck.
Understanding axle ratio is essential if you want to get the best performance out of your truck. Whether you have a four-, all-, or rear-wheel-drive axle, your truck will need to have the right ratio for the jobs you are trying to do with it. Taking the time to choose the right gearing for your needs when you are buying a truck will help you save money at the gas pump and ensure that you have enough power when you really need it.