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  • CarPro Advice:  The Importance Of The Correct Rear Axle Ratio

    CarPro Advice:  The Importance Of The Correct Rear Axle Ratio

    Not a week goes by that I don’t get a question about the right vehicle with which to tow a trailer with. This is one of two common problems I hear all the time:

    1. My pickup gets horrible fuel economy.
    2. My pickup doesn’t do a good job towing my trailer.

    When I get these questions, I always ask which rear axle ratio the caller has, and I would guess 90% of the time, the caller doesn’t know. People go to dealerships way too often focused on color, comfort, engine size, etc. The rear axle ratio should be at the top of the list, no matter what you are going to use your pickup for. If not towing, you want the best fuel economy you can get, and if you are towing, you want to make sure your truck will do the job.

    Understanding Rear Axle Ratios

    There is good reason automakers offer a variety of different axle ratios. The axle ratio 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. Four-wheel-drive trucks will have a matching ratio in the front axle’s differential.

    Step one in understanding axle ratios is to know what the numbers signify. The lower the number, the better fuel economy, and the higher the number the more towing power you have, but fuel economy suffers. For instance, a 3:31 gets better fuel economy than a 3:73. On the other hand, a 3:73 or perhaps a 4:10 will tow much more, while fuel economy greatly drops. The most popular rear end ratio in trucks today is the 3:55, which sort of averages towing power and fuel economy. This is a good ratio for the occasional towing or hauling individual. For a person who tows more often, and heavier loads, the 3:73 or 4:10 may be more appropriate.

    HubSpot Video

    2023 Ford Super Duty F-250 Tremor. Credit: Ford.

    Much has changed over the past 5 years or so with axle ratios. Today, we are seeing half-ton trucks with 6 cylinder or small V8 engines able to tow close to 12,000 pounds. Not too long ago, you would need to go to a ¾ ton truck with a large V8, V10, or diesel engine. Much has been learned about the effects of rear end ratios in the last decade.

    If you move up to a diesel engine, understand that the power and torque ratings of the engine have a huge effect on the rear end needed. For instance, a 2019 Ford F-350 (Regular or Super Cab) diesel with a 3:31 SRW (single rear wheel) rear axle ratio will conventionally tow 15,000 pounds, but you can go up to 21,000 pounds with the same truck that has a 3:55 or 4:10 DRW (dual rear wheel) rear end.

    Do Your Research

    It is important that you do your own research before truck shopping. Unfortunately, not nearly enough salespeople at dealerships understand rear axle ratios and how they can affect a vehicle’s performance. Generally, new trucks will have the rear axle ratio right on the window sticker. One important note, fuel economy ratings on the window stickers reflect the ratio that comes standard on a particular truck and doesn’t take into account optional ratios. In most cases, trucks are rated with about a 3:55 ratio, so going to a 3:31 and 3:73 will not change what is on the window sticker.

    Trailer-Towing Guides

    The good news is that a quick Google search will find all the manufacturers’ trailer-towing guides. This is why it is important to get your trailer before you get your truck. Find the right truck based on the total weight of whatever you are towing. If it is a travel trailer, make sure you add for contents that go inside. Carrying water, clothes, canned goods, butane, etc. can add a lot of weight. If it is a cargo trailer, what is the most weight you’ll be towing?

    Finally, lean to the upper side. It is better to have too much truck, than not enough, when it comes to carrying loads. 

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    Photo Credit: Ram Trucks.
    This article was last updated January 25, 2023.