Picking The Right Axle Ratio For Your Pickup


Image
A recent caller to the Car Pro Show was unhappy with the fuel economy of his truck. 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.

Automakers Offer Variety of 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.

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.

Photo Credit: Ford
Stuart Watson
Jerry-- I have a 2019 Ram with the Hemi engine. The CarPro dealer salesman discussed the axle ratio with me, and I told him I wanted good mileage, because I don't tow trailers. I cannot remember what ratio he gave me. So my question is, how can I find out what axle ratio my truck has? Maybe put in the VIN number on some website you know about? Thanks
The Car P.
On the driver door when you open it is a tag. There will be a rear axle code there, and you can google rear axle codes for 2019 Ram 1500s. It's actually quite easy. Let me know if you have any trouble.

Jerry Reynolds
Aufait
Now that several manufacturers are offering the 10 speed transmission I have heard you can step down one size differential and get the same towing capacity than you could in tbe past and reap the fuel economy when not towing. This being due to a very low 1st and 2nd gear. I realize you can check the manufacture literature for towing information but do you feel this is generally the case?
The Car P.
Good to hear from you. Honestly, I don’t see any evidence to back up what you are saying. I stress the importance of looking at the automaker’s charts to make sure you get the right axle. I didn’t see any major change in towing capacity when F150 went to a 10-speed.

I would never choose an axle ratio with max capacity or or even near what the factory says is adequate.

Jerry Reynolds
.
Jerry, as a member of one of the Dodge RAM Cummins forums, I see these same complaints all the time about poor fuel economy and poor towing ability. A great deal of the time, you aren't getting the full story. Like, the truck owner drives around like their hair is on fire, and they can't figure out why the fuel economy is so poor compared to some other guy's truck. Or, they have a 6-inch lift and 40" tall tires and didn't update the computer or gearing to compensate, so they get terrible fuel economy and the truck wouldn't pull the hat off your head. And, many times the truck owner just has unreasonable expectations, like..."How come my truck only gets 10 MPG towing but gets 22 when not towing! WHY is the towing fuel economy so bad???" My 2015 RAM 2500 2WD pickup with the Cummins and auto trans, regularly tows as much as 14,000 pound trailers with ease, and when not towing gets over 20 MPG on the highway with ease. It's all stock original, and I drive very reasonably, and it meets my expectations in full. RAM doesn't offer any optional gear ratio on the single rear wheel diesel models, my truck has the stock 3.42 gearing and it is adequate to the task. It now has 465,000 miles on it.
The Car P.
I totally agree, i hear it all also and on a regular basis. People ask me often about towing 12,000 pounds but want great mileage when not towing. You have to choose to a certain degree. You are correct that driver habits are the biggest factor. You also have to remember, the MPG you see on window sticker is an estimate that was arrived at under perfect conditions with no air conditioning, and it all happens in a laboratory, not in real world driving.

Thanks for listening to the show.

Jerry Reynolds
.
I can't tell you how many times over the last several years I've heard people call in on Jerry's show, myself included, complaining about the fuel economy on their EcoBoost F150. When the EcoBoost first came out, Jerry used to say that you had to get 20,000 or so miles break in and the mileage would improve. I've got an F150, 3.5 liter EcoBoost with a 3.55 axle and have never ever gotten better that 15MPG average. The window sticker states 15 city, 21 highway. I've heard a lot of people call in complaining about their mileage not being what's stated on the window sticker.

The Car P.
No question about it. if you want the mileage stated on the window sticker, you can get it, but you have to really try with very slow starts, no more than 65 miles per hour on the freeway. A head wind can change everything, under-inflated tires can affect mileage as well.

Remember, too that these are EPA ESTIMATES, arrived at under perfect conditions in a laboratory.

The one constant is if vehicle #1 is rated at 20 combined, and vehicle #2 is rated at 22 combined, neither vehicle may get there, but vehicle #2 will get 2 miles per gallon more.

Also important, all pickups and SUVS EPA estimates are rated with a middle rear axle ratio, usually a 3:55, and the vehicle may have a 3:73 or 4:10, which has a big affect.

Jerry Reynolds