LaunchnRetrieve

What does axle ratio mean?

3.31 vs 3.55 vs 3.71

Milton6001

The higher the number the bigger the better for towing. If you need to know more than that google what it means. People could write books on the subject.

3.73 is the best for towing regardless of which engine you have. 3.55 is decent, and 3.31 is for people who do not plan to tow and want the best highway MPG.

LaunchnRetrieve

I'm guessing the mpg ratings are based on the lowest available axle ratio.

acadianbob

Basically it means the number of times the driveshaft rotates to 1 revolution of the rear axle. The higher the number, the more rpm the motor spins for the same road speed. Higher numbers generally mean better power but less gas mileage. If you tow larger trailers for longer distances, you might need a 3.55 or 3.73. If you run empty or light a lot, go for a 3.31 or 3.15. You have a 6 speed transmission so you could always run in 5th or 4th gear on a 3.31 or 3.15. It all depends on your situation.

sargetom203

I tow my 25' travel trailer (approx 6,000# loaded) witht the 5.4 V8 and 355 rearend and the 6 spd....and it does great. Several articles I have read in truck or trailer publications seem to indicate that the dfference between 373 and 355 is pretty much minimal and not really noticeable. Can't really say, since I have only towed with this 355, inthe F150 line. I had a Dodge with 410 and that was a whole different ballgame.

byoungblood

You have to make a fairly significant jump between ratios to obtain a noticeable difference in fuel economy and how well the engine handles a load. 3.55 vs 3.73 is more or less a wash with both (really depends on the transmission gearing), whereas going from 3.31 to 3.73 will give a significant difference in performance and mileage.

Generally the smaller the number, the better the mileage on the highway will be. Shorter (numerically larger) ratios can sometimes actually get better mileage around town. From a towing/hauling perspective, a numerically higher ratio may keep the engine in its power band better without having to constantly downshift while cruising.

When buying a truck, or any vehicle for that matter, pay attention to the final ratio if you have several to choose from. Swapping ring and pinion gears is not trivial after the fact. What little you may save in gas vs having to regear your truck (multiply the cost by 2 if you have 4 wheel drive) from not doing it right the first time will be wiped out quickly.

zx12-iowa

I've had 3.55 and 3.73 ratios. Towing heavy I noticed a difference in power with 3.73 shifting down less and pulling hills a bit better. Mpg empty, the 3.55 is a mpg better. 3.31 likely another mpg better. Not sure what ratio they use for EPA mpg rating.... With the new 6 speed transmission and low first gear axle ratios, while still important, are not as significant an issue as they were with the old 4 speed transmission.

schmenke

Careful with the use of the word “power”.

The axle ratio does not directly affect the engine power output.
It will affect the final torque applied to the wheels which in turn affects the engine rpm required to maintain a given speed.

For a given speed, the engine rpm will run higher for, say, a 3.73 ratio axle as opposed to a 3.15 ratio. This is why fuel consumption is affected.

mcfarmall

I think youngblood was referring to keeping the engine rpms in the zone of the engines power curve where the torque is highest.

acadianbob

I have 3.73s. At 60 mph, it is only turning 1,650 RPM. Most engines are not producing a lot of torque at that RPM. The Ecoboost is an exception because of the turbos. My point is, if you tow a lot or heavy, you'll be towing in 4th or 5th if you have a lower numerical rear end. That's not necessarily a problem. I'm just saying, think about your RPM at road speed when choosing your gearing and thinking about how you use your truck.