Is Differential Gearing Worth The Investment?
Modern trucks and SUVs have made fuel efficiency a top priority. As a result of this effort, more vehicles are being outfitted with fairly low numerical gear ratios placed inside of the vehicle’s axle differentials from the factory. Working in part with this numerically low ratio are modestly sized highway-centric tires that help keep rolling resistance to a minimum and RPM’s low. Adding additional weight and increasing the tire size of the vehicle over stock can drastically impact its performance and fuel efficiency.
To correct this issue, you’ll want to swap out your original axle differential gears with a higher numerical set. Because your differential gears work as a torque multiplier, moving to a higher numerical gear ratio will make it easier for your stock powertrain to turn the larger tires. This is not only a proven way to regain performance and fuel economy, but it serves as a more cost effective and reliable option when compared to placing power-adders on your engine. While there are many variables that will determine which is the best gear ratio for your vehicle, we’ve put together a list of the most important things to consider before moving to a new gearset.
The gearsets you’ll be changing are located inside of the axle housings at the front and back of your 4x4. The two main components consist of the ring gear and the pinion. The pinion is what attaches to your vehicle’s driveshaft and rotates the ring gear. Your gear ratio refers to the number of times the pinion rotates to every revolution of the ring gear. So, if your pinion turns 3.73 times to every 1 rotation of the ring gear, your ratio is 3.73:1. This is considered a numerically low gear ratio number.
What Gearing Does
Changing your gear ratio does not add horsepower to your vehicle. What it does is act as a torque multiplier, making the power you already have work more effectively. Think of a higher numerical gearset like moving from a short ratchet drive to a long breaker bar. The higher the gear ratio, the greater the leverage it has to turn the tires.
The Engine Factor
A more powerful engine is going to be less affected by a tire change to a certain extent. This is especially true for diesels that have massive amounts of torque. That’s not to say that a higher numerical gear ratio isn’t needed, but rather the ratio change doesn’t need to be as dramatic for V8 and torque-rich diesel platforms.
The amount of transmission gears you have, along with whether it’s a manual or automatic, makes a substantial difference in picking the correct differential gear ratio. When comparing two potential ratio options, 4.56 versus 4.88 for example, we tend to air on the side of slightly higher numerical gearing in our off-road rigs as it lessens the strain on the transmission.
Elevation & Weight
If you tend to carry a lot of gear or have added a considerable amount of aftermarket parts, be sure to factor that into your gear ratio equation. Elevation should also be considered as higher elevations will zap more power from your engine. If for example you are deciding between a 4.88:1 or 5:13:1 ratio, and your vehicle is on the heavier side or resides at elevation, go with the higher numerical set.
Cost vs Benefit
Swapping out differential gears isn’t something the average person should even consider trying at home. This means you’ll need to rely on an experienced shop and it’s going to likely set you back over $2,000. While this is a serious investment, the fuel economy and performance benefits alone are worth it. When you factor in the reduced strain on your transmission, you may find that this re-gear could save you thousands in repair cost in the long run.
Strength Vs Power
Depending on the axle, you may find that the pinion gets smaller as the gear ratio increases. The pinion on the left is for a 5.13:1 ratio, while the pinion one the right is from a 3.73:1 set. While the 3.73 pinion is larger, the gear reduction benefits of the 5.13 far outweigh any perceived strength loss by the new pinion size. This pinion variance may change depending on what type of differential your vehicle has.
The goal with changing the differential gears is to make the vehicle have the same or better performance as it did from the factory. Though a higher numerical gearset will give back that off-the-line performance you may be craving, too high of a gear will come at a cost. Drag racers have been installing higher numerical gears sets in their cars for decades. Their goal is purely performance driven. If you go with too high of a differential gearset, your vehicles RPM’s will increase drastically on the highway. This will actually hurt your fuel economy. The difference between a 4.88 and a 5.13 is barely noticeable, but 4.56 to 5.29 is pretty extreme.
The number one reason why most people need a differential gear upgrade has to do with tires. Depending on how heavy the tires are, how much rolling resistance they create, and of course, how much taller they are over stock, will all factor into your gear ratio decision. For example, this 37x12.50R17 Nitto Tire Recon Grappler A/T you see here is 10 pounds lighter than a mud terrain in the exact same size. This weight savings equates to less performance lost, making the move to a numerically higher gearset even more effective.
From the factory, your vehicle comes with the gear ratio programmed into the computer. This means you will need some sort of calibration tool that will allow you to input the new ratio into the computer. Doing so will allow the speedometer to read correctly and automatic transmissions to shift properly.
If you perform an online search for recommended gear ratios for your specific vehicle, you’ll likely see gear charts pop up in the search field. Unless the gear chart is specific for your engine and transmission combination (which most are not), don’t rely on them too much. You are always better off consulting with a gear installation expert in your area before purchasing a new gear set for your vehicle.
More From Driving Line
- Want a closer look at gearing benefits for a Jeep Gladiator Rubicon? Watch this video.