When it comes to modifying your vehicle for off-road use, there’s a pretty basic list of parts most people consider. Typically, a suspension lift is installed for increased ground clearance and a smoother ride over unpaved terrain, which then allows for larger tires to be installed, providing better traction. Many use this as an excuse to run aftermarket wheels, as well. But when you increase the diameter of your rig’s tires, you may cause some unintended consequences that you might have not have thought about.
While we agree that lifting your vehicle is beneficial and installing larger all-terrain or mud-terrain tires will give you better grip in the elements and make obstacles easier to traverse, you might notice your rig isn’t quite as nimble as it was when it was stock. This is due to a few reasons, such as decreased aerodynamics and added weight, but the biggest factor is the increased rolling distance from the larger diameter of the tires. You may have heard that one way to combat this loss of performance is by regearing your rig. But what does that mean, exactly?
What Are “Gears”?
Your front and rear axles are made up of several parts, but the main function of this crucial piece of drivetrain is to convert rotational energy from the your engine, transmission and driveshaft to the axle shafts and subsequently your wheels and tires, making the vehicle move. This can only be done using a differential, which is itself made up of several parts.
Inside your differential is a set of gears, known as a ring and pinion. The ring gear is a circular shaped gear with diagonal teeth along one side. The pinion gear is shaped like an ice cream cone, with spiral gears wrapped around it. The ring gear is fixed to the left and right axle shafts, and the pinion gear is fixed to the driveshaft. These two gears, when meshed together, transfer the direction of the energy from a spinning driveshaft to a spinning wheel.
What Is a “Gear Ratio”?
These gears have a ratio, meaning for every single rotation of the pinion gear, there are several rotations of the ring gear. The reason for this is to allow your tires to spin much faster than your driveshaft, lessening the revolutions per minute (rpm) on the engine and transmission. This ratio is typically written out in numerical form, such as 3.73, 4.56 or 5.13. It is inferred that these ratios are actually 3.73:1, or 3.73 to 1, meaning for every single rotation of the driveshaft, the wheel will rotate 3.73 times.
What Does “Regearing” Mean?
Regearing a vehicle is the act of changing the gear ratio of the ring and pinion gears inside the differentials. In off-road applications, this is typically done on both the front and rear differentials, and the new gear ratio is a lower ratio than the stock ratio, to help increase the performance of the rig.
For example, pretend you just bought yourself a new Jeep Wrangler Sport. It comes from the factory with 3.73 gears and 32-inch tires. Now imagine you’ve installed a suspension lift and 37-inch tires, and you can immediately feel the effects of the larger diameter tires on your rig. It’s slower to takeoff, the automatic transmission seems to always be “hunting” for the right gear to stay in and you notice decreased performance going up hills. What do you do? One of the best methods for getting some of that power back is to regear the differentials to a 4.88 gear ratio. Now, instead of 3.73 rotations, your wheels will rotate 4.88 times per single rotation of the driveshaft. And if you’re thinking that’s not a big change, remember that over the distance of a mile, that can make a huge difference.
What Are the Benefits of Regearing?
Regearing your rig after installing larger tires will make an immediate difference in the performance of your rig. You’ll feel more power upon takeoff, it’ll get up to speed sooner and you’ll feel more power when climbing steep obstacles. Many off-road enthusiasts also report better fuel economy in city driving, as the engine doesn’t need to work as hard to get the vehicle rolling from stop light to stop light. Regearing can even help your automatic transmission feel like it did when the vehicle was stock and prevent it from “hunting” for the right gear.
What Are the Negative Effects of Regearing?
While there are many benefits to regearing, you’ll want to be aware of some of the reasons people don’t regear their differentials. First off, it’s expensive. Differential gears are very precise components to any vehicle, requiring a professional installer who has years of experience regearing vehicles with specialty tools most mechanics don’t have. It’s also time consuming. For this reason, this job is rarely ever attempted at home, and almost always trusted to the pros, making it an expensive mod. Many shops will charge $1,500 or more to regear front and rear differentials, and that may not even include the cost of the parts themselves. You have to be absolutely certain that the benefits of increasing your rig’s performance is worth the cost of this mod. However, most will find this mod as money well-spent.
Another con to regearing your rig is increased cruising RPM. Because of the new, lower ratio, your engine will be spinning faster than before. For example, if your engine would sit at 2000 RPM at 70 MPH on stock 3.73 gears, and you then regear your rig to 4.88 gears, you might find your engine now turns 2700 RPM at the same speed. This can hurt your highway fuel economy, so be prepared for that.
How Do I Know What Gear Ratio to Run?
Knowing what gears to run is highly dependent on your vehicle, your driving style and how big of a change you’ve made in tire size. Going from a 32-inch tire to a 40-inch tire would require a much more drastic gear ratio change than going from a 32-inch to a 35-inch tire. Different transmissions have different internal gear ratios, so the same vehicle with a manual transmission might require a different gear ratio than the automatic version with the same size tires. If you plan on towing with your rig, this could be a factor to consider as well. And while there are some gear ratio calculators out there on the internet, consulting with your local off-road shop expert is the best course of action to determining which gear ratio is right for you.
We hope this article arms you with the knowledge to make an informed decision when it comes to changing your rig’s gear ratio. Whether you’re planning a build, tired of your existing rig feeling sluggish on and off the pavement or looking to regain a few MPGs, regearing can be one of the best modifications you make to your off-road vehicle. While it’s expensive and time consuming, many have reported that it made them fall in love with driving their big, heavy off-road vehicle all over again. And that’s a mod you can’t put a price on!