Why You Must Re-Gear Your Truck or SUV After Lifting It. You’ve decided to upgrade your truck or SUV with larger-than-stock tires, such as the cool-looking 37-inch models. After the first drive, you might wonder where all the power went. The solution may not be a lack of engine power, but how it is transmitted to those new, taller tires.
Automakers design their vehicles to have a good combination of torque, speed, and fuel economy based on factory specifications. Larger tires disrupt that balance due to their increased height, weight, and rolling resistance. You will most likely feel slower acceleration.
A vehicle’s differential sends power from the transmission to the wheels and tires at each end of the same axle. This allows each tire to rotate independently while cornering because the inside tire has a shorter distance to traverse and must turn slower than the outside tire.
GEARS: THE TALL AND SHORT OF IT
Lower differential gears are considered “tall.” These are better suited for vehicles that spend the majority of their time on the road, when top speed and fuel efficiency are important. Many common vehicles and SUVs have tall gears.
Higher numerical gears are referred to be “short.” They’re ideal for drivers searching for faster acceleration and low-rpm access to the engine’s power, and they’re a popular improvement on vehicles built for regular towing. However, you will sacrifice some top speed. (If you see Jeeps with big tires going 55 mph on the interstate, the owners have presumably switched to a shorter gear set, and the engine rpms are likely higher.)
Shorter differential ratios increase your lifted truck or SUV’s straight-line acceleration when driving off-road or at lower interstate speeds.
WHAT HAPPENS WHEN YOU RE-GEAR A TRUCK OR SUV?
Consider the popular off-road 2023 Jeep Wrangler Rubicon, which comes with an optional V6 engine and automatic transmission. The midsize SUV features a V6 engine, an eight-speed automated transmission, and 4.10-to-1 differential gears. (This means the driveshaft must spin 4.10 times to turn the wheels once.) Anyone who has driven a Wrangler can attest that it is adequate on the road in stock form and fairly capable off road.
Jeep offers owners of a brand-new Wrangler an optional 35-inch tire package — the base tires are roughly 32 inches — that includes a gearing change among other enhancements. The firm supplies 4.56 gears with the larger tires, but shorter 4.88 gears are also available as an option. Without the modifications, the stock drivetrain would struggle to move the heavier wheels and tires, especially given the higher impact to gear ratio with the larger diameter tires.
There are gearing charts available online that will help you identify the appropriate ratio for your vehicle and tire size. Re-gearing your vehicle or SUV is expensive and will likely void at least some of your factory warranty. However, it will lessen stress on your drivetrain and improve your rig’s performance.