Why You Should Re-Gear Your Truck or SUV After Lifting It
Adding ground clearance to your vehicle can be more complicated than installing taller tires.
You've decided to lift your truck or SUV by adding larger-than-stock tires, such as those really cool looking 37-inch versions. After the first drive, though, you might ask: Where the heck has all the power gone? The answer might not be the lack of engine power but how it is delivered to those new, taller tires.
Automakers engineer their vehicles to perform with a good balance of torque, speed, and fuel economy based on their factory specifications. When you switch over to larger tires, that balance is upset by their extra height, weight, and rolling resistance. You'll also likely experience slower acceleration.
One solution is to consider re-gearing your vehicle's differential when installing taller tires.
A vehicle's differential transfers power from the transmission to the wheels and tires on either end of the same axle. This allows each tire to rotate independently during cornering, as the inside tire has a shorter distance to cover in a corner and must turn slower than the outer one.
Gears: The Tall and Short of It
Numerically lower differential gears are considered "tall." These are better suited for vehicles that spend the majority of the time on pavement, where top speed and fuel economy are a priority. Many mainstream cars and SUVs have tall gears.
Numerically higher gears are called "short." They're great for drivers looking for quicker acceleration and low-rpm access to the engine's torque and are a commonly upgraded item on trucks designed for frequent towing. However, you'll lose some top speed. (If you see Jeeps with oversized tires doing 55 miles per hour on the highway, the owners have probably changed to a shorter gear set, and the engine's rpms are likely higher.)
Swapping to shorter differential gears will improve your lifted truck or SUV's straight-line acceleration when driving your vehicle off-road or at lower highway speeds.
What Happens When You Re-gear Your Truck or SUV?
As an example, consider the popular off-road 2023 Jeep Wrangler Rubicon with the available V6 and automatic transmission. The midsize SUV has a V6 engine, eight-speed automatic transmission, and 4.10-to-1 differential gears. (This means the driveshaft has to spin 4.10 times to spin the wheels once.) As anyone who's driven a Wrangler can attest, it's adequate on the road in stock form and quite capable off-road.
Jeep offers buyers of a brand-new Wrangler an optional 35-inch tire package — the original tires are about 32 inches — which includes a gearing change among its list of upgrades. The company includes 4.56 gears with the bigger tires, but even shorter 4.88 gears are available as a further upgrade. Without the changes, the stock powertrain would struggle to move the heavier wheels and tires, especially with the corresponding impact to gear ratio with the larger diameter tires.