After lifting your truck or SUV, you almost always step up to a larger wheel and tire size to complement the new beefy look. When increasing the tire diameter from the factory size, it will have a major effect on your engine's performance. Due to the increased tire diameter, the optimum engine RPM range will be moved effecting your vehicles shift points and drivability.
We rolled over to 4Wheel Parts in Riverside, California, where Brian Gardiner, their driveline and gear specialist, disassembled an '07 Toyota 8-inch rear differential with factory 3.73 gears and replaced them with Genuine 4.56 gears, shims, and bearings. The Tacoma had already received an RBP 6-inch coilover stage II lift and a set of Pro Comp 305/70R18 35-inch tall tires that replaced the factory 245/75R16 30-inch tall tires. Because of the increased tire diameter, the Tacoma's 4.0L V-6 engine RPM was reduced, lugging the engine out of its optimum torque and horsepower range. To increase the Tacoma's engine RPM back to its optimum torque and horsepower range, a taller ring and pinion gear set was installed to the third member of the rear differential to reclaim the torque, power, and drivability. Using the chart in this story, we determined the Tacoma would need new 4.56 gears to reclaim the lost power.