Upgrading to larger diameter wheels and tyres is a popular modification for improving off-road traction and performance. However, the increased wheel size can throw off critical drivetrain gear ratios engineered for stock tires. To maintain optimal acceleration, torque and engine efficiency, re-gearing the differentials and/or transfer case is recommended.


Why Gear Ratios Matter

Stock gear ratios are precisely matched to the tire diameter and torque characteristics of the engine. Mounting significantly larger tires without recalibrating gear ratios lowers the final drive ratio. This forces the engine to work harder to rotate the increased tire circumference, straining components and hampering acceleration.


Symptoms of incorrect gear ratios with larger tires include:

  • Excessive RPMs at highway speeds, increased engine wear
  • Sluggish acceleration and lack of low-end torque
  • Reduced fuel economy and towing capacity
  • Overheating and premature failure of drivetrain components


To counteract the gear ratio reduction from bigger tires, popular re-gearing options include:

  • Lower numerically higher numerically ring and pinion gearsets in differentials to raise axle ratio. A 4.56:1 ratio is common for 33" to 35" tires
  • Two-speed transfer case gear reductions like advanced Rock Crawler boxes from Advance Adapters. These provide extra low crawler gears
  • Complete axle housing upgrades to already re-geared units like the Ford 9" and GM 14 Bolt
  • Combination of the above - for example, 4.56 gears front and rear plus 4:1 low range transfer case


Considerations for Re-gearing

  • Desired off-road capabilities and terrain. Rock crawling needs lower gear ratios than higher-speed desert driving
  • Tire diameter - larger tires require more aggressive re-gearing to compensate
  • Engine power and torque characteristics. High-torque diesel engines need less aggressive gears than lower-torque gasoline engines
  • Vehicle use is like towing and highway driving. More radical gear ratios reduce highway drivability


Consulting a specialist is wise to select optimal gear ratio upgrades. Properly calibrated gearing ensures adequate torque for off-road use while maintaining reliable highway manners and engine longevity. With the right gear ratios, you can confidently conquer the trails without overtaxing your 4x4.