What gear ratio do I need for 35 inch tires?

To effectively compensate for 35-inch tires and restore your vehicle's power and performance, selecting the appropriate gear ratio is crucial. Generally, for 35-inch tires, recommended gear ratios typically range from 4.56 to 4.88, depending on your vehicle's engine, transmission, and intended use.

Why Re-Gearing is Essential for Larger Tires

Installing larger tires significantly alters your vehicle's effective gearing. A larger tire completes fewer rotations per mile than a smaller one, which effectively makes your original gear ratio "taller" (numerically lower). This can lead to:

• Loss of acceleration and reduced power: Your engine works harder to move the vehicle.
• Increased strain on the engine and transmission: This can lead to premature wear and overheating.
• Reduced fuel economy: The engine struggles to maintain speed, often requiring more throttle.
• Difficulty maintaining speed: Especially noticeable on inclines or when towing heavy loads.

Re-gearing involves installing new ring and pinion gears in your differential(s) to achieve a numerically higher gear ratio. This helps to bring the engine's RPM back into its optimal power band, compensating for the larger tire diameter.

Factors Influencing Your Ideal Gear Ratio

The "best" gear ratio isn't a one-size-fits-all answer. Consider these key factors:

• Engine Size and Type:

  • V6 Engines or Smaller: Often benefit from numerically higher (lower) gear ratios like 4.88 or even 5.13 to compensate for less inherent torque.
  • V8 Engines: Might perform well with 4.56 or 4.88, offering a good balance of power and highway manners.
  • Diesel Engines: Known for producing high torque at lower RPMs, some might tolerate slightly lower numerical ratios, but still require significant re-gearing for 35-inch tires.

• Transmission Type:

  • Manual Transmissions: Offer more direct control, and some drivers prefer slightly lower numerical ratios if they are comfortable with more shifting.
  • Automatic Transmissions: Modern automatics with more gears (e.g., 8-speed, 10-speed) can sometimes handle slightly taller gearing due to their wider range, but proper re-gearing is still vital. Older 3- or 4-speed automatics often demand numerically higher ratios to stay in the power band.

• Intended Vehicle Use:

  • Daily Driving/Highway Use: While still needing aggressive gearing, some might opt for the lower end of the recommended range (e.g., 4.56) to maintain slightly better highway RPMs and fuel economy.
  • Off-Roading/Rock Crawling: Higher numerical ratios like 4.88 or 5.13 are often preferred for improved torque, control, and reduced strain on the drivetrain at low speeds.
  • Towing Heavy Loads: Similar to off-roading, higher numerical ratios (4.88, 5.13) are crucial to move heavy loads efficiently and safely, reducing transmission temperatures and engine strain.

Recommended Gear Ratios for 35-Inch Tires

Here's a general guideline for common applications:

Understanding RPM Implications

When selecting a gear ratio, it's helpful to consider its impact on engine RPM at various speeds. For instance, with 35-inch tires and a numerically lower gear ratio such as 3.31, your engine speed would be approximately 2065 RPM at a typical highway cruising speed. While a 3.31 ratio might be suitable for stock tire sizes in some vehicles, it is generally insufficient for 35-inch tires, leading to the issues mentioned above (poor acceleration, strain). Re-gearing aims to bring your engine's RPMs back into a more efficient and powerful range for the larger tire size.

Professional Installation is Key

Changing gear ratios is a complex process that requires specialized tools and expertise. It involves precise measurements and adjustments to ensure proper meshing of the new gears. Improper installation can lead to premature wear, noise, and component failure. It's highly recommended to have gear changes performed by a qualified automotive technician.