What size wheels and tires will need the transmission regeared

## Transmission Regearing: Impacts on Wheel and Tire Size

### Understanding Transmission Gears

A transmission’s gears are designed to optimize engine power output for different vehicle speeds. Each gear has a specific gear ratio, which determines the ratio of engine RPM (revolutions per minute) to wheel RPM.

### Impact of Wheel and Tire Size Changes on Transmission Gearing

Changing the size of the wheels and tires affects the final drive ratio, which is the overall gear ratio from the engine to the wheels. A larger wheel or tire requires the drivetrain to turn more times to cover the same distance. This can result in a higher or lower final drive ratio.

### Determining Gear Regearing Requirements

When changing wheel and tire size, it may be necessary to regear the transmission to restore the optimal final drive ratio for the vehicle’s performance. The following factors need to be considered:

1. Original Final Drive Ratio: Determine the original final drive ratio of the vehicle.
2. New Wheel and Tire Size: Calculate the new effective rolling radius of the wheels and tires.
3. Desired Final Drive Ratio: Determine the desired final drive ratio for the new wheel and tire size.

### Formula for Calculating Regearing Needs

New Transmission Gear Ratio = Original Final Drive Ratio x (New Wheel Radius / Original Wheel Radius)

### Examples of Regearing Requirements

Example 1: Changing from 265/75R16 tires to 285/75R17 tires

Original Wheel Radius: 32.6 inches
New Wheel Radius: 34.1 inches
Original Final Drive Ratio: 3.73
New Transmission Gear Ratio: 3.73 x (34.1 / 32.6) = 3.87

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Example 2: Changing from 235/60R18 tires to 255/55R19 tires

Original Wheel Radius: 28.5 inches
New Wheel Radius: 29.5 inches
Original Final Drive Ratio: 3.08
New Transmission Gear Ratio: 3.08 x (29.5 / 28.5) = 3.18

### Impact of Regearing on Vehicle Performance

Regearing the transmission can have the following effects on vehicle performance:

Improved Acceleration: Lower gear ratios can provide better acceleration at the cost of higher RPMs at cruising speeds.
Increased Towing Capacity: Lower gear ratios can increase towing capacity, but may reduce fuel efficiency.
Fuel Efficiency: Higher gear ratios can improve fuel efficiency, but may reduce acceleration and towing capacity.
Speedometer Accuracy: Changing the tire size can affect the accuracy of the speedometer. Proper recalibration may be necessary.

### Choosing the Right Gear Ratio

The ideal gear ratio depends on factors such as:

Type of vehicle: Off-road vehicles and heavy-duty trucks often require lower gear ratios.
Driving habits: Aggressive drivers may prefer lower gear ratios for improved acceleration.
Tire size: Larger tires require higher gear ratios.
Gearing limitations: Some transmissions may not be able to accommodate certain gear ratios.

### Professional Installation and Calibration

It is essential to have a qualified mechanic perform transmission regearing to ensure proper installation and calibration. The following steps are typically involved:

1. Removal and Disassembly of Transmission: The transmission is removed from the vehicle and disassembled to access the gears.
2. Gear Replacement: The old gears are replaced with new gears of the desired ratios.
3. Reassembly and Installation: The transmission is reassembled and installed back into the vehicle.
4. Calibration: The speedometer and other sensors may need to be recalibrated to account for the new gear ratios.

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## Conclusion

Changing the size of wheels and tires can impact the overall performance of a vehicle. By considering the original final drive ratio, new wheel and tire size, and desired performance characteristics, the appropriate transmission gear ratio can be determined. Regearing the transmission is a complex process that should be performed by a qualified mechanic to ensure proper installation and calibration.

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