Q:

How do you choose the correct rear axle gear ratio?

A:

Quick Answer

Choose the correct rear axle gear ratio by considering the towing and driving conditions in which the vehicle must perform. Regular towing requires increased power provided by higher gear ratios, while higher speed and urban driving benefits from lower or standard rear axle gear ratios.

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Full Answer

Higher rear axle gear ratios provide increased power to the drive wheels during the drive cycle, which provides increased towing capacity. This increase in power causes increased gas consumption, whether or not under load, and adversely affects the fuel economy published by the Environmental Protection Agency for the vehicle, which uses the factory-standard gear ratio for its calculation.

Vehicle manufacturers use different tire sizes, which affects the gear ratio calculation and makes comparisons across brands difficult. Edmunds recommends rear axle gear ratio comparisons only among vehicles of a common brand because manufacturers have not universally adopted the standard rating system published by the Society of Automotive Engineers.

Transmission specifications can affect towing capacity independently of the rear axle gear ratio. An increase in the number of gears in the transmission generates more power, which results in greater towing capabilities. Knowledge of this fact allows the comparative evaluation of vehicles that have different gear ratios but provide similar towing capacities.

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