Tire Size and Gear Ratio Chart

The size of the tires on your vehicle can significantly impact it's fuel efficiency, handling, and even the accuracy of the speedometer. While gear ratios in the vehicle's transmission determine how well the engine's power is transferred to the wheels [source: Warner]. Modifying either component can substantially alter the vehicle's dynamics, which is why these calculations can be so important.

This gear ratio and tire diameter chart is meant to give you an approximation of ideal RPMs at highway speed (65 mph) for three situations: fuel economy, every day driving and increased towing power. This chart provides values that represent a 1:1 ratio on a manual transmission. Gear ratio and tire diameter charts are ideal for making your car as efficient as possible [source: Morley].

Note: automatic transmission RPMs tend to be a little higher and transmissions with an overdrive tend to be a little lower.

Making the right adjustment to your vehicle's gear ratio can significantly enhance performance when you change tire sizes. To do so, follow the following steps:

You can tailor the setup of your vehicle to suit new tire sizes, while maintaining or enhancing its performance, efficiency, and drivability, by following the steps we touched on above [source: Rogers]. Remember, while website DIY guides are helpful, they can't replace professional expertise. So don't be afraid to ask a local auto shop before you begin tinkering.