How to Read the Gear Ratio on Cars

Gear ratio is based on the number of teeth of specific gears.

Gear ratio refers to the correlation between the numbers of teeth on two or more gears that are meshed together. Count the number of teeth on the gear that exerts the force, known as the pinion. Next, count the number of teeth on the idler gear, which is the gear that is moved. Take the second number and divide it by the first number and that is the gear ratio. Gear ratio can be expressed as a fraction or as a decimal.

Instructions

1. Determine if there is a fractional gear ratio or a decimal number gear ratio. If it is a decimal ratio, than that is the number of turns the pinion must make to move the largest gear in the engine.

2. Divide the top number of the fraction by the bottom number. The resulting decimal number is the gear ratio of your smallest gear to your largest.

3. For clarity, consider the following example. Your pinion gear has eight teeth and your largest gear has 32 teeth. The gear ratio could be expressed as 32/8 or 4. It means that for every four rotations of the smallest gear, the largest gear rotates one time.

Tips & Warnings

• Higher gear ratios mean more power. A 4.56 is higher than a 2.37. The higher gear is referred to as "deeper," whereas the lower gear ratios are considered "taller." Taller gears are best for cruising and fuel economy while deeper gears are best for power and torque.

References

• Dictionary.com: Gear ratio

Resources

• "Hotrodders Bulletin Board": How to read gear ratios
• "Offroaders.com": 4x4 related calculators