Enter your Tire Width, Aspect Ratio, and Wheel Size alongside your Ring Gear Teeth, Pinion Gear Teeth, Target Speed, and Engine RPM to calculate your Differential Gear Ratio — plus your Tire Diameter, Circumference, Revolutions per Mile, and Actual Speed at Target RPM.
Differential Gear Ratio
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Calculated Tire Diameter
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Tire Circumference
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Tire Revolutions per Mile
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Actual Speed at Target RPM
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The differential gear ratio is the number of times the driveshaft rotates for each rotation of the wheels. It's calculated by dividing the ring gear teeth by the pinion gear teeth (e.g., 41÷10 = 4.10:1).
Lower numerical ratios (3.08:1) provide better fuel economy and higher top speeds, while higher ratios (4.56:1) offer more torque multiplication for better acceleration and towing capability.
Yes, larger tires effectively make your gear ratio numerically lower, reducing acceleration and torque. Installing a numerically higher gear ratio can restore performance lost from larger tires.
You can find your gear ratio stamped on the differential cover, in your owner's manual, or by counting ring and pinion gear teeth. Some vehicles have a build sheet in the glove box with this information.
The ring gear is the large gear attached to the differential case, while the pinion gear is the smaller gear connected to the driveshaft. The pinion gear drives the ring gear to transfer power to the wheels.
Yes, this calculator shows your actual speed at a given RPM. For optimal fuel economy, most engines perform best between 1,800-2,200 RPM at highway speeds.
The calculation is very accurate for standard tire sizes. However, actual tire diameter can vary slightly between manufacturers and tire models, so measure your actual tire for the most precise results.
If you change tire size, yes. The speedometer reads based on driveshaft rotations, so larger tires will make it read slower than actual speed. Some vehicles allow speedometer recalibration.