About this app
Changed tire sizes and need to know what diff ratio keeps your RPM in the sweet spot? Diff Gear Ratio Calculator finds the required differential ratio for any tire, speed, and RPM combination — so you pick the right ring and pinion before you buy. Enter tire dimensions (width, aspect ratio, wheel diameter), engine RPM, vehicle speed, and transmission ratio. Get tire diameter, circumference, revolutions per mile, and the exact diff ratio you need. WHAT IT CALCULATES: - Overall tire diameter from metric tire size - Tire circumference in inches - Revolutions per mile - Required differential ratio for your RPM and speed target - Actual speed at a given RPM (with known diff ratio) - Actual RPM at a given speed (with known diff ratio) DRIVETRAIN INPUTS: - Engine RPM - Vehicle speed (mph) - Transmission gear ratio - Transfer case ratio (for 4WD vehicles) TIRE SIZE INPUTS: - Tire width (mm) - Aspect ratio (%) - Wheel diameter (inches) OPTIONAL KNOWN DIFF RATIO: Enter your current or planned diff ratio to see speed-at-RPM and RPM-at-speed calculations. Compare before and after a regear or tire swap. Built for automotive enthusiasts, 4x4 builders, and drivetrain shops. Works completely offline — no internet required.
Latest release
What’s New
Added a More Pro Tools section to discover related field calculators.
Audience growth
Ratings growth
Baseline captured. Growth appears after the crawler observes a changed rating count.
Momentum comes from crawler snapshots for the tracked storefront. “Viral growth signal” means unusually fast recent rating gains; it is an indicator, not download data.
Price tracking
Price intelligence
First snapshot captured. The trend line starts after the next crawler price observation.
- First observed Oct 2, 2026 · 7:51 PM $1.99
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