Diff Gear Ratio Calculator

Tire Size & RPM Solver

$1.99 · Designed for iPad. Not verified for macOS.

Calculate diff ratio from tire size, RPM, and speed. 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.

Ratings & Reviews

  • This app hasn’t received enough ratings or reviews to display an overview.

Added a More Pro Tools section to discover related field calculators.

Version 1.0.2

The developer, Shanghai Sheyuan Network Technology Co., Ltd., indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .

  • Data Not Collected

    The developer does not collect any data from this app.

    Privacy practices may vary, for example, based on the features you use or your age. Learn More

    Accessibility

    The developer has not yet indicated which accessibility features this app supports. Learn More

    Information

    Seller
    Shanghai Sheyuan Network Technology Co., Ltd.
    Size
    924.7 KB
    Category
    Utilities
    Compatibility
    Requires iOS 17.0 or later.
    • iPhone
      Requires iOS 17.0 or later.
    • iPad
      Requires iPadOS 17.0 or later.
    • Mac
      Requires macOS 14.0 or later and a Mac with Apple M1 chip or later.
    • Apple Vision
      Requires visionOS 1.0 or later.
    Languages
    English
    Age Rating
    4+
    Copyright
    © 2026 Sheyuan Inc.
  • Developer Website
  • Privacy Policy

    • Supports

    • Family Sharing

      Up to six family members can use this app with Family Sharing enabled.

    More by Shanghai Sheyuan Network Technology Co., Ltd.