📘 AI Summary: Gear ratio calculator: compute engine RPM at any speed for each transmission gear. Input custom gear ratios, final drive, tire diameter. Used for differential swaps, overdrive planning.

Gear Ratio & Speed Calculator

Tool description: Determine engine RPM at a given vehicle speed, or find speed at a given RPM. Supports up to 5 speeds plus overdrive. Perfect for classic Mustangs, Camaros, MGBs, and vintage motorcycles.

Tire Diameter (inches):

Final Drive Ratio (rear axle):

Transmission Ratios (comma separated, e.g., 3.35,1.93,1.29,1.00,0.80):

Calculate:

Vehicle Speed (mph):

Engine RPM:

Why Gear Ratio Matters

Changing rear end gears or tire diameter directly affects acceleration and cruising RPM. Use this tool to avoid over-revving on the highway or losing low-end torque. Formula: RPM = (MPH × GearRatio × FinalDrive × 336) / TireDiameter.