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Gear Ratio Calculator
Build with a plan.
Compare tire sizes, transmission presets and axle ratios side by side. Calculate engine RPM at a road speed, or find MPH at your chosen RPM—before you change parts.
Choose a transmission for each setup, enter your axle ratio and tire size, then select MPH → RPM or RPM → MPH. Use Copy A → B to start with the same vehicle and change one thing at a time.
02 / SEE THE DIFFERENCE
Your gearing, at a glance.
Gearing estimates with no clutch or torque-converter slip. Actual results can differ with an unlocked automatic.
03 / EVERY GEAR. BOTH SETUPS.
Road speed at your RPM.
Each cell compares A / current with B / proposed. Speeds are in mph.
How to read the results & transmission sources
These are gearing estimates, not achievable top speeds or predictions of acceleration, fuel economy or towing capacity. Calculations assume a 1:1 transfer case and no clutch, torque-converter or tire slip. An unlocked automatic will generally run higher RPM at a given speed. Tire diameter varies by brand, load and wear; use measured diameter for a closer estimate.
Presets describe the listed transmission or reference application, not every vehicle from that manufacturer. Confirm your actual transmission and gearset before ordering parts. The library will grow; an unlisted transmission does not mean we cannot work on it.
Speed = RPM × π × tire diameter ÷ (1056 × axle ratio × transmission ratio), with diameter in inches and speed in mph. Metric sidewall sizes calculate a nominal diameter.
Tires, gears and cruising RPM.
How do larger tires affect gearing?
With the same transmission and axle ratio, larger-diameter tires lower engine RPM at a given road speed. A numerically higher axle ratio raises it. Compare your current setup with a proposed tire and gear combination to see the difference.
Which gear ratio should I choose?
Matching cruising RPM is only part of the decision. Vehicle weight, engine characteristics, intended use, transmission and available axle components also matter. These estimates help you start the conversation; they do not determine towing capacity or guarantee performance.
Does this calculator include manual transmissions?
Yes. Choose Automatic or Manual to filter the presets, including truck transmissions and traditional American muscle-car options. Each preset includes its ratios and a source reference. Confirm the exact transmission in your vehicle before choosing parts.
Planning a regear near Baltimore? Explore our differential repairs, overhauls and gearing upgrades in Halethorpe, Maryland, or tell us about your vehicle.
BRING US THE PROBLEM. WE’LL GIVE YOU THE SOLUTION.
Let’s put the right gears in your build.
Tell us about your vehicle, tire size and how you use it. We’ll help you work through the options.
