Multi-Gear Speed Calculator
Paste a list of gear ratios and see a complete speed-by-gear table at one engine RPM.
How to use this calculator
- Enter one engine RPM that represents the operating point you want to compare, such as redline or a chosen shift RPM.
- Enter the final-drive ratio and tire diameter that apply to every gear in the transmission.
- Paste transmission ratios from first gear onward as a comma-separated list, for example 3.50, 2.19, 1.41, 1.00, 0.83, 0.72.
- Read the table vertically to see theoretical road speed in each gear at the same engine RPM. Large gaps between consecutive rows indicate larger RPM drops after an upshift.
- For a before/after comparison, keep the engine RPM and transmission ratios fixed and change only tire diameter or final drive so you can see which variable caused the change.
Formula and assumptions
For every entered gear, wheel RPM = engine RPM ÷ (gear ratio × final drive). Road speed = wheel RPM × tire circumference after unit conversion.
GIIRR calculates idealized geometry and kinematics. Friction, slip, compliance, tire deformation, manufacturing tolerances and control-system behavior can move real measurements away from the theoretical result.
Worked example
Suppose redline is 7,000 rpm, final drive is 3.90 and tire diameter is 25.7 inches. With ratios 3.50, 2.19, 1.41, 1.00, 0.83 and 0.72, GIIRR calculates six theoretical speed points. Re-running the same transmission with a 4.30 final drive lowers every speed row by the same proportional amount and makes the effect of the axle-ratio change immediately visible.
Frequently asked questions
Can I enter more than six gears?
Yes. The tool accepts a reasonable comma-separated list of positive numeric ratios, so conventional multi-speed transmissions can be compared in one table.
Can I compare two transmissions?
Yes, but run each ratio set separately and keep RPM, final drive and tire diameter identical. That prevents other variables from hiding the difference in transmission spacing.
Does the table show the RPM after each shift?
No. It shows speed in each gear at one chosen engine RPM. To estimate post-shift RPM, compare the ratio of the old gear to the new gear at the same road speed.
Should I use redline?
Only if that is the question you are investigating. A lower chosen RPM can be more useful for cruise or shift-strategy comparisons.
Why is theoretical top-gear speed often unrealistic?
Gearing only establishes the speed-to-RPM relationship. A vehicle may lack the power to reach the chosen RPM in top gear because aerodynamic drag rises strongly with speed.
For safety-critical, legal or fitment decisions, verify the result against manufacturer documentation and physical measurements.
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