Automotive Calculator

Tire Speed Calculator

Calculate vehicle speed from tire diameter, overall gear ratio, and engine RPM for gearing checks, cruise planning, and drivetrain setup.

Estimate road speed from engine RPM, gearing, and tire diameter

Tire diameter (in)Overall gear ratioEngine RPM

133.99

Vehicle speed (MPH)

215.64

Vehicle speed (KPH)

87.96

Tire circumference (in)

720

Revolutions per mile

Formulas

Tire circumference = π × tire diameter

Revolutions per mile = 63,360 ÷ tire circumference

Speed = (RPM ÷ gear ratio) ÷ revolutions per mile × 60

Reference note

Use total tire diameter and overall gearing for a quick estimate. Real-world speed can vary slightly with tire growth, pressure, and load.

How to use the tire speed calculator

Enter tire diameter in inches so the calculator can determine tire circumference.

Enter the overall gear ratio, using the current transmission ratio multiplied by the final drive ratio.

Enter engine RPM to see the estimated road speed, tire circumference, and revolutions per mile.

Tire speed formulas

Road speed comes from tire circumference, wheel revolutions, overall gear ratio, and engine RPM.

Tire circumference = π × tire diameter
Revolutions per mile = 63,360 ÷ tire circumference
Speed = (RPM ÷ gear ratio) ÷ revolutions per mile × 60

Tire speed examples

28 in tire, 3.73 overall ratio, 3,000 RPM

About 67.0 MPH

Useful when checking cruise RPM or highway gearing.

26 in tire, 4.10 overall ratio, 6,000 RPM

About 113.1 MPH

Helpful for a quick drag-strip or shift-point estimate.

Gearing notes

Use overall gear ratio: transmission gear multiplied by final drive ratio.
Actual speed can differ slightly because loaded tire diameter changes with pressure, load, and tire growth.
Compare setups with the same RPM target when judging tire or gear changes.

Helpful for gearing and cruise-speed planning

Useful for tire and gear comparisons

Good when you want to know how a tire change or gearing change affects road speed at a given RPM.

Easy to compare multiple setups

Change tire diameter, gearing, or RPM and see the estimated road speed update immediately.

Works from common drivetrain formulas

Uses tire circumference, revolutions per mile, and overall gearing for a familiar quick-reference workflow.

Quick in the garage or on the road

Useful while comparing cruise RPM targets, tire sizes, and gear changes from your phone or desktop.

Editorial and accuracy note

Tire Speed Calculator combines a working converter with practical guidance on the same page. The page is designed to show the formula, examples, rounding notes, and related tools so visitors can judge whether the result fits a task such as shipping, recipes, logs, design, travel, or automotive planning.

Results are calculated in the browser with standard conversion factors for common units.
For official forms, engineering tolerances, medical decisions, or compliance work, verify the original measurement and the relevant source rule.
The surrounding notes focus on real use cases instead of repeating generic placeholder copy.

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Tire speed calculator FAQ

How does tire diameter affect vehicle speed at the same RPM?

A larger tire travels farther per wheel revolution, so vehicle speed increases at the same engine RPM when gearing stays the same.

What ratio should I enter in this calculator?

Use the overall gear ratio, which is the current transmission gear ratio multiplied by the final drive ratio.

Can I use this tire speed calculator on mobile?

Yes. The page works well on phones, tablets, and desktop screens.

Need another gearing or RPM calculator?

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