Formula Used
Wheel RPM from linear speed:
Wheel RPM = (speed in meters per second ÷ circumference in meters) × 60
Wheel circumference:
Circumference = π × effective diameter
Engine RPM:
Engine RPM = wheel RPM × gear ratio × final drive × transfer case × overdrive ÷ efficiency
Required diameter:
Diameter = (speed × 60 ÷ wheel RPM) ÷ π
Imperial shortcut: wheel RPM is approximately speed in MPH multiplied by 336, then divided by tire diameter in inches.
How to Use This Calculator
- Select whether you need wheel RPM, speed, required diameter, or engine RPM.
- Enter speed and select its unit.
- Choose direct diameter, circumference, tire notation, or loaded radius.
- Add tire wear, growth, deflection, slip, or speed correction when needed.
- Enter selected gear, final-drive, transfer-case, and overdrive ratios.
- Set efficiency, redline, and maximum wheel RPM limits.
- Add speed and diameter values for side-by-side comparison.
- Calculate, copy results, export CSV, or print a PDF.
Worked Example
A vehicle travels at 60 mph using a 26.7-inch tire. The tire circumference is approximately 2.13 meters. The wheel rotates near 754 RPM before tire corrections. With a 3.73 final drive, engine speed depends on the selected transmission gear.
| Input | Example value |
|---|---|
| Speed | 60 mph |
| Tire diameter | 26.7 inches |
| Selected gear | 1.00 |
| Final drive | 3.73 |
| Efficiency | 100% |
Frequently Asked Questions
What determines wheel RPM?
Wheel RPM depends mainly on road speed and effective rolling circumference.
Why is loaded radius different from tire radius?
Vehicle weight compresses the tire, reducing its effective rolling radius.
Does tire slip increase wheel RPM?
Yes. Positive slip means the wheel rotates faster than road speed suggests.
How does a larger tire affect RPM?
A larger tire travels farther per revolution, reducing wheel RPM at equal speed.
How is engine RPM calculated?
Wheel RPM is multiplied by the combined transmission and final-drive ratios.
Why include drivetrain efficiency?
Efficiency provides an optional practical adjustment for losses and converter behavior.
Can I enter a tire size like 205/55R16?
Yes. The calculator derives sidewall height and overall unloaded diameter automatically.
What is tire growth?
Some tires expand slightly at high speed, increasing effective circumference.
Can this calculate speedometer error?
Yes. The result compares entered speed with the calculated rolling speed.
Is the MPH shortcut exact?
No. The 336 constant is rounded and assumes diameter in inches.
Can I use this for bicycles or machinery?
Yes. Use suitable dimensions, ratios, and realistic correction values.
Accuracy Notice
Real tire circumference changes with pressure, load, temperature, tread wear, deformation, and manufacturing tolerance. Verify critical speed or drivetrain decisions using measured rolling circumference and manufacturer data.