Compare Motorcycle Tire Sizes
Use this tool to compare your current tire size with a new size and estimate diameter change, circumference change, revs per mile, and speedometer error.
Current Tire
New Tire
Why a motorcycle tire size calculator matters
Changing tire size can alter much more than appearance. A different tire profile can affect handling feel, acceleration, braking behavior, speedometer accuracy, ABS calibration sensitivity, and even chain/swingarm clearance. A quick size comparison before buying helps you avoid expensive mistakes.
Most riders consider a size change for one of three reasons: better grip availability, improved turn-in feel, or cost and availability. Whatever your reason, understanding the numbers first is the safest path.
How to read motorcycle tire sizes
Example: 120/70-17
- 120 = tire width in millimeters.
- 70 = aspect ratio (sidewall height as a percentage of width).
- 17 = wheel/rim diameter in inches.
So for a 120/70-17 tire, sidewall height is 120 × 0.70 = 84 mm. Total tire diameter is rim diameter (17 in × 25.4) plus two sidewalls.
What this calculator shows you
- Sidewall height for each size.
- Overall tire diameter in mm and inches.
- Circumference and rolling distance per revolution.
- Revolutions per mile estimate.
- Speedometer difference at your chosen indicated speed.
- Ride height change from radius difference.
Formulas used
This calculator uses standard geometry:
- Sidewall height (mm) = width × (aspect ratio / 100)
- Overall diameter (mm) = rim(in) × 25.4 + 2 × sidewall height
- Circumference (mm) = π × overall diameter
- Revs per mile = 63,360 in / circumference(in)
- Actual speed = indicated speed × (new circumference / current circumference)
Real-world tire dimensions can vary slightly by brand and model, so treat results as a planning estimate.
How much size change is usually acceptable?
Many riders try to keep overall diameter change within about ±2%. That helps preserve factory geometry and electronics behavior. Small changes can still be noticeable, especially on sport bikes.
General effects of size changes
- Larger diameter: lower engine RPM at speed, slightly taller gearing, potentially slower turn-in.
- Smaller diameter: higher RPM at speed, shorter gearing, usually quicker turn-in.
- Wider tire: may improve rear grip feel, but can reduce agility and require proper rim width.
Safety and fitment checklist before switching sizes
- Confirm the new size is approved for your wheel width.
- Check chain guard, swingarm, fender, and fork clearance.
- Verify load index and speed rating meet or exceed OEM specs.
- If your bike has ABS/traction control, avoid large front/rear diameter mismatches.
- Re-check pressure recommendations for the new tire model.
Example comparison
If you switch from a 120/70-17 front tire to a 130/70-17, you increase sidewall height and overall diameter. The bike may read a little lower speed than actual (depending on where speed is measured), and steering may feel slightly slower. The exact effect appears in the calculator output above.
Frequently asked questions
Can I just go one size wider?
Sometimes yes, but only if the rim width supports it and you still have safe clearance. Wider is not automatically better.
Will this affect my speedometer?
Yes, circumference changes affect indicated versus actual speed. Even small percentage changes can be noticeable on long rides.
Does tire brand matter if the size is the same?
Absolutely. Different carcass profiles can produce different real dimensions and handling feel even with identical size markings.
Final note
Use this motorcycle tire size calculator as a fast planning tool, then verify fitment with your manufacturer specs and tire maker data sheet. A few minutes of checking now can save money and improve both safety and confidence on the road.