Motorcycle Tire Size Calculator
Compare motorcycle tire sizes side-by-side. See how a size change affects diameter, width, speedometer accuracy, and handling.
| Dimension | Current | New | Diff |
|---|---|---|---|
| Overall Diameter | 23.61" | 22.67" | -0.94" |
| Width | 4.72" | 4.72" | 0" |
| Sidewall Height | 3.31" | 2.83" | -0.48" |
| Circumference | 74.19" | 71.22" | -2.97" |
| Revs/Mile | 854 | 890 | +36 |
| Rim Diameter | 17" | 17" | 0" |
Common Motorcycle Tire Sizes
sport
cruiser
touring
adventure
How It Works
Enter two motorcycle tire sizes in metric format (e.g. 120/70ZR17). The calculator parses width, aspect ratio, and rim diameter, then computes all dimensions in inches.
Speed rating letters (Z, W, H, V) are automatically stripped during parsing so you can enter sizes exactly as printed on the tire sidewall.
The speedometer comparison shows how your actual speed differs from the dashboard reading when switching tire sizes. This is critical for motorcycle safety since even small differences are amplified at higher speeds.
How to Read a Tire Size
A tire size like P265/70R17 breaks down as:
- P — Passenger tire (LT = Light Truck)
- 265 — Section width in millimeters
- 70 — Aspect ratio (sidewall height is 70% of width)
- R — Radial construction
- 17 — Rim diameter in inches
Flotation sizes like 33x12.50R15 use inches: 33" overall diameter × 12.5" width on a 15" rim.
Frequently Asked Questions
How do motorcycle tire sizes work?
Motorcycle tire sizes use a metric format similar to car tires. For example, 120/70ZR17 means: 120mm width, 70 aspect ratio (sidewall is 70% of width), Z speed rating, R for radial, and 17-inch rim diameter. The speed rating letter (Z, W, H, V) indicates maximum safe speed.
Can I change my motorcycle tire size?
You can change sizes within a narrow range, typically staying within 10mm of the original width. Going too wide can cause clearance issues with the swingarm or chain. Going too narrow reduces grip. Always stay within the rim width range specified for the tire.
What does the Z in ZR mean on motorcycle tires?
Z is a speed rating indicating the tire is rated for sustained speeds above 149 mph (240 km/h). ZR means it is a Z-rated radial tire. Other common ratings: W (168 mph), V (149 mph), H (130 mph). Sport bikes typically use ZR-rated tires.
Does changing motorcycle tire size affect speedometer accuracy?
Yes. A larger tire increases the distance traveled per wheel revolution, so your speedometer will read lower than your actual speed. A smaller tire does the opposite. Use this calculator to see the exact speedometer difference between two sizes.