Motorcycle Tire Size Calculator
Read a motorcycle tire code. Use the calculator below. Results update as you type.
How the Motorcycle Tire Size Calculator Works
This calculator works by decoding a metric motorcycle marking such as 180/55ZR17 into width, sidewall, rim and overall diameter. Motorcycle sizes use the same metric logic as car sizes.
- Enter the size, for example 180/55ZR17.
- Read the width: 180 mm (7.09 in).
- Read the sidewall: 99 mm (3.90 in).
- Read the diameter: 24.80 in (630 mm).
The Formula
The formula is Overall Diameter = (Rim × 25.4) + 2 × (Width × Aspect Ratio ÷ 100).
Sidewall (mm) = Width × Aspect Ratio ÷ 100 D (mm) = (Rim × 25.4) + 2 × Sidewall Circumference (mm) = π × DWorked example for 90/90R21: the sidewall is 81 mm, the rim is 533.4 mm, and the diameter is 695.4 mm (27.38 in).
A Z in the size (ZR) marks a tire rated above 240 km/h (149 mph). A dash in place of R marks bias-ply construction.
Conversion Table
The conversion table lists nominal dimensions for 10 motorcycle sizes. Sizes run from adventure fronts (90/90R21) to cruiser rears (240/40R18).
Sport bikes use 17 in rims front and rear. Adventure bikes pair a 19 in or 21 in front with a 17 in or 18 in rear.
| Size | Typical Position | Diameter (in) | Diameter (mm) | Sidewall (mm) |
|---|---|---|---|---|
| 90/90R21 | Front (adventure) | 27.38 | 695 | 81 |
| 110/80R19 | Front (adventure) | 25.93 | 659 | 88 |
| 120/70ZR17 | Front (sport) | 23.61 | 600 | 84 |
| 130/90R16 | Front (cruiser) | 25.21 | 640 | 117 |
| 150/70R17 | Rear (adventure) | 25.27 | 642 | 105 |
| 160/60ZR17 | Rear (sport) | 24.56 | 624 | 96 |
| 180/55ZR17 | Rear (sport) | 24.80 | 630 | 99 |
| 190/50ZR17 | Rear (sport) | 24.48 | 622 | 95 |
| 200/55ZR17 | Rear (hyper) | 25.66 | 652 | 110 |
| 240/40R18 | Rear (cruiser) | 25.56 | 649 | 96 |
What Is the Motorcycle Tire Size Calculator?
The Motorcycle Tire Size Calculator is a tool that decodes motorcycle-specific tire markings into dimensions. Motorcycle tires have rounded profiles, so the bike leans onto the shoulder of the tread in corners.
Diameter changes on a motorcycle shift ride height, steering geometry and speedometer readings at the same time. A taller rear tire raises the rear and quickens steering.
Common Uses
This calculator has 4 uses: replacements, rear-width upgrades, geometry checks and speedometer checks.
- Replace tires: Decode the size on the old tire.
- Upgrade rear width: Compare a 180 and a 190 rear.
- Check geometry: See ride height change from a taller tire.
- Check speedometers: Find the error after a size change.