Motorcycle tire sizes look confusing at first. One tire says 90/90-18, another says 3.00-18, and a third says 110/80-17. What do all these numbers mean?
This guide explains both sizing systems, shows you how to read them, and gives you practical rules to avoid buying the wrong tire.
Two common formats
Motorcycle tires use two sizing systems:
- Metric:
90/90-18= width 90mm / aspect 90% / rim 18” - Inch:
3.00-18= approximate width 3.00” / rim 18”
Inch sizes and metric sizes are different marking systems. A tire maker's conversion chart can list approximate equivalents, but a listed match is not the same as an identical size. Check with the motorcycle or tire maker before substituting one for the other.
Metric Format Explained
The metric format has three parts: width / aspect ratio - rim diameter.
| Number | Meaning | Example (90/90-18) |
|---|---|---|
| 90 (first) | Tire width in millimeters | 90 mm wide |
| 90 (second) | Aspect ratio (sidewall height ÷ width) | Sidewall = 81mm |
| 18 | Rim diameter in inches | Fits 18” rim |
Pro tip: To calculate sidewall height, multiply width × aspect ratio ÷ 100. For 90/90-18: 90 × 0.90 = 81mm sidewall.
Inch Format Explained
The inch format is simpler but less precise:
| Number | Meaning | Example (3.00-18) |
|---|---|---|
| 3.00 | Tire width in inches | ≈ 76mm wide |
| 18 | Rim diameter in inches | Fits 18” rim |
Unlike a metric size, an inch size does not state an aspect ratio. You cannot calculate the sidewall height from the size alone; use the tire maker's published dimensions for the specific model.
Quick Rules That Prevent Mistakes
- Keep rim diameter the same — a 18” tire won’t fit a 17” rim, period.
- Check rim width range — wider tires may not fit narrow rims safely.
- Verify clearance — wider tires need room in the swingarm and fairings.
- Load & speed ratings — matter for highway speeds and loaded touring.
- Match front/rear proportions — don’t put an extreme size change on both ends.
Common Motorcycle Tire Sizes
Here are some of the most common motorcycle tire sizes you’ll encounter:
| Size | Common On | Type |
|---|---|---|
| 90/90-18 | Dual-sport, commuter 125cc | Metric |
| 3.00-18 | Classic, dual-sport | Inch |
| 110/80-17 | Standard street bikes | Metric |
| 130/70-17 | Rear tire, standard bikes | Metric |
| 150/70-17 | Larger cruisers, sport bikes | Metric |
| 2.75-18 | Small commuters, scooters | Inch |
| 90/100-19 | Off-road, dirt bikes | Metric |
Tube-Type (TT) vs Tubeless (TL)
Every tire is marked as either TT (Tube Type) or TL (Tubeless):
- TT (Tube-Type): Requires an inner tube. Common on dual-sport and classic bikes with spoked wheels.
- TL (Tubeless): Seals directly to the rim. No tube needed. Standard on modern street bikes with cast alloy wheels.
📋 Before You Buy — Quick Checklist
- Check your current tire's size (written on the sidewall)
- Confirm TT or TL for your wheel type
- Verify rim diameter matches exactly
- Check load index for your bike weight
- Consider riding conditions (street, off-road, mixed)
How to Choose the Right Tire
Selecting the right motorcycle tire depends on several factors:
- Riding style: Commuter, touring, off-road, sport
- Bike weight: Heavier bikes need higher load ratings
- Typical speed: Highway riders need higher speed ratings
- Road conditions: Wet, dry, mixed surfaces
- Budget: Premium vs. budget brands offer different longevity
When shopping for motorcycle tires online, always double-check the size format and make sure the tire matches your bike’s specifications. When in doubt, consult your owner’s manual or a professional tire dealer.
Once you've got the size right, run through our checklist for choosing motorcycle tires before you order.