The motorcycle tire size meaning is printed right on the sidewall: in a size like 120/70ZR17, the first number is the tire's section width in millimeters, the second is the sidewall height as a percentage of that width, the letter shows the construction (R for radial, B for bias belted, or a dash for bias), and the last number is the rim diameter in inches. After the size you will usually find a load index and a speed rating letter, such as 58W. Read all of it before buying, because the wrong size or rating can affect handling and safety.
Below we break down every part of the code, cover the older inch and alpha sizes, and explain how to tell if a size will fit your bike.
Motorcycle tire size meaning, part by part
Take a common sport-bike front tire: 120/70ZR17 M/C (58W).
| Part | Example | What it means |
|---|---|---|
| Section width | 120 | Nominal width of the tire in millimeters |
| Aspect ratio | 70 | Sidewall height is 70% of the width (about 84 mm here) |
| Speed category letter | Z | Older marking for tires rated above 240 km/h (149 mph) |
| Construction | R | Radial construction |
| Rim diameter | 17 | Fits a 17-inch wheel |
| Motorcycle marking | M/C | Made for motorcycle use only |
| Load index | 58 | A number you look up in a load table to find the maximum load |
| Speed rating | W | Rated for up to 270 km/h (168 mph) |
A rear example: 180/55ZR17 M/C (73W) is 180 mm wide with a sidewall 55% of that width, for a 17-inch rim.
Section width
The first number is the tire's nominal width in millimeters, measured on the specified rim. Actual width varies a bit by brand and by how wide your rim is. A wider rim spreads the tire; a narrower rim pinches it into a rounder profile.
Aspect ratio
The number after the slash is the height of the sidewall as a percentage of the width. A 120/70 tire has a sidewall about 84 mm tall. A 120/60 tire of the same width has a shorter sidewall, which lowers the bike slightly and changes how it turns in.
If no aspect ratio is shown, older conventions assume a taller sidewall, so check the maker's chart.
Construction letter
- R: radial. The cords run at 90 degrees to the direction of travel.
- B: bias belted. Diagonal cords with a belt under the tread. Common on cruisers and touring bikes, such as 150/70 B 17.
- – (dash): bias ply, with diagonal cords and no belt.
Never mix radial and bias construction front and rear unless the tire and bike maker approve it. Our guide to tube vs tubeless motorcycle tires covers the other construction choice you will see on the sidewall.
Rim diameter
The final number is the wheel diameter in inches. It must match your wheel exactly. A 17-inch tire will not fit a 16-inch or 18-inch rim.
Load index and speed rating
After the size you usually see a group like (58W) or 69H.
- Load index: a two- or three-digit number that cross-references a load table. The number itself is not pounds. Higher numbers mean the tire can carry more weight at the specified pressure.
- Speed rating: a letter that shows the maximum sustained speed the tire is built for under its rated load. Common motorcycle ratings include H (130 mph), V (149 mph) and W (168 mph).
When a Z appears inside the size, such as 120/70ZR17, the tire is rated for speeds above 149 mph. The exact limit is shown by the letter after the load index. A W in brackets, such as (W), means the tire is rated above 168 mph, with the actual top speed set by the tire maker.
Always use a load index and speed rating at least as high as your owner's manual specifies. Our guide to motorcycle tire load index and speed rating has the full tables.
Other sizing systems you might see
Older and vintage bikes, and some dirt bikes and cruisers, still use other formats.
Inch sizes
A tire marked 4.00-18 or 3.25-19 is sized in inches. The first number is the approximate width in inches and the second is the rim diameter. The dash means bias construction. These usually have a high profile.
Alpha sizes
Some cruiser and touring tires use letters, such as MT90-16 or MU85B16. The letters stand for a width class and the number after them is the aspect ratio. Alpha sizes do not translate exactly into metric, so use the tire maker's conversion chart.
| System | Example | Common on |
|---|---|---|
| Metric | 130/90-16 | Most modern bikes |
| Metric radial | 190/50ZR17 | Sport and naked bikes |
| Inch | 3.00-21 | Dirt bikes, vintage bikes |
| Alpha | MT90B16 | Older cruisers and tourers |
Other sidewall markings worth knowing
- TL or Tubeless: can be run without a tube on a suitable rim.
- TT or Tube Type: needs an inner tube.
- Front / Rear: many motorcycle tires are designed for one position only.
- Rotation arrow: shows which way the tire must spin.
- DOT code: the last four digits show the week and year of manufacture, so 0121 means the first week of 2021. See how to read a motorcycle tire date code.
- Max load and max pressure: the maximum, not the recommended pressure. Use the pressure on your bike's label or manual.
Can you change your motorcycle tire size?
Small changes are possible, but there are trade-offs.
Going wider on the rear:
- Can slow steering because the profile changes
- May rub the chain, swingarm, belt or fender
- May not suit your rim width
Changing the aspect ratio:
- Changes ride height and the bike's geometry
- Throws off the speedometer slightly
- Can change how quickly the bike turns in
Safe approach:
- Start with the sizes listed in your owner's manual.
- Check the tire maker's fitment guide for your exact model and rim width.
- Keep front and rear tires from the same maker and model line where possible.
- If in doubt, ask a tire shop before buying.
For a broader look at choosing a tire, see how to choose motorcycle tires.
How to find the right size for your bike
- Look at your current tires. But confirm they are correct, since a previous owner may have fitted the wrong size.
- Check the owner's manual. It lists stock sizes, load index, speed rating and pressure.
- Check the label on the bike. Many bikes have a tire and pressure label on the swingarm or frame.
- Use the tire maker's fitment search. It filters by year, make and model.
Cost of new motorcycle tires
Costs vary by bike, region and shop. Size affects price: a wide 17-inch sport radial usually costs more than a narrow bias tire. Mounting and balancing are often extra, and many shops charge less if you bring the wheels in off the bike. See our guide to motorcycle tire replacement cost for typical ranges.
When to see a mechanic
Tires are your only contact with the road. Have a professional check your bike if:
- You are not sure the tire size on the bike matches the manual
- A new tire rubs anything, or the bike handles strangely after a change
- You see bulges, cuts, cracks or cords showing
- The bike wobbles or weaves after a tire change
- You want to change size and are not sure it is safe
A motorcycle tire shop can confirm fitment, mount and balance tires and check your wheels.
Frequently asked questions
What does 120/70ZR17 mean on a motorcycle tire?
The tire is about 120 mm wide, the sidewall height is 70% of that width, the Z and R mean it is a high-speed radial, and it fits a 17-inch rim.
Can I put a wider tire on my motorcycle?
Sometimes, but a wider tire changes the profile and handling and may rub the swingarm, chain or fender. Stick to sizes your manual or the tire maker lists for your rim width.
What does M/C mean on a tire?
M/C means the tire is made for motorcycle use. Do not fit a car or trailer tire to a motorcycle.
Do front and rear motorcycle tires have to be the same brand?
It is best to use a matched front and rear pair from the same maker and model line. Don't mix radial and bias construction front and rear unless your bike and tire maker approve that combination.
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References
- Tire code (Wikipedia) (en.wikipedia.org)