Tire guide
How to read a motorcycle tire size
Every motorcycle tire has its size printed on the sidewall. Here's how to read it, how the metric, letter and inch systems compare, and which sizes fit which bikes.
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Reading a metric size
Most dirt bike, dual sport and street tires use the metric system. Take 110/90-19 62M, a common rear MX size:
- 110: width
- The section width in millimeters, sidewall to sidewall.
- 90: aspect ratio
- Sidewall height as a percentage of the width. 90% of 110 mm is a 99 mm sidewall. A lower number means a shorter sidewall.
- - / R / B: construction
- A dash means bias-ply, which almost every off-road tire is. R is radial and B is bias-belted. ZR marks a radial for speeds over 149 mph.
- 19: rim diameter
- The wheel size in inches. This number has to match your rim exactly.
- 62M: load and speed
- The maximum load and speed the tire is rated for. See the tables below.
Same rim, different shape: 80/100-21 and 90/90-21 both fit a 21" front wheel. The 90/90 is 10 mm wider with almost the same sidewall height (81 mm vs 80 mm), which is why it's popular on ADV and enduro bikes.
Load, speed and other markings
| Index | Max load per tire |
|---|---|
| 51 | 430 lb (195 kg) |
| 57 | 507 lb (230 kg) |
| 62 | 584 lb (265 kg) |
| 63 | 600 lb (272 kg) |
| 69 | 716 lb (325 kg) |
| 73 | 805 lb (365 kg) |
| Letter | Max speed |
|---|---|
| J | 62 mph |
| L | 75 mph |
| M | 81 mph |
| P | 93 mph |
| Q | 99 mph |
| R | 106 mph |
| S | 112 mph |
| T | 118 mph |
| H | 130 mph |
| V | 149 mph |
| W | 168 mph |
- TT / TL
- Tube type or tubeless. Most dirt bike rims are spoked and need a tube. A tubeless tire can run with a tube, but a tube-type tire shouldn't run without one.
- Front / Rear and the arrow
- Many tires are made for one position only. Mount them so the arrow points in the direction the wheel turns going forward.
- DOT and NHS
- DOT means the tire is approved for US roads, which matters for a street-legal dual sport. NHS means "not for highway service": competition only.
- Date code
- The last four digits after "DOT" are the week and year it was made. 2425 means week 24 of 2025.
Letter (alpha) sizes
Older bikes and many cruisers use letter sizes such as MT90-16. The "M" means motorcycle, the second letter stands for a width, the number is the aspect ratio and the last number is the rim. These are the closest metric sizes:
| Letter size | Closest metric | Typical use |
|---|---|---|
| MH90 | 80/90 | Front, small and vintage bikes |
| MJ90 | 90/90 | Front |
| MM90 | 100/90 | Front, cruiser and touring |
| MN90 | 110/90 | Front |
| MP85 | 120/80 | Rear, light bikes |
| MR90 | 120/90 | Front or rear |
| MT90 | 130/90 | Front or rear, cruiser |
| MU90 / MU85 | 140/90 / 140/80 | Rear, cruiser |
| MV85 | 150/80 | Rear, cruiser and touring |
Our tire finder converts letter sizes for you: search MT90-16 and it shows 130/90-16 tires too.
Inch sizes
Trials, vintage and some enduro tires use inches, like 4.00-18: about 4 inches wide on an 18" rim. Inch sizes don't state a sidewall height, so treat the metric matches as close, not exact.
| Inch width | About | Closest metric |
|---|---|---|
| 2.75 | 70 mm | 70/100 |
| 3.00 | 76 mm | 80/100 |
| 3.50 | 89 mm | 90/90 |
| 4.00 | 102 mm | 100/100 |
| 4.10 | 104 mm | 110/100 |
| 4.50 | 114 mm | 120/90 |
| 5.10 | 130 mm | 130/90 |
ATV and flotation sizes
ATV, UTV and some fat tires are sized by overall dimensions in inches. 25x8-12 means 25" tall, 8" wide, on a 12" rim. Front and rear are often different, like 25x8-12 front and 25x10-12 rear.
Common sizes by bike
Starting points only. Always check your owner's manual or the tire on your bike now. Tap a size to see every tire we carry in it.
Pick tread for your dirt
Size gets the tire on the rim. Tread decides how it hooks up. Our riders race and ride everything from Central Oregon trails to rock gardens and deep MX ruts:
Central Oregon trail
Dust, pumice and lava rock change by the mile. An intermediate tread with a medium-hard compound is the safe all-rounder here.
Shop intermediate tires →Rock and hard enduro
Slow, technical climbs reward a soft, sticky compound that wraps around rock. Many hard enduro riders also run lower pressure, with a mousse or a heavy-duty tube.
Shop enduro tires →Prepped MX track
Loamy, watered tracks and deep ruts want a soft-to-intermediate MX tire with tall, widely spaced knobs that clean out.
Shop soft terrain tires →Can I change size?
- Keep the rim size. A 19" tire only fits a 19" wheel.
- One step wider is usually fine on the rear, such as 110/90-19 to 120/90-19, but check chain, swingarm and fender clearance with the wheel spun by hand.
- Go easy on the front. Front width and height change how the bike steers and turns in.
- Match or beat the load and speed rating on your bike's placard or in the manual, especially on a street-legal bike.
- Don't mix radial and bias on a street bike unless the bike or tire maker approves the pairing.
FAQ
What does 110/90-19 mean on a tire?
It's a tire 110 mm wide with a sidewall 90% as tall as it is wide (99 mm), built bias-ply (the dash) to fit a 19-inch rim.
Is 80/100-21 the same as 90/90-21?
No. Both fit a 21-inch front wheel and stand about the same height, but the 90/90-21 is 10 mm wider. It's common on ADV and enduro bikes; 80/100-21 is the standard MX front.
What does the M in 62M mean?
It's the speed rating: M is rated to 81 mph. The 62 is the load index, rated to 584 lb per tire.
How do I tell how old my tire is?
Find the DOT code on the sidewall. The last four digits are the week and year it was made, so 2425 means week 24 of 2025.
Can I put a tubeless tire on a tube-type rim?
Yes, with a tube inside. You can't run a tube-type tire without a tube, and most spoked dirt bike rims aren't sealed for tubeless use.
Can I put a wider tire on my dirt bike?
Usually one size wider on the rear is fine if it clears the chain, swingarm and fender. Keep the same rim diameter and don't go below your bike's load and speed rating.