Motorcycle Tire Sizes: Metric, Inch and Alphanumeric Codes Explained

How to read a metric motorcycle tire size

Metric sizing is used on almost every road bike built since the 1990s. Taking the common sport-bike rear tire 180/55ZR17 M/C (73W) TL:

Load indexes and speed letters use the same tables as car tires (see the tire size guide), but motorcycle values are much lower: typical road fronts are 54-58 (212-236 kg) and rears 69-75 (325-387 kg).

Inch and alphanumeric sizes

Older bikes, dirt bikes and many cruisers still use the two older systems.

Inch sizing (3.00-21, 4.10-18)

The first number is the approximate section width in inches and the second is the rim diameter. A 3.00-21 is about 3 in (76 mm) wide on a 21-inch rim. The aspect ratio is not stated; it is close to 100%, which is why 3.00-21 and 80/100-21 are treated as near equivalents.

Alphanumeric sizing (MT90B16, MH90-21)

Used mainly on American cruisers. The code reads: M (motorcycle), a width letter, the aspect ratio, construction (B = bias-belted, dash = bias) and rim size. The width letters run alphabetically from narrow (MH) to wide (MV). The most frequently cross-referenced pair is MT90B16 and 130/90B16, which tire makers list as equivalents. Because the width letters cover a band rather than an exact size, use the maker's cross-reference chart before swapping systems.

Motorcycle tire sizes by bike type

These are the size pairs most often fitted from the factory in each class. Your bike's exact sizes are in the owner's manual and on the tire placard on the swingarm or frame.

Calculated diameters of common sizes

Motorcycle tires have rounded profiles, so real diameters vary more between brands than car tires do. As a reference:

The 190/50 and 190/55 comparison is a common question: the /55 is 19 mm taller, which raises the rear about 10 mm and quickens the steering slightly. Riders and manufacturers use this to fine-tune geometry, so stick with the size your bike's chassis was set up for unless you are adjusting it deliberately.

Rim width for each tire width

Motorcycle rims are stamped with a size such as MT5.50x17: 5.50 in wide, 17 in diameter. Each tire width has a measuring rim and an approved range.

A tire on a rim narrower than intended has a peaked profile and a smaller contact patch at lean. On a wider rim it is flattened and turns in slowly. Each tire maker publishes its own approved range per size.

Choosing replacement motorcycle tires

1. Match the sizes on the bike's placard, including the rim diameter and, for radials, the aspect ratio.
2. Match or exceed the load index and speed symbol. A ZR tire satisfies a W or V requirement only if it carries that letter or higher in its service description.
3. Buy as a pair from one range. Fronts and rears are designed together; mixing a sport front with a touring rear changes the handling balance.
4. Respect construction. Do not combine a radial front with a bias rear unless the bike or tire maker approves it. Bias front with radial rear is sometimes approved, never the other way round.
5. Fit by the arrows. Mount each tire in its marked position with the rotation arrow in the riding direction.

Dirt bike and youth sizes

Off-road bikes use inch or metric sizes on 10-21 inch rims:

• Pit bikes and small youth bikes (50-110 cc): 2.50-10 to 2.50-14 front, 2.75-10 to 3.00-12 rear.
• Youth 85 cc: 70/100-17 front and 90/100-14 rear (small wheel) or 70/100-19 and 90/100-16 (big wheel).
• Full-size motocross and enduro: 21-inch front, 18- or 19-inch rear, as in the table above.

For quads and side-by-sides, which use a completely different size format, see the ATV tire size guide. Bicycle tires, including e-bike and motorbike-style fat tires, are in the bicycle tire guide, and rim and hub fitment is covered in the wheel size guide.

Frequently asked questions