How To Read A Motorcycle Tire | Sidewall Codes Decoded

A motorcycle tire sidewall tells you the size, load index, speed rating, type, and build date in one compact code.

A motorcycle tire is a label wrapped around rubber. Once you know where each number and letter sits, you can tell whether a tire fits your bike, carries the right weight, matches the bike’s speed range, and was built recently enough to buy with confidence.

That matters on a new set, a used-bike inspection, or a late-night parts search when five similar sizes all seem right. They aren’t. A single letter can change the construction. A small drop in load index can rule a tire out. And an old date code can turn a “deal” into dead money.

How To Read A Motorcycle Tire On The Sidewall

Most modern street tires follow the same reading order. Start at the big size code, then move to the service description, then scan the extra marks around the sidewall.

1. Read the size first. This tells you width, sidewall profile, and rim diameter.
2. Find the service description. This is the load index and speed symbol.
3. Check construction and type. You may see R, ZR, B, TL, or TT.
4. Find fitment clues. Front, Rear, Rotation, and M/C matter.
5. Finish with the date code. That tells you when the tire was made.

Say the sidewall reads 180/55 ZR17 M/C (73W) TL. You can break it down like this:

• 180 = tire width in millimeters
• 55 = sidewall height as 55% of the width
• ZR = radial tire in a high-speed category
• 17 = rim diameter in inches
• M/C = motorcycle tire
• 73 = load index
• W = speed symbol
• TL = tubeless

What The size numbers mean

The first number is the tire’s width at its widest point, measured in millimeters. The second number is the aspect ratio. That’s the sidewall height as a percentage of the width, not a height in millimeters by itself. The last number is the wheel size the tire fits, measured in inches.

So a 120/70-17 tire is 120 mm wide, with a sidewall height equal to 70% of that width, and it fits a 17-inch rim. If you swap that to a 120/60-17, the rim size stays the same, but the sidewall gets shorter and the tire profile changes. That can alter steering feel, ride height, and clearance.

What The letters after the size mean

After the size, you’ll often see the tire’s service description. That is the load index and speed symbol. On many tires, the load index is a two-digit number and the speed symbol is one letter, such as 58W or 73H.

The load index is not the weight in pounds or kilograms printed out in full. It is a code that matches a load chart. The speed symbol is a letter code for the tire’s tested speed range. If you want a factory chart for those values, Bridgestone’s MC tire designations chart lists motorcycle load index and speed symbol values in one place.

Marking	What It Means	What You Should Check
120	Tire width in millimeters	Match the bike’s listed size
70	Sidewall height as a percentage of width	Watch ride height and handling changes
17	Rim diameter in inches	Must match the wheel exactly
R or ZR	Radial construction	Use the construction type listed for your bike
B or a dash	Bias-belted or bias-ply style marking	Do not swap by guesswork
M/C	Motorcycle tire marking	Confirms motorcycle fitment
58W / 73H	Load index plus speed symbol	Meet or exceed the bike maker’s minimum spec
TL	Tubeless tire	Pair with the right rim type
TT	Tube-type tire	Use a tube where the fitment calls for one
Front / Rear	Position-specific tire	Do not flip front and rear use
Rotation	Direction-of-rotation arrow	Mount the tire the right way round
DOT + 4 digits	Week and year of manufacture	Check age before you buy

Reading Motorcycle Tire Codes On Older And Newer Bikes

Not every motorcycle tire uses the same style of sizing. Modern sport and street bikes usually use metric sizing, such as 120/70ZR17. Cruisers, vintage bikes, and some smaller machines may use inch sizing or older alpha-numeric sizing, such as 4.00-18 or MT90B16.

That is where riders get tripped up. A tire can look close on screen and still be wrong in load, width, or profile. If your bike came with alpha-numeric or inch sizes, cross-reference the owner’s manual or the tire maker’s fitment data before you buy. Do not swap to a near match just because the wheel diameter is the same.

Marks That Tell You More Than Size

The sidewall also carries clues that shape fit and use:

• TL or TT tells you whether the tire is tubeless or tube-type.
• Front or Rear marks show position-specific fitment.
• Rotation arrows show the mounting direction.
• TWI points to tread wear indicator bars in the grooves.
• Max load and max cold pressure may be printed in text on the sidewall.

Those marks are not decoration. Mounting a directional tire backward, fitting a rear where a front belongs, or mixing tube-type and tubeless parts the wrong way can spoil handling and shorten tire life.

Date Code And Wear Clues You Should Not Miss

The DOT code is one of the first things to read on any new-old-stock tire or used bike. The last four digits show the week and year of manufacture. A code ending in 1424 means the tire was built in the 14th week of 2024. NHTSA’s Tire Identification Number interpretation spells out that format and how the week is counted.

You may need to check both sides of the tire. On many tires, the full date code appears on only one sidewall. If the four-digit block is missing, roll the bike or inspect the opposite side.

Then scan the tread and sidewall. Uneven wear on one shoulder, flat-centre wear, cracks near the bead, cuts, plugs, and cupping all tell a story. Some of those signs point to age. Others point to pressure problems, suspension issues, or lots of straight-line miles.

What You See	What It Often Means	Safer Move
Load index lower than stock	The tire may not carry the bike and rider load properly	Choose a tire that meets or tops the listed minimum
Speed symbol lower than stock	The tire is not rated for the bike’s required range	Stay at the listed rating or above
Old DOT date	The tire may have aged on the shelf	Ask for a newer tire before buying
Rear tire fitted to the front	Carcass and tread design may not suit front-wheel duty	Use the marked position only
Wrong rotation direction	Wet grip and wear can suffer	Remount using the arrow direction
Tube-type and tubeless parts mixed by guesswork	Air retention and fit can go wrong	Match tire, tube, and rim type to the spec sheet

Match The Tire To The Bike, Not The Wheel Alone

Many riders stop at width and rim size. That is only half the job. The right tire has to fit the motorcycle’s intended use, weight, and chassis setup too.

Before you order, check these points:

• Use the owner’s manual or the bike maker’s fitment label as the first reference.
• Match the full size code, not just the last number.
• Meet or top the listed load index and speed symbol.
• Use the marked front or rear position.
• Confirm tube-type or tubeless fitment.
• Leave enough room for chain, fender, swingarm, and mudguard clearance.

If you want a different profile or brand, compare the spec sheet before you buy. Two tires with the same printed size can still run wider, taller, or rounder than you expect. That can change turn-in feel and clearance.

Reading A Real Sidewall In One Pass

Say you’re staring at this code: 120/70 ZR17 M/C (58W) TL Front.

• 120/70 tells you the width and profile.
• ZR17 tells you the construction family and 17-inch rim size.
• M/C confirms it is a motorcycle tire.
• 58W tells you the coded load and speed range.
• TL says it is tubeless.
• Front says it belongs on the front wheel.

Once you can read that line cleanly, tire shopping gets easier. You stop guessing from tread photos alone. You stop buying a tire just because the diameter looks right. And you start checking the marks that decide fit, age, and safe use before money changes hands.