How To Read Metric Tire Size | Decode Sidewall Numbers

A code like P225/65R17 102H tells you tire width, sidewall ratio, build type, wheel diameter, load index, and speed symbol.

Reading a metric tire size feels messy the first time because the sidewall jams letters and numbers into one tight line. Once you know the order, the code stops looking random. You can tell what fits your wheel, how tall the sidewall is, and whether the tire matches your vehicle’s load and speed needs.

That matters when you’re shopping, checking a used car, or comparing one size against another. A tire can look close and still be wrong in a way that affects clearance, ride feel, gearing, or load capacity. The fix is simple: read the code from left to right and match it against the door-jamb placard or owner’s manual.

How To Read Metric Tire Size On A Sidewall

A common passenger-tire code looks like this: P225/65R17 102H. Each chunk tells one part of the story, and the order stays steady across most road tires.

Start With The Full Sequence

• P = tire type prefix, often passenger vehicle
• 225 = section width in millimeters
• 65 = aspect ratio, or sidewall height as a percent of width
• R = radial construction
• 17 = wheel diameter in inches
• 102 = load index
• H = speed symbol

Read it as one sentence in your head: passenger tire, 225 mm wide, sidewall height equal to 65% of that width, radial build, made for a 17-inch wheel, with load index 102 and speed symbol H. Once that pattern clicks, most sidewalls become easy to read.

What The Prefix Means

The first letter is easy to skip, but it gives context. P points to a passenger-car tire. LT means light truck. You may also see no prefix at all on some Euro-metric tires. In that case, the size still reads the same way, but the tire may be built to a different load standard than a P-metric version with the same numbers.

Width Comes First

The first number after the prefix is the tire’s section width in millimeters. In 225/65R17, the tire is 225 mm wide from sidewall to sidewall at its rated measuring width. It is not the tread width, which is why a 225 tire won’t always have a tread face that measures 225 mm across.

Aspect Ratio Is The Sidewall Height

The second number is the sidewall height as a percentage of the width. A 65-series tire has a sidewall height equal to 65% of 225 mm. Lower numbers mean a shorter sidewall. That usually brings a firmer ride and a sharper look. Higher numbers bring more cushion and a taller overall tire, assuming wheel size stays the same.

Construction And Wheel Diameter Finish The Size

The letter after the slash section is the build type. On modern passenger vehicles, R means radial. Then comes the wheel diameter in inches. A 17 in the code means the tire mounts on a 17-inch wheel. That number must match the wheel exactly. A 17-inch tire will not seat on a 16-inch or 18-inch wheel, no matter how close the rest of the size seems.

After the size itself, many tires add a service description. That’s the load index and speed symbol. These last marks don’t change fit, but they do affect what the tire is rated to carry and how it is approved to perform at speed.

Sidewall Mark	What It Means	Why It Matters
P	Passenger-tire prefix	Sets the tire category and load standard
LT	Light-truck prefix	Built for heavier-duty truck or van use
225	Section width in millimeters	Affects fitment, stance, and clearance
65	Aspect ratio	Changes sidewall height and overall tire height
R	Radial construction	Standard build on modern passenger vehicles
17	Wheel diameter in inches	Must match the wheel size exactly
102	Load index	Shows how much weight one tire can carry
H	Speed symbol	Shows the tire’s approved speed category

What Drivers Mix Up Most Often

The most common mistake is treating the sidewall’s max pressure marking as the pressure you should run every day. It isn’t. The right cold pressure for your vehicle comes from the Tire and Loading Information Label on the door jamb or from the owner’s manual. The tire sidewall can show a max load and max pressure that belong to the tire’s design limit, not your car’s day-to-day setting.

Another mix-up happens when two tires share the same size but not the same service description. A 225/65R17 tire with one load index may not replace another 225/65R17 tire if the vehicle asks for a higher rating. That’s one reason the full code matters, not just the first four marks.

A Sample Read Of 225/65R17 102H

Take the code chunk by chunk:

• 225: the tire is 225 mm wide
• 65: the sidewall height is 65% of 225 mm
• R: radial construction
• 17: made for a 17-inch wheel
• 102H: service description for load and speed

That means you can compare it with another size and spot what changed. If you move from 225/65R17 to 225/60R17, width stays the same, wheel size stays the same, but the sidewall gets shorter. If you move to 235/65R17, width grows, and that can change clearance and overall height.

Where To Find Extra Marks

Sidewalls often include more than the main size line. You may see M+S, 3PMSF, XL, DOT, a week-and-year date code, and UTQG grades. Those don’t replace the size code. They add detail about winter marking, reinforced load capacity, manufacturing data, and treadwear or traction grades. Michelin’s plain-English breakdown of tire sidewall markings lays out where those marks sit and what each one means.

How To Check A Replacement Size Without Guessing

If you’re buying replacements, don’t start with what “looks close.” Start with what the vehicle calls for. Then compare the sidewall code on your current tires against the door-jamb placard. If they match, you’ve got your baseline. If they don’t, trust the placard unless a tire shop has already fit an approved alternate size for your exact vehicle and trim.

Use this short check before you buy:

1. Read the tire code on the sidewall.
2. Read the size on the vehicle placard.
3. Match wheel diameter first.
4. Match width and aspect ratio next.
5. Check load index and speed symbol last.

That order prevents two costly slips: buying the wrong wheel diameter and ignoring the service description. Wheel diameter is a hard fit issue. Load and speed ratings are a safety and performance issue. Both need to line up with the vehicle’s spec.

Sample Size	What Changes	What You’ll Notice
225/65R17	Baseline sample	Balanced height and width for many crossovers
225/60R17	Shorter sidewall	Lower overall height and firmer feel
235/65R17	Wider tire	More width and possible clearance change
225/65R18	Larger wheel diameter	Needs an 18-inch wheel, not a 17-inch wheel
LT225/65R17	Truck-category prefix	Different load standard from P-metric
225/65R17 102H vs 102T	Speed symbol changes	Same fit, different speed category

Reading Load Index, Speed Symbol, And Date Code

Load index and speed symbol sit after the size, and drivers often skip them because the tire still “fits.” Fit is only half the job. A replacement tire should meet or exceed the vehicle maker’s required service description. A lower load or speed mark can leave the tire out of spec for the vehicle, even when the wheel diameter and size numbers match.

Load Index

The load index is a number such as 91, 98, or 102. Each number matches a set carrying capacity on a standard chart. You don’t need to memorize the full chart to read the tire. You just need to match what your vehicle asks for. If your placard calls for 102, don’t drop below 102 unless the vehicle maker lists another approved spec for that trim.

Speed Symbol

The speed symbol is a letter such as T, H, V, or W. It marks the tire’s speed category under test conditions. It is not a target speed. It is part of the tire’s design rating. If your vehicle came with V-rated tires, swapping to a lower category can change how the tire is approved to perform.

DOT Date Code

The DOT code helps you tell when the tire was made. The last four digits show week and year. A code ending in 4724 means the tire was built in the 47th week of 2024. That’s handy when you’re checking how old a tire is on a used car or on stock that has sat in storage.

Read The Code Once, Then Match The Vehicle Spec

If you strip the jargon away, a metric tire size says six things in a set order: type, width, sidewall ratio, construction, wheel diameter, and service description. That’s all. Read left to right, and the code becomes easy to repeat on any passenger tire you pick up.

The sidewall tells you what the tire is. The placard tells you what your vehicle wants. Put those two together and you can shop with a clear head, spot a mismatch in seconds, and avoid buying a tire that fits the wheel but not the car.