A tire number tells you width, sidewall height, construction, wheel size, load limit, and speed rating printed on the sidewall.
Tire sidewall numbers look messy at first glance. Once you know the order, they read like a short sentence. That one string tells you what wheel the tire fits, how tall the sidewall is, how much weight it can carry, and the speed class it was built for.
That matters when you’re replacing one worn tire, checking a used car, or comparing deals online. Read the number the right way and you dodge a bad fit, a weak load rating, or a tire that changes how the car rides and brakes.
How To Read Tire Number On Any Passenger Car
Start with a common size such as P225/65R17 102H. Read it from left to right. Each letter or number has one job. Don’t skip around the sidewall yet. Lock onto the main size string first, then read the extra marks after that.
Start With The Service Type
The first letter, if there is one, points to the tire’s class. P means passenger vehicle. You may also see no letter at all, which often means a Euro-metric passenger tire. On trucks, trailers, and spares, that prefix changes, and so does the tire’s intended use.
Read The Size Block Left To Right
Using P225/65R17 as the sample:
- 225 is the tire width in millimeters, measured across the sidewall.
- 65 is the aspect ratio. The sidewall height is 65% of the width.
- R means radial construction, which is what most modern road tires use.
- 17 is the wheel diameter in inches.
That means the tire is 225 mm wide, has a sidewall height equal to 65% of that width, uses radial construction, and fits a 17-inch wheel. If one part changes, the tire is not the same size anymore, even if the wheel diameter matches.
Finish With Load Index And Speed Rating
After the size block, you’ll often see something like 102H. This is the service description.
- 102 is the load index. It ties to a chart that lists the maximum weight one tire can carry at the proper inflation level.
- H is the speed rating. It marks the speed class the tire is built to handle under set test conditions.
For a daily driver, this part is easy to miss and easy to get wrong. Two tires can share the same width and wheel size but carry different loads or sit in different speed classes. That’s why a matching size alone is not enough.
Reading A Tire Number When The Sidewall Looks Crowded
After the main size line, the rest of the sidewall adds more clues. You may see letters like XL, M+S, or DOT, plus marks for treadwear, traction, and temperature. Read these as add-ons, not as part of the main size code.
What The Prefix Letters Mean
- P = passenger car tire
- LT = light truck tire
- ST = special trailer tire
- T = temporary spare
- No prefix = often a Euro-metric passenger tire
A trailer tire may look close to a passenger tire on paper, but it is built for a different job. The same goes for temporary spares. If the prefix changes, treat it as a different category, not a swap-in twin.
What DOT Code And Date Tell You
The DOT line shows factory and date details. The last four digits are the one most shoppers care about. A code such as 2324 means the tire was made in the 23rd week of 2024. If you’re buying old stock, that date helps you spot a tire that has been sitting in storage for years.
If you want a clean visual of extra sidewall marks, Michelin’s tire markings page lays out the load, speed, pressure, date, and winter symbols on one sidewall map.
| Sidewall Mark | What It Means | What To Watch |
|---|---|---|
| P | Passenger vehicle tire | Do not treat it like LT or trailer sizing |
| 225 | Width in millimeters | A wider tire may need a different wheel width or clearance |
| 65 | Aspect ratio | A lower number means a shorter sidewall |
| R | Radial construction | Most passenger tires today use this build |
| 17 | Wheel diameter in inches | Must match the wheel exactly |
| 102 | Load index | Must meet or exceed the car maker’s spec |
| H | Speed rating | Do not drop below the required class |
| XL or HL | Extra or higher load version | Often used on heavier cars and EVs |
| DOT 2324 | Made in week 23 of 2024 | Useful when checking tire age before purchase |
Match The Tire Number To Your Car Before You Buy
The tire on the car is not always the one the car left the factory with. That’s why the sidewall should not be your only reference. Check the driver-door placard or owner’s manual. That placard lists the approved size and the cold tire pressure for your specific trim and wheel setup.
The NHTSA tire safety page says the correct tire size is listed on the owner’s manual or the tire and loading label on the driver’s side door edge or post. That is the number to trust when you want a like-for-like replacement.
When The New Tire Number Must Stay The Same
Stick to the placard size when any of these apply:
- You want stock ride quality and stock speedometer behavior
- You’re replacing only one or two tires
- The car is leased
- The wheel size is factory original
- You don’t want clearance or rubbing surprises
When A Matching Size Still Isn’t A Match
Say your door placard calls for 235/45R18 98V XL. A tire marked 235/45R18 94V matches width, sidewall ratio, construction, and wheel diameter. It still falls short on load rating. On a heavier sedan, SUV, or EV, that lower load number is a bad pick even though the size looks right at a glance.
The same caution applies to speed rating. A lower speed class can change heat handling and tire behavior. If your car maker calls for H, V, W, or Y, don’t treat that trailing letter like decoration.
| Sample Tire Code | Plain English Readout | Fit Note |
|---|---|---|
| P215/60R16 95H | Passenger tire, 215 mm wide, 60 profile, radial, 16-inch wheel, load 95, speed H | Typical sedan format |
| 225/45R17 91W | Passenger tire with no prefix, 225 mm wide, 45 profile, 17-inch wheel, load 91, speed W | Common Euro-metric layout |
| LT265/70R17 121/118S | Light truck tire, 265 mm wide, 70 profile, radial, 17-inch wheel, heavy load service, speed S | Not a direct stand-in for a passenger tire |
| T125/70D17 98M | Temporary spare, 125 mm wide, 70 profile, diagonal build, 17-inch wheel, load 98, speed M | Spare use only |
| ST205/75R15 107/102L | Trailer tire, 205 mm wide, 75 profile, radial, 15-inch wheel, trailer load service, speed L | For trailers, not tow vehicles |
Tire Marks People Misread All The Time
Max Pressure Is Not Your Daily Pressure
The sidewall may say Max Pressure 51 PSI. That is not the air pressure you should pump into the tire for normal driving. It is the tire’s upper rated pressure under set load conditions. Your daily cold pressure usually comes from the door placard, and that number is often lower.
UTQG Is Not A Snow Rating
You may also see treadwear, traction, and temperature grades on passenger tires. Those grades are useful when comparing tires in the same broad class. They do not replace the main size, load index, or speed rating. They also do not tell you that a tire is fit for severe winter use. For that, look for the three-peak mountain snowflake symbol.
Same Diameter Doesn’t Mean Same Tire
A 17-inch tire fits a 17-inch wheel. That sounds simple, yet plenty of shoppers stop there. A 225/65R17 and a 245/45R17 both fit a 17-inch wheel, but they differ in width and sidewall height. One may clear the fender and suspension. The other may not. Ride comfort, steering feel, and gearing feel can shift too.
A Fast Way To Decode Any Tire In Under A Minute
- Find the largest letter-number string on the sidewall.
- Read the prefix first: P, LT, ST, T, or no prefix.
- Read the width, then the aspect ratio, then the construction letter, then the wheel diameter.
- Read the load index and speed rating after the size.
- Check the door placard and make sure the new tire meets that size and service description.
Once you’ve done that a few times, the code stops looking random. You can scan a tire rack, an online listing, or a sidewall photo and know right away whether the tire belongs on your car, your truck, your trailer, or nowhere near any of them.
The Parts That Matter Most For Everyday Driving
If you only remember three pieces, make them these: the full size code, the load index, and the speed rating. Width and wheel diameter tell you if the tire can fit. Load index and speed rating tell you if it can do the job safely on your vehicle. Then the DOT date, winter symbols, and UTQG grades help you judge age and use case.
Read the full line, match it to the placard, and treat every letter as there for a reason. That simple habit cuts through the clutter and makes tire shopping a lot less guesswork.
References & Sources
- Michelin USA.“How to Read Tire Markings and Sidewall Codes.”Used here for sidewall code elements such as width, aspect ratio, construction type, load rating, speed rating, pressure marking, and date code.
- National Highway Traffic Safety Administration (NHTSA).“Tire Safety Ratings and Awareness.”Used here for the driver-door placard and owner’s manual advice when checking the correct tire size for a vehicle.