A tire’s service description is the load index and speed symbol that show how much weight the tire can carry and the speed category it fits.
When you spot a sidewall code like 225/45R17 94W, the service description is the last part: 94W. That short code tells you two things at once. The number is the tire’s load index, and the letter is its speed symbol.
Tire size alone does not tell the whole story. Two tires can share the same size and still be built for different weights and speed classes.
Service Description On A Tire Sidewall And Why It Matters
The service description sits right after the size on many passenger tires. In a code such as 215/55R17 94V, the service description is 94V. Read it as one pair, not as two random marks.
The load index is a numeric code tied to the maximum weight one tire can carry when it is inflated and used as rated. The speed symbol is a letter tied to the tire’s maximum speed category under set test conditions. Put together, they help you match the tire to the car.
Many drivers stop at width, aspect ratio, and wheel diameter. The service description is smaller, but it is the part that keeps the tire in the right load and speed class for the vehicle.
Where You’ll See It On The Sidewall
On many passenger tires, the pattern looks like this: P215/55R17 94V. The service description comes after the rim size. On light-truck or van tires, the wording can get a bit denser, and some tires may show dual load indexes or extra markings. The same idea still applies: the short code near the size tells you the tire’s load and speed rating.
How To Read A Real Example
Take 225/45R17 94W. Here’s the plain-language breakdown:
- 225 = tire width in millimeters
- 45 = sidewall height as a percentage of width
- R = radial construction
- 17 = wheel diameter in inches
- 94 = load index
- W = speed symbol
Michelin’s load rating and speed rating page lays it out the same way: the load rating and speed rating together make up the service description. Once you know that, the sidewall starts to read like a label instead of a puzzle.
| Marking | What It Means | Why You Care |
|---|---|---|
| P | Passenger-tire type on many U.S. sidewalls | Shows the tire class the size belongs to |
| 225 | Section width in millimeters | Needs to fit the wheel and vehicle setup |
| 45 | Aspect ratio | Affects sidewall height and ride feel |
| R | Radial construction | Nearly all modern road tires use this design |
| 17 | Wheel diameter in inches | Must match your wheel exactly |
| 94 | Load index | Tells how much weight one tire is rated to carry |
| W | Speed symbol | Tells the tire’s speed category |
| M+S or 3PMSF | Snow or winter-use marking | Separate from service description |
| DOT code | Factory and production date details | Helps you check tire age |
Why The Service Description Is Not Just Fine Print
If the load index is too low, the tire may be asked to carry more than it was rated for. If the speed symbol is too low, the tire may not match the speed class the vehicle maker called for.
Going higher is often allowed, but it does not raise the vehicle’s own limits. A tire with a higher load index does not let the car carry extra cargo beyond the vehicle placard. A higher speed symbol does not turn a family sedan into a track car either. The vehicle still sets the ceiling.
NHTSA’s tire safety page stresses sticking to the vehicle maker’s size and load limits. That’s the smart place to start when you’re checking replacement tires, since the door-jamb placard and owner’s manual tell you what the vehicle was built to use.
What To Check Before You Buy
- Read the driver-door placard for the original tire size and pressure.
- Match the load index to the original rating or go higher if the maker allows it.
- Match the speed symbol to the original rating unless a winter-tire setup calls for a different choice.
- Keep the same service description across an axle unless the vehicle maker says otherwise.
- Do not assume two tires are equal just because the size line matches.
Common Load Index And Speed Symbol Examples
A compact car might wear something like 91H. A sporty sedan may use 94W. A heavier crossover could land on 100H or 104V. The tire size may look familiar across all three, yet the service description shifts with the vehicle.
| Service Description | Plain Meaning | Typical Read |
|---|---|---|
| 91H | Load index 91, speed symbol H | Common on smaller cars |
| 94V | Higher load than 91, faster speed class | Seen on many midsize cars |
| 94W | Same load as 94V, higher speed class | Common on sportier trims |
| 97H | More carrying capacity, H speed class | Used on some wagons and crossovers |
| 100H | Heavier load class with H symbol | Seen on many crossovers |
| 104V | High load class with V symbol | Common on larger SUVs |
You do not need to memorize every number-letter pairing. You just need to know what the pair is doing. The number handles carrying capacity. The letter handles speed class. Read both before you order tires online or approve a replacement at the shop.
What The Service Description Does Not Tell You
This is where many drivers get crossed up. The service description is not the treadwear grade. It is not the traction or temperature grade. It is not the tire’s age, load range, tread pattern, or winter symbol. Those live elsewhere on the sidewall.
That distinction matters when you compare tires. One tire can have the right service description and still be a poor fit for your weather, ride preference, or driving style. Another tire can have a strong treadwear grade but the wrong load index. You need the whole sidewall story, not one line in isolation.
Marks That People Mix Up
- UTQG grades: treadwear, traction, and temperature marks for many passenger tires
- Load range: a different marking common on truck tires
- DOT date code: tells when the tire was made
- XL or Extra Load: shows a tire built to carry more at a given size when used as specified
- M+S or 3PMSF: marks tied to mud, snow, or winter service
Mistakes That Lead To The Wrong Tire
One common slip is shopping by size only. Another is assuming a lower service description is close enough because the car is “just used around town.” Tire ratings are not decoration. They are part of the fitment data.
A second slip is mixing different service descriptions on the same axle after a single tire failure. That can leave the car with uneven load or speed capability side to side.
A third slip is missing special cases. Some winter tires use a lower speed symbol than the original all-season or summer tire. Some light-truck tires show two load indexes, one for single fitment and one for dual fitment. If your sidewall looks more complicated than the usual passenger-car line, slow down and match it to the vehicle placard before you buy.
A Three-Step Check Before You Order
- Read the full sidewall on the tire you have now, including the service description at the end of the size line.
- Compare it with the driver-door placard or owner’s manual, since the vehicle maker’s spec is the one that counts.
- If you want a different tire model, keep the service description at the same level or move up only when the fitment allows it.
Once you know where the service description sits and what each part means, tire shopping gets a lot less murky. That tiny code after the size line tells you whether a tire truly matches your vehicle or only looks close at a glance.
References & Sources
- Michelin.“Tire Load Rating & Speed Rating Explained.”Explains that a tire’s service description is the load rating and speed rating shown on the sidewall.
- National Highway Traffic Safety Administration.“Tire Safety Ratings and Awareness.”Provides official tire safety information, including sidewall ratings, load limits, and replacement guidance.