Decoding a sidewall starts with one fact: understanding 225/55R18 tire ratings means keeping two separate codes apart. The 225/55R18 portion is pure size. The number-and-letter pair printed after it, often written as 98H, tells you how much weight the tire can carry and the top speed it can sustain under load.
What Does 225/55R18 Mean?
225/55R18 is a size code, not a performance code. Each part names a dimension:
- 225 – section width in millimeters
- 55 – aspect ratio, meaning sidewall height is 55% of section width
- R – radial construction
- 18 – diameter of the wheel it mounts on, in inches
What Do Load Index And Speed Rating Mean?
The service description is the code directly after the size. On a 225/55R18 98H, the 98 is the load index and the H is the speed rating. They are two separate ratings, not one combined spec.
The load index is a numeric code for the tire’s maximum load when properly inflated. It is not a direct pound measurement, so a chart is needed for translation. A higher number means more carrying capacity.
The speed rating is the letter after the load index. It marks the maximum sustained speed the tire is designed for under specified load and inflation conditions. H is a common passenger-car rating, but tires in the 225/55R18 class also appear with V, W, and Y codes.
| Speed Rating | Maximum Sustained Speed |
|---|---|
| H | 130 mph |
| V | 149 mph |
| W | 168 mph |
| Y | 186 mph |
| Z | Historical rating for 149+ mph; W and Y now cover those speeds |
That rating only means something when the tire is correctly inflated and not overloaded. Run a speed-rated tire underinflated or overloaded and the rating no longer applies in real-world use.
Matching The Ratings On A Replacement Tire
Replacement rules come down to one requirement: meet or exceed the size, load capacity, and speed rating your vehicle specifies. The driver’s door placard and owner’s manual are the final authority, not the tire currently on the wheel.
When you shop, compare the full service description, not just the 225/55R18 size. All 225/55R18 tires are not equal. One model may carry a 98H while another uses a 94V, and those two tires differ in both weight capacity and speed capability. If the vehicle requires a minimum load index of 98, fitting a tire with a lower index is a downgrade. The same logic applies to speed rating: match or exceed the vehicle specification.
Read the sidewall before comparing anything, use a load-index chart to translate the number, and verify wheel width compatibility before mounting. Goodyear’s load-index and speed-rating guide is a solid reference for converting index numbers to pounds.
When you move from specs to shopping, our ranking of the best 225/55R18 all-season tires compares real-world traction, ride comfort, and treadwear side by side.
FAQs
Do all 225/55R18 tires carry the same load index and speed rating?
No. 225/55R18 is only the physical size, and tire makers attach different service descriptions to that size. One model may use a 98H code while another uses a 94V or something entirely different. Always read the sidewall service description before comparing two tires, since carrying capacity and top-speed capability vary by model.
What does 98H mean on a tire?
98H is the service description: load index 98 and speed rating H. Load index 98 maps to a specific maximum load in pounds when the tire is inflated to its rated pressure. The H means the tire is built to sustain speeds up to 130 mph under those same conditions. Overloading or underinflating the tire cancels out the rating.
Can I use a lower speed rating than my vehicle specifies?
No. Replacement tires should meet or exceed the load capacity and speed rating listed in the owner’s manual and on the driver’s door placard. Fitting a lower-rated tire can push the tire beyond its design limits during normal driving. Choosing a higher speed rating is fine, but it does not increase how much weight the tire can carry.
References & Sources
- Goodyear. “Load Index Speed Rating.” Explains load-index and speed-rating definitions and references used in this article.