Reading Tire Sidewall Codes

The numbers on the sidewall of a tire provide important information about the tire’s size, capabilities, and specifications. We join Mark Simpson in the shop as he takes us through some important numbers to be aware of on your tires and considerations you should make in selecting new tires. Here’s a breakdown of what the sidewall numbers typically mean:

1. Tire Size (Example: 225/50R17)

– 225: Tire Width (in millimeters)
This is the width of the tire from sidewall to sidewall, measured in millimeters.

– 50: Aspect Ratio
This number represents the height of the sidewall as a percentage of the tire’s width. In this case, the height of the sidewall is 50% of the tire’s width. A lower aspect ratio generally means a shorter sidewall, which can offer better handling.

– R: Tire Construction
The “R” stands for radial construction, which is the most common type of tire construction. Other types include “B” for bias-ply.

– 17: Rim Diameter (in inches)
This indicates the diameter of the wheel (rim) that the tire is designed to fit, in inches.

2. Load Index and Speed Rating (Example: 94V)

– 94: Load Index
This is a numerical code that corresponds to the maximum load the tire can support. For example, a load index of 94 means the tire can support 670 kg (1,477 lbs). Higher numbers mean a higher load capacity.

– V: Speed Rating
This letter indicates the maximum speed the tire can safely sustain under its recommended load. For example, “V” indicates a maximum speed of 149 mph (240 km/h). Other common speed ratings include:
S: Up to 112 mph (180 km/h)
T: Up to 118 mph (190 km/h)
H: Up to 130 mph (210 km/h)
Z: Over 149 mph (240 km/h)

3. Tire Type and Usage Indicators

– P or LT: P denotes a Passenger vehicle tire. LT denotes a Light Truck tire, meant for vehicles that carry heavier loads.

– M+S or M&S:
This indicates that the tire is suitable for Mud and Snow conditions, making it an all-season tire.

– 3PMSF (Three-Peak Mountain Snowflake):
This symbol certifies the tire for severe snow performance and winter use.

4. DOT Code (Example: DOT X0 R8 1A 0319)**

– DOT: The Department of Transportation (DOT) certification. The subsequent characters indicate the manufacturer, plant code, tire size, and specific information about the tire. The last four digits (e.g., 0319) indicate the week and year of manufacture. In this case, “03” means the tire was made in the 3rd week of the year, and “19” means it was made in 2019.

5. Treadwear, Traction, and Temperature Ratings (UTQG)

Treadwear: This is a number that indicates how long the tire tread is expected to last compared to a reference tire with a rating of 100. For example, a tire with a 300 treadwear rating is expected to last three times longer than a reference tire.

Traction: This indicates the tire’s ability to stop on wet pavement. Ratings include AA (best), A, B, and C.

Temperature: This represents the tire’s ability to dissipate heat. Ratings include A (best), B, and C. These numbers and letters on the sidewall give you key information about the tire’s dimensions, load capacity, speed capabilities, and other important characteristics for safe and efficient driving of your classic car.