Reading a tire chart (more commonly understood as reading the markings on a tire's sidewall) involves understanding the alphanumeric code that provides crucial information about the tire's size, load capacity, speed rating, and more. Here's a breakdown:
Understanding the Tire Code
Let's use a common tire code as an example: P225/50R17 94V
Each component provides different information:
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P: (Optional) Indicates the type of vehicle the tire is designed for.
- P - Passenger Tire (typically for cars, minivans, SUVs)
- LT - Light Truck Tire (for pickup trucks, vans, and SUVs designed for heavier loads)
- If no letter precedes the size, it's likely a European metric tire. These tires have slightly different load-carrying capacities compared to P-metric tires.
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225: Tire Width. This number indicates the tire's width in millimeters from sidewall to sidewall. In this case, the tire is 225 mm wide.
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50: Aspect Ratio. This is the ratio of the tire's sidewall height to its width, expressed as a percentage. Here, the sidewall height is 50% of the tire's width. So, the sidewall height is 50% of 225 mm.
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R: Construction Type. This letter indicates the type of internal construction of the tire. "R" stands for Radial, which is the most common type of tire construction.
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17: Rim Diameter. This number indicates the diameter of the wheel rim in inches that the tire is designed to fit. This tire fits a 17-inch wheel.
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94: Load Index. This number represents the tire's maximum load-carrying capacity when properly inflated. You'll need to consult a load index chart to determine the actual weight this number represents. For example, a load index of 94 corresponds to a load capacity of 1477 lbs (670 kg). Always refer to a reliable load index chart like the one found on the Tire Rack website (https://www.tirerack.com/upgrade-garage/what-is-a-tire-load-index-chart).
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V: Speed Rating. This letter indicates the maximum speed the tire is designed to sustain for extended periods. Each letter corresponds to a specific speed in mph and km/h. The "V" rating means the tire is rated for speeds up to 149 mph (240 km/h). Never exceed legal speed limits. Consult a speed rating chart for more information; resources such as the one from SimpleTire (https://simpletire.com/information/tire-speed-rating) are good references.
Other Important Markings
Besides the core tire code, look for these additional markings:
- DOT (Department of Transportation) Code: Indicates the tire meets U.S. safety standards and also reveals the tire's manufacturing date. The last four digits typically represent the week and year the tire was manufactured. For example, "1223" means the tire was manufactured in the 12th week of 2023.
- M+S (Mud and Snow): Indicates the tire is designed for use in muddy or snowy conditions.
- Three-Peak Mountain Snowflake (3PMSF) Symbol: Indicates the tire meets specific snow traction performance requirements. These tires offer superior snow performance compared to M+S tires.
- Maximum Inflation Pressure: The maximum air pressure the tire can hold. Do not exceed this pressure.
- Maximum Load: The maximum weight the tire can carry when properly inflated.
- Treadwear, Traction, and Temperature (UTQG) Ratings: These ratings provide information about the tire's relative tread life, wet traction, and heat resistance. These are useful, but can be manufacturer-specific and should only be compared within the same brand.
Where to Find Tire Information
- Tire Sidewall: The most comprehensive source of tire information.
- Vehicle Owner's Manual: Provides the recommended tire size and pressure for your vehicle.
- Tire Placard: Usually located on the driver's side doorjamb, this placard provides the original equipment tire size and recommended inflation pressure.
By understanding these markings, you can effectively "read" a tire chart (sidewall) and make informed decisions about tire selection and maintenance.
