How to Read Tire Size Numbers: Complete Guide.

Understanding what tire size numbers mean is essential for buying the right tires for your vehicle. This guide explains how to read tire sizes, decode tire markings, and find the correct tire size for your car, SUV, or pickup truck.

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What Do Tire Size Numbers Mean?

Most passenger vehicles use a three-part tire size format. Each number in your tire size tells you specific measurements:

1. Tire Width (measured in millimeters)
2. Aspect Ratio (sidewall height as a percentage)
3. Wheel Diameter (measured in inches)

How to Read Tire Size: Real Example

Example tire marking: 255/45 R20

Here's what each tire size number means:

• 225: The tire width is 225 millimeters from sidewall to sidewall
• 45: The tire sidewall height equals 55% of the tire's width (102.5 mm in this example)
• 20 The tire fits a 16-inch diameter wheel

When shopping for replacement tires online, search for: 225/45 R20 (the "R" indicates radial tire construction, standard for modern tires).

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Understanding Tire Service Description Codes

The alphanumeric code following your tire size (like "91V") is the service description. This tire marking indicates:

• Load Index (91): Maximum weight capacity per tire
• Speed Rating (V): Maximum safe speed capability
• Heat resistance and performance characteristics such as Mud and Snow (M/S) and Three-peak Mountain Snowflake (3PMSF) rating.

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Where to Find Your Car's Tire Size

How to find the correct tire size for your vehicle:

Check these three locations for manufacturer recommended tire sizes:

• Driver's door jamb sticker (most common spot to find tire size information)
• Fuel door or gas cap area
• Vehicle owner's manual (tire specifications section)

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Why Correct Tire Size Matters

Installing the wrong tire size affects:

• Vehicle handling and safety
• Speedometer accuracy
• Fuel efficiency
• Suspension wear
• Warranty coverage

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Quick Tire Size Tips

• Always replace tires with the manufacturer's recommended size
• The tire placard shows both standard and optional tire sizes
• All four tires should typically match in size and type
• Consult a tire professional if considering different tire sizes

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Need help finding your tire size? Check your current tire sidewall markings or use TireTutor's vehicle tire search finder tool to ensure you're ordering the correct tires for your vehicle.

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