How to Read Tire Sizes - Complete Guide

🔍 Understanding Tire Size Codes

Example Tire Size:

P 225/55 R 17 97 H

This tire size contains 6 key pieces of information

Tire Type

P = Passenger
LT = Light Truck
ST = Special Trailer
T = Temporary

Width

225

Tire width in millimeters from sidewall to sidewall

Aspect Ratio

Sidewall height as percentage of width (55% of 225mm)

Construction

R = Radial
D = Diagonal
B = Belted

Wheel Diameter

Rim diameter in inches that the tire fits

Load Index

Maximum weight capacity (1,609 lbs for index 97)

Speed Rating

Maximum safe speed (H = 130 mph)

📏 Tire Measurements Explained

🔢 Tire Width

Measurement:Millimeters
Location:Sidewall to sidewall
Common Range:125-425mm
Example:225mm = 8.86 inches

Wider tires typically provide better grip but may increase road noise and fuel consumption.

📐 Aspect Ratio

Measurement:Percentage
Calculation:(Height ÷ Width) × 100
Low Profile:30-50%
Standard:55-70%
High Profile:75-85%

Lower aspect ratios provide better handling but a firmer ride.

⭕ Wheel Diameter

Measurement:Inches
Common Sizes:13" to 22"
Performance:17" to 20"
Off-Road:15" to 17"

Larger wheels allow for bigger brakes but may reduce ride comfort.

⚖️ Load Index Reference

Load Index Chart (Most Common)

75: 387 kg (853 lbs)
80: 450 kg (992 lbs)
85: 515 kg (1,135 lbs)
90: 600 kg (1,323 lbs)

91: 615 kg (1,356 lbs)
95: 690 kg (1,521 lbs)
100: 800 kg (1,764 lbs)
105: 925 kg (2,039 lbs)

110: 1,060 kg (2,337 lbs)
115: 1,215 kg (2,679 lbs)
120: 1,400 kg (3,086 lbs)
125: 1,650 kg (3,638 lbs)

🏎️ Speed Rating Guide

Common Speed Ratings

S: 112 mph (180 km/h)

T: 118 mph (190 km/h)

H: 130 mph (210 km/h)

V: 149 mph (240 km/h)

W: 168 mph (270 km/h)

Y: 186 mph (300 km/h)

Important Notes

Never exceed the speed rating
Match or exceed original rating
Higher ratings often mean better handling
Consider your driving conditions

🔧 Real-World Examples

Example 1: Compact Car

195/65R15

P195/65R15 91H

• Width: 195mm (7.7 inches)

• Sidewall: 127mm (65% of 195mm)

• Wheel: 15 inches

• Load: 1,356 lbs per tire

• Speed: Up to 130 mph

Example 2: SUV/Truck

LT265/70R17

LT265/70R17 121S

• Type: Light Truck

• Width: 265mm (10.4 inches)

• Sidewall: 186mm (70% of 265mm)

• Wheel: 17 inches

• Load: 3,197 lbs per tire

• Speed: Up to 112 mph

Example 3: Performance Car

245/40R18

245/40R18 97Y

• Width: 245mm (9.6 inches)

• Sidewall: 98mm (40% of 245mm)

• Wheel: 18 inches

• Load: 1,609 lbs per tire

• Speed: Up to 186 mph

📅 Additional Tire Markings

📅 DOT Date Code

Example: DOT...2423

24:24th week of year
23:Year 2023
Age Limit:6 years maximum
Location:Sidewall near rim

🏷️ UTQG Ratings

Uniform Tire Quality Grading

Treadwear:200-800+ rating
Traction:AA, A, B, C
Temperature:A, B, C
Higher = Better:Performance

❄️ Special Markings

M+S:Mud and Snow
3PMSF:Severe Snow Service
XL/RF:Extra Load/Reinforced
BSW/WSW:Black/White Sidewall

🔧 Ready to Calculate?

Now that you understand tire sizes, use our professional tire size calculator to compare different options, check speedometer effects, and find the perfect fit for your vehicle!

🔧 Use Tire Calculator 🛡️ Safety Guide

📖 How to Read Tire Sizes