Understanding tire sizes helps you choose the right tires for safety, comfort, and performance. Let’s break down what the numbers mean.
What Do Tire Size Numbers Mean?
Tire size appears in a format like this: P225/65R17 102H. Each part gives important information about the tire.
1. Tire Type (P)
The first letter tells you the tire type.
- P means Passenger tire.
- LT means Light Truck.
- No letter often means Euro-metric (standard passenger).
Choose the correct type based on your vehicle class.
2. Tire Width (225)
This is the tire width in millimeters.
It measures the section width from sidewall to sidewall.
Wider tires give more grip but may reduce fuel economy.
3. Aspect Ratio (65)
This number is the sidewall height as a percentage of the width.
In this case, the sidewall is 65% of 225mm.
Lower aspect ratios give sportier handling and a firmer ride.
4. Construction Type (R)
The letter R means Radial construction.
Radial tires are standard on modern vehicles.
You may also see D for bias-ply or ZR for high-speed radials.
5. Wheel Diameter (17)
This is the rim size in inches.
It tells you what size wheel the tire fits.
A 17″ tire only fits a 17″ wheel.
Load Index and Speed Rating (102H)
6. Load Index (102)
This number tells you how much weight the tire can carry.
For example, 102 = 1,874 lbs per tire.
Check your owner’s manual for the correct rating.
7. Speed Rating (H)
The speed rating tells you the maximum speed the tire can safely handle.
H means up to 130 mph (210 km/h).
Never install a lower-rated tire than the factory spec.
Where To Find Your Tire Size
Look for a sticker inside the driver’s door jamb.
You can also check your owner’s manual or the current tire sidewall.
Always match the size unless you’re upgrading with care.
Common Tire Markings and What They Mean
- M+S = Mud and Snow rated
- 3PMSF = Severe snow service (symbol of a snowflake)
- XL = Extra Load
- TWI = Tread Wear Indicator
Knowing these markings helps you pick the right tire for the conditions.
Can You Change Tire Sizes?
Yes, but only within safe limits. Slight changes in width or aspect ratio are fine if the overall diameter stays close to stock. Changing too much affects speedometer accuracy and ABS performance.
Effects of Tire Size Changes
- Wider tires improve grip but reduce fuel economy.
- Larger rims often reduce sidewall height, making the ride harsher.
- Smaller tires may affect handling and safety features.
Always consult a tire expert before switching sizes.
Reading tire sizes is easier than it looks. Once you know what the numbers mean, you can buy tires with confidence. Use the right size to ensure safety, ride comfort, and long tire life.
