Useful Information about Tire Size

Understanding tire size symbols may always be a hassle for many. But you just need a little explanation of the numbers and letters on your tire’s sidewall and it will give you all the information about your tire’s type, size and performance. Here are some tips.

Type of Tire

You’ll see the letter “P” at the start of the “Tire Size”. It tells you that the tire is P-Metric which means that the tire is made to some standards within the USA, meant for passenger vehicles.

If there is no letter at the start, it means that it’s a Euro metric tire. It has a different load capacity than P-Metric tires.

If there are letters “LT” at the start or end of the tire size, it means that the tire was made for light trucks. These tires often need higher inflation pressures than passenger tires.

Refer to your tire placard or owner’s manual for the recommended size and inflation pressure for your tire. Another good source to find the perfect tire size is tiresizehelp.com.

car tire size tips

Width of Tire

Tire width is measured from sidewall to sidewall in millimeters. The first three digits in the tire size indicate the tire width. E.g. if your tire size is P215/65 R15, your tire’s width is 215 millimeters.

Aspect Ratio

This is the ratio of the tire’s cross-section’s height to its width. It is indicated as a 2-digit number after the slash mark in the tire size. Thus in the number P215/65 R15, the number 65 is the aspect ratio i.e. the height is 65% of the tire’s width. Thus, the higher the aspect ratio, the bigger will be the tire’s sidewall.

Construction

The letter “R” in the tire size number indicates “Radial” which means that the layers run radially throughout the tire.

Diameter of Wheel

This is the size of the wheel from one end to the other. It indicates the size of the wheel the tire can fit. Thus the tire with size P215/65 R15 is made to fit a wheel with a 15” diameter.

Load Index

This shows the maximum load the tire can bear when inflated properly. You’ll find it on the tire sidewall in pounds as well as kilograms.

Speed Rating

This shows the maximum speed capability of the tire. Usually it is matched to the vehicle’s maximum speed capability.

DOT Symbol

DOT symbol is on the sidewall of the tire and shows that the tire is compliant with all Federal Motor Vehicle Safety Standards in the USA.

Hopefully this information will reduce your confusion about the tire size and you can choose the proper sized tire for your vehicle. Happy tire shopping!

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