Decoding the numbers on your tires
Decoding the numbers on your tires
At SVG, when you buy 2 tires, you get 2 free! No joke! When you pay for your first two tires plus alignment, mount and balance fees, you’ll get 2 tires free. When you make an appointment to have the new tires installed, you’ll need to know the correct tire size for your vehicle. You can find the correct tire size for your vehicle in its owner’s manual or on the tire placard in your driver’s side door jamb.
But what do all of those numbers mean?
The numbering system on the tire wall can be confusing. Let’s decode those numbers to help you understand what you need:
Tire Type
The first letter in the code tells you what class of tire it is.
- P stands for passenger vehicle tire. P-class tires include cars, SUVs, crossovers, minivans and smaller pickup trucks.
- LT stands for light truck. Tire sizes beginning with LT are designed for light trucks. They will have higher psi recommendations to better support heavier loads and trailers.
- ST stands for Special Trailer. These tire sizes are designed for trailers, including fifth wheels and other travel trailers, as well as boat and utility trailers.
If there is no letter before the first number, you have a metric tire most commonly referred to as European size. It is also measured in millimeters but may have a different load capacity than a P or LT tire.
Tire Width
The three-digit number following the tire type letter is the tire’s width (from side to side, looking at the tire head on) in millimeters. This may also be referred to as the section width.
Aspect Ratio
The forward slash separates the tire width number from the two-digit aspect ratio. The bigger the aspect ratio, the bigger the tire’s sidewall will be.
Construction
The following single letter tells you about the construction of the tire’s internal layers (or casing).
- R – Radial
- D – Diagonal
- B – Belted
Wheel Diameter
The following two-digit number is the diameter of the wheel in inches.
Load Index
The next two- or three-digit number after the space is the tire’s load index. The load index tells you how much weight the tire can support when properly inflated. Load indices range from 75 – 105 for passenger tires, with each numeric value corresponding to a certain carrying capacity. The carrying capacity for each value can be found on a load index chart. On passenger tires, the load index is usually found paired with a speed rating and you typically won’t find it on the tire by itself.
Speed Rating
The last letter is the tire’s speed rating. Just as your load index number corresponds to a particular load, your speed rating letter corresponds to a particular speed capability based on a standardized laboratory test. For example, a tire with a speed rating of “S” is rated for up to 112 mph. Regardless of the speed rating capability, it is not recommended to exceed speed limits; and tire speed ratings do not imply that the vehicle can safely be driven at the speed for which the tire is rated.