Ever wonder what the numbers and letters on the sidewall of the tire mean? No, they aren’t special lottery numbers. The tire sidewall information describes three things: the type of tire, the size of tire, and specific details of the tire. Here is a break-down of what the designated numbers and letters mean.
Manufacturer Specific Information
- Brand name – like Cooper, Goodyear, Michelin, etc.
- Model name – like Evolution H/T, Scorpion Verde, etc.
- Type of Tire. Example: P225/70R16 91S
The very first letter or letters listed on the tire sidewall information means what type of vehicle the tire is for.
“P” = Passenger Car – The Tire and Rim Association defines passenger vehicles to include cars, mini-vans, SUV’s and other light duty pickup trucks (1/4 ton or ½ ton capacity). The P designation is the most common type of tire.
“LT” = Light Truck – Designated for vehicles capable of carrying heavy cargo or pulling trailers. Weight capacity is equal to ¾ ton to 1-ton capacity. There are three light truck designations – numeric, wide base and flotation. Numeric is for heavy cargo or to tow trailers. Wide base is for heavy cargo loads or tow trailers on a wheel rim with a diameter of 16.5 inches. The final designation, flotation is for over-sized tires to carry heavy cargo loads or tow trailers on loose surfaces.
“T” = Temporary – Designated for spare tires.
“ST” – Special Trailer – Only to be used on car, boat or utility trailer.
- Tire Width. Example: P225/70R16 91S
The three-digit number after the letter designation is for the width, in millimeters. The width always refers to the measurement from one sidewall to the other sidewall.
- Aspect Ratio. Example: P225/70R16 91S
The forward slash separates the Tire Width from the Aspect Ratio. The Aspect Ratio is the ratio of the height of the tire’s cross-section to its width.
- Wheel Diameter. Example: P225/70R16 91S
Two-digit number after the Construction Type designation that specifies wheel diameter in inches or how wide the wheel is across the center. The 16 in the information means the tire should be matched to a 16-inch diameter wheel.
- Construction Type. Example: P225/70R16 91S
The single letter after the Aspect Ratio indicates the internal construction of the tire.
R = Radial – Internal body plies of the tire radiate outward from the center.
D = Diagonal – Internal body plies of the tire crisscross on a diagonal pattern
B = Bias – Internal body plies on the tire crisscross on a diagonal pattern, but there is also an extra layer of reinforcing belts under the tread area. Rarely seen today.
The difference between Radial and Diagonal constructed tires is flexibility. Radial tires are more flexible while Diagonal are more rigid.
In addition, Radial tires have a larger contact area with the ground that provide better steering and contact with the road. Additional benefits of radial tires are better driving comfort, energy efficient, low heat generation at higher speeds, and longer lifespan. While the radial tires have some great benefits, they are generally a more expensive purchase and the flexible sidewall makes it more vulnerable than the Diagonal tires.
Diagonal tires are better suited for rough surfaces as they are designed with solid sidewalls. This in turn creates lower driving comfort and the distortion and heat at higher speeds generate more friction.
Tire Load and Performance
- Load Index. Example: P225/70R16 91S
Two or three-digit number that follows the space after the Wheel Diameter. The load ratings tell you how many pounds a tire can safely carry. The load index goes from 71 to 110 with the higher the number the more weight the tire can support. Check the Load Index chart by clicking here.
- Performance Rating. Example: P225/70R16 91S
The last letter in the tire size sequence represents the Performance Rating. This rating designates a top speed in which the tire has been approved for safe travel for a sustained amount of time based on a standardized laboratory test. Check the Performance Rating by clicking here.
Where to Find Your Tire Size
Finding the manufacturer recommended tire size for any vehicle is as easy as looking at the tire itself. You can find the information in the following four locations:
- Your owner’s manual
- The driver’s side door jamb
- Inside your glove box door
- Within your gas tank hatch
How to Determine the Age of Your Tires
All tires manufactured after 2000 have a code printed on them that starts with the letters “DOT”, followed by a series of 10-12 characters. The U.S. Department of Transportation (DOT) requires this code on all tires. The last 4 digits designate the week and year of the manufacturing date.
In the example, the code: DOT U2LL LMR 3609
The 3609 provides you with the detailed information. The first two digits (36) mean it was manufactured during the 36th week of the year. The last two digits (09) reference that the year was 2009.
Register Your Tires
Once you have new tires make sure the tires are registered with the manufacturer. This will ensure the record of your purchase for warranty issues and if a safety recall is needed. A few quick steps can save you later. Take a look at your tire sidewall information and write down your DOT. Then go to the manufacturer website and enter your information. The manufacturer will verify your purchase and you will be registered in a matter of minutes.
Your local Tire Discounters welcomes you to stop by for a consultation on tires and what the numbers mean to you and your driving habits. You can make an appointment today!