PCR Tire-School
Tire Size
Tire size is defined by bead shape, width, diameter and other parameters, which become firm and are used worldwide due to the European Tire and Rim Technical Organization (ETRTO) and the US Tire and Rim Association (T&RA). Both use a partially metric-based system. Virtually all passenger tires use the rim and tire sizing, load and inflation system stipulated by ETRTO and T&RA.
- Tire Ply Composition & materials used
- Max cold inflation & load limit
- UTQG Rating
It indicates a passenger car tire. If the first character in the size designation is a “P,” the tire is engineered to standards set by the T&RA. In case of no “P”, the tire is engineered to ETRTO standards and is a metric tire. The standards set by T&RA and ETRTO have evolved together and are in fact interchangeable.
It indicates the tire section width in millimeters. The section width will be larger on a wider rim and smaller on a narrower one. Therefore, each tire is mea- sured to specific rim width.
It compares the tire’s inflated section height, which is the distance from the bead to the tread, to its section width (maximum). An aspect ratio of 65 means that the tire’s section height is 65% of the tire’s section width.
It indicates the type of ply construction in the tire’s casing or carcass.”R” means radial. “D” means diagonal, referring to bias ply tires.”B” means belted for belted-bias ply tires. Never mix radial tires with any other differently-con- structed tires on a vehicle.
It is an alphanumeric combination, consisting of two parts, a number and a letter. In this example, “94” is the load index, which represents that the load carrying capacity of the tire is 670kg. The letter “H” is the speed symbol, which means the speed limit of the tires is 130 mph (210kph) at the load specified by the load index. Toyomoto does not recommend the use of any of its products in excess of the specified speed limits.
NOTE: Tire speed ratings must exceed the maximum speed capability of the vehicle to which they are fitted. It is important to remember this when replacing the tires on your vehicle. Replace tires with equivalent or higher speed rated tires.
Some tires have additional markings related to service. An M&S or M+S desig- nation means the tire is suitable for mud and snow use.
ALL-SEASON DESIGNATIONIt means that the tire meets M&S/M+S requirements over- coming the noise and rolling resistance associated with the winter tires with traditional pattern design. The M&S/M+S designation means that the tire is suitable for normal all-weather driving applica- tions. Tires that meet the requirements of the M&S designation have better winter traction compared to those without the M&S symbol.
DOT code number, issued by the NHTSA of USA, molded into the sidewall designates the manufacturer and plant where the tire was produced, and the week and year the tire was manufactured.
All passenger tires are marked on the sidewalls to indicate maximum load capacity and maximum inflation pressure. Truck tires will indicate recommended pressure for maximum loads for both dual and single application. But super-sin- gle tires are exceptional.
All replacements are based on the Original Equipment (OE) tire overall inflated diameter within industry standards and are recommended with load carrying capacities and speed ratings that meet or exceed the needs of the vehicle for normal operation. Depending on the car’s optional equipment, each make and model car may have several OE tire fitments.
To ensure proper tire/rim/vehicle fitment, front and rear, please contact Toyomo- to dealer for recommendation and replacement. Mounting tire in rims can be hazardous. Do not attempt to mount tires on your own. Maintaining adequate clearance is important for safety. Toyomoto dealer must recommend proper tire size by inspecting clearance of vehicle fenders, wheel wells, suspension and brakes while the steering wheel is at full lock and the suspension is fully com- pressed.
To accurately measure the width of a tire, the tire must be mounted on a rim. Since a tire’s section width varies with the rim, each tire is measured on a specific rim.
Correct flex at the designed flex point in a tire sidewall for optimum tire perfor- mance.If the rim is too narrow, the flex point moves toward the shoulder area, which shall cause heat buildup in the shoulder, hence reducing tire life and resulting in failure. If the rim is too wide, the flex point moves towards the rim area, which shall cause the same problem to the tire.
ASPECT RATIO
Aspect ratio is the relationship of a tire’s height to width when mounted and inflated on a correctly-sized rim.
The change in aspect ratio affects section width, which relates directly to the load carrying capacity of the tire. Comparing to the original equipment tire, the load carrying capacity must be maintained or increased. The change of the tire’s overall diameter also has impact to the vehicle’s overall gear ratio, as well as the accuracy of the speedometer and odometer. Tire footprint is also affected by change in aspect ratio and overall diameter. A high aspect ratio tire will have a long, narrow footprint, vice versa.
Besides, tire diameter/aspect ratio affects the input to the engine computers on some new cars, since vehicle speed is an input to these computers.
In other words, tire changes involving changes in aspect ratios should be made in consultation with your Toyomoto dealer and reference to the Owner’s Manual of the vehicle.