The ubiquitous tire. Without it America would grind to a halt. Tires are on trucks, cars, SUVs, virtually every type of rolling stock in the world. Tires must deal with heat, road hazards like nails, glass and steel while not failing the shock and stress of hitting pot holes at high speed. Even toys have tires. Lego produced 318 million plus tires in 2011, becoming the largest tire manufacturer in the world as awarded by Guinness’s book of records.
Uniform Tire Quality Grade (UTQG)
Tires are rated under the ‘Uniform Tire Quality Grade’ or the UTQG. There is a numeric treadwear rating. The higher the number, the better the tire resists wear and lasts longer. A letter code is the traction rating with AA being the highest and lastly the letter coded temperature rating with ‘A’ being the best. The temperature rates the high-speed performance, like highways running on hot summer road surfaces without catastrophic failure. Highly technical the manufactures conduct their own testing according to standard test procedures. It may give some relative information for determining a tire purchase, but the nuances are difficult to grasp by the average buyer. Consumer ratings and other information indicate an easier to understand tire quality.
Parts of a Tire
The parts of the tire are the tread, the outer circumference surface that is in contact with the road. It is made from elastomer copolymer with usually silica and carbon black added. The tread is molded over a nylon belt or crown over a steel mesh. Cords form the carcass ply and bead and are the component keeping the tire together. The bead has a steel cable core with a low-flex ply rapped around it and the bead is what holds the tire on the rim and provides an airtight seal to the rim. A rubber liner holds in the air in tubeless tires. The sidewalls are the flexible sides of the tire that support the crown and tread and connect to the bead.
Radial, Bias & Bias-Belted Ply Tires
Construction types are radial, bias ply and bias-belted ply. Radials run the plies 90 degrees to direction of travel, or ‘radially’ from the tires center to the other side. Bias plays run the ply at angle relative to the tire center, with multiple ply layers running at an angle to each other. Because of this bias ply, tires have a stiffer sidewall and the tread and sidewalls are interdependent. In radial tires, the sidewalls are independent of the belt and tread. Steel belts have a higher dissipation of heat and run cooler, while the sidewall is more flexible. Radials on pavement outperform the bias ply tires offering lower rolling resistance, higher fuel mileage and a more comfortable ride. Off-road tires are generally steel belted radials with aggressive tread design.
The modern radial tire is very flexible. It grows with the speed of the car; centrifugal forces cause the tire tread to swell. Of course, drag racing slicks run on low tire pressure attempting to maximize the footprint, the area in contact with the surface, and photos show that the sidewalls suck in as the tread area grows. A specialized tire application for sure, but one that illustrates tire profile changes at high revolutions. All tires would be subject to the same forces, but with thicker sidewalls the growth in street tires would be more controlled.
Tire Wear Patterns & What They Mean
Wear patterns of an under inflated tire are around the edges of the thread showing more wear than the center. This is caused by cupping of the tread in contact with the ground. Over inflation wear is in the center of tread while the edges show less wear in comparison. Recommended tire pressure up to about 110 miles per hour, far higher than any legal road speed is 100% recommended pressure. The manufacturers recommended pressure takes tire expansion due to running heat and centrifugal forces into consideration under highway conditions.
What Do the Numbers on Tires Mean?
Information including on the sidewall is the UTQG rating, but the tire size and load and speed ratings are there as well. Tire pressure recommendations in US and Metric are also on the tire. DOT and International code compliance are listed, the manufacturer’s name, if snow rated a relative symbol is present and manufacture original equipment approval symbol. Lastly construction type and materials are listed.
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There is a lot to absorb interpreting tire sidewall information. Take care of your vehicles shoes, for a long and safe ride. If anything should go wrong and you are unfortunate enough to experience a flat tire or blown out tire, call us. Citywide Towing Service can meet all your towing and roadside assistance needs.