Car Automotive

Archive for October 1st, 2009

Most highway rims look alike, but all vary somewhat in certain construction features. Variances between rims of different types make part mixing hazardous. A close, proper fit between rim parts is essential to long tire life as well as operating safety.

Although side rings, flanges, and lock rings of different types appear to be properly seated, difficult to detect gaps are often present.The illustrations in Figure 3.10 show correct, safe matchings of rim parts. Mismatched rings and bases, which almost always create an unsafe operating condition are also shown. For more information, refer to Department of  Transportation (DOT) Multipiece Rim/Wheel Matching Chart.

Mismatched duals have the same effect on the life of tires as low inflation or overload. An underinflated tire on a dual assembly shifts its share of the load to its mate, which then becomes overloaded and frequently fails prematurely. A difference of 15 psi inflation may result in the lesser inflated tire supporting 500 pounds less than the tire with the proper inflation. A similar action occurs when one tire’s diameter is smaller than its mate. A difference of 1/4 inch in diameter may result in the larger tire carrying 600 pounds more than the smaller.

The shift in load becomes more prevalent as the difference in diameters or inflation becomes greater. Improperly matched duals are subject to rapid treadwear because the larger tire carries more load and will wear fast .Although the mismatched duals have different diameters, they must rotate at the same speed. The smaller tire then also wears unevenly because it is forced to scuff over the road. The overall result is abnormal and unequal treadwear for both tires. Improperly matched duals may also lead to sudden air loss as a result of one tire being required to flex severely in doing more than its share of the work.