2008 BMW Z4 M Series Owner's Manual - Page 89
2008 BMW Z4 M Series Manual
Page 89 highlights
All passenger car tires must conform to Federal Safety Requirements in addition to these grades.< Tread wear The tread wear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and one-half, 1 γ, times as well on the government course as a tire graded 100. The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate. RSC: Run-Flat Tires Run-Flat tires are labeled on the sidewall with a circular symbol containing the letters RSC. Refer to page 88. M+S Winter and all-season tires. These have better winter performance properties than summer tires. Traction The traction grades, from highest to lowest, are AA, A, B and C. Those grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. A tire marked C may have poor traction performance. The traction grade assigned to this tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics.< Tire condition Inspect your tires frequently for tread wear, signs of damage and for foreign objects lodged in the tread. Check the tread depth. Minimum tread depth The tread depth should not drop below 1/8 in/ 3 mm, although, for example, European legislation only specifies a minimum tread depth of 1/16 in/1.6 mm. At tread depths below 1/8 in/ 3 mm there is an increased risk of high-speed hydroplaning, even when only small amounts of water are present on the road surface. When winter tires wear down past a tread depth of 1/6 in/4 mm, they become perceptibly less suitable for winter conditions. In the interest of safety, new tires should be installed. Driving tips Reference Mobility Wear indicators in the base of the tread groove are distributed around the tire's circumference; 87 Temperature The temperature grades are A, the highest, B and C, representing the tire's resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause the material of the tire to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a level of performance which all passenger car tires must meet under the Federal Motor Vehicle Safety Standard No. 109. Grades B and A represent higher levels of performance on the laboratory test wheel than the minimum required by law. Online Edition for Part no. 01 41 0 014 500 - © 08/07 BMW AG Controls At a glance The temperature grade for this tire is established for a tire that is properly inflated and not overloaded. Excessive speed, underinflation, or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure.