Time To Re-Tire?

Anyone who has gone into a tire shop to get new tires knows the people on the other side of the counter speak a language all their own and they don’t bother to let you in on their secret. Before heading to the tire store, read this article and learn the lingo or better yet, bring this article with you when you go. Forewarned is forearmed!

Let’s take a typical tire specification and break it down into the major components. For example, original specifications for the 87 300D were 195/65 SR 15. The 195 refers to the width of the tread (across the tire) in millimeters. The 65 refers to the length of the sidewall but not as one would expect. The 65 is a percentage of the tread width. For a 195/65 tire, the actual sidewall length would be 126.75 Millimeters. By sidewall I mean the length measured from the edge of the wheel rim to the edge of the tread. The S specifies the speed rating of the tire. Referring to the chart below, an S-rated tire can safely withstand a maximum speed of 112 MPH. NOTE: Never buy a tire with a speed rating lower than the maximum speed your Benz can attain, because doing so could cause tire failure at high speed and a major accident. The R refers to the fact that the tire is known as a radial. Almost all tires made today are radials, but in the past that is not true. My 66 Mustang must have bias-ply tires for example. Radials are specified because they have much lower rolling resistance and hence better fuel mileage is obtained. Last but not least, the 15 refers to the diameter of the wheel, measured in inches from one edge of the rim across the center to the other edge of the rim.

Related matters: Balancing. Whenever tires are remounted on rims, they need to be balanced, which refers to the process in which the wheel and tire are spun on a machine to determine heavy and light spots, then small weights are added to the wheel to bring it into dynamic balance. Unbalanced or improperly balanced tires can cause excessive wheel wobble, premature tire wear and vibrations that can be felt throughout the vehicle. Balancing is a MUST whenever new tires are mounted.

This is also a good time to consider getting an alignment, which refers to the angles by which the tires make contact with the road and with respect to each other. Pay particular attention to the tread wear patterns on the OLD tires. If there is nice even wear across the tread and there are no undue vibrations at speed, then an alignment may not be necessary. Your call.

Everyone talks about tire rotation but is it necessary? There are of course two schools of thought on this matter. Some say that rotations are only needed about halfway through the life of the tire, while others say to rotate every 5000 miles. Based only on my experience with my 300E, I found that rotating the tires wasn’t worth all the effort because it didn’t extend the life of my tires. Your mileage may vary of course!

Inflation. Refer either to your Owner’s Manual or to the inflation pressures listed inside the gas (or diesel!) filler door and always check pressures with the tires cold (undriven). NEVER exceed the maximum pressure rating noted on the side of the tire.

Insurance. Tire store staff will try to sell you "insurance" on your tires and want to replace the valve stems. If you value "peace of mind", spend the extra $$ for the insurance and the valve stems and, if not, save your money and buy those neato valve stem caps with the MB logo on them.

Steven Rae, Technical Advisor