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Winter 2009
Published quarterly
Volume 6, Number 1
Tires are pretty simple, right? Well, not exactly. There is far more to know than most people realize. In order to make an informed decision there are several key factors to be considered.
An excellent tire for a minivan may be a very poor tire for a car. A light truck may take a totally different tire from both. Tires are designed to work best with specific applications. Even among car tires there are many speed ratings and tires for different purposes.
When an engineer designs a vehicle, he designs the suspension to accommodate a specific type of tire. For instance, if a performance model is being designed, the tires will be softer, have considerably more belts and are designed for handling. Such a tire will normally wear much faster than a tire designed for a non-performance application.
In contrast, a tire designed for long life may be insufficient to handle the loads imposed by the performance suspension. It may handle improperly and may fail in use, creating a safety hazard. Braking and handling can be affected by an improper tire choice. Even though a quality brand is installed, it needs to be the proper tire for the application.
This is why replacing tires with the proper size, rating and style is so important. Selecting the same brand name and even size, as the original tire will not insure you get the proper replacement. Tire makers often produce several different tire applications in each size.
A place to start is with the tire placard. This is a label, normally inside of the driver’s door pillar, but sometimes is in other locations. If it cannot be located, the owner’s manual often repeats the same information. Be careful not to merely replace what is already on the vehicle. Sometimes the last set of tires were not the proper replacement and duplicating them only duplicates the problem. This is also where a trusted professional can help. A professional can make certain you get the proper tire for your vehicle.
Tires have a series of number and letters that define their application and size. For instance P205/65R15 91H. In this example the P designates a passenger car tire. The 205 is the size in millimeters at the widest cross section of the tire. The 65 is the aspect ratio, in this case the tire sidewall is 65% as tall as it is wide. A tire that is taller or shorter than the original will result in a error in the speedometer and perhaps transmission and anti-lock brake concerns. AGCO has an online calculator to determine the effect of different size tires on speedometer performance.
The R, in the tire designation, denotes this tire is of radial construction and the 15 is the diameter of the wheel, the tire will fit on, in inches. The 91 is the load rating and corresponds to a particular load the tire can support. This load rating should always match or exceed what the vehicle maker specifies.
The H is called the speed rating, which is a bit misleading. The reason it is referred to as a speed rating is the way tires are tested. Speed rating is determined by placing the tire on a machine that spins it at very high speed. Centrifugal force acting on the tire will cause it to come apart at a certain speed. The more belting holding a tire together, the higher the speed of failure. What is important is that the replacement tires matches the rating specified for your vehicle.
Replacing tires with a lower speed rating can result in poor handling, diminished braking and traction as well as tire failure. One sign of a professional shop is they always make sure you get the proper replacement.
Unfortunately just getting the proper size and rating is still not enough. There is also the factor of age. Tires have a life span, other than just the amount of tread remaining. Many experts suggest a tire over six years of age is no longer safe to be used.
All tires have a date code indicating the week and year of manufacture. It is important to be certain the tires you are buying are not “old stock.” Sometimes tires sit in warehouses for years before being sold. Never accept a new tire that is more than 18 months old. Here’s a link with more on interpreting tire date codes.
Aside from just age, is the overall quality of the tire. This is where dealing with a reputable dealer is so important. There is a huge problem today with out of round tires being sold. Brand new tires that are simply not round.
In an effort to reduce their cost many tire makers use methods that simply do not always produce round tires. The initial symptom is a rough ride and possibly a shake or shimmy at higher speed. In time, out of round tires can cause a tremendous amount of damage to the vehicle. Leaking shocks and struts, damage to ball joints and tie rods and even damage to rack and pinion steering gears can result.
Out of round occurs more in low price tires, but several large companies have quite a problem, even in their higher priced tires.
A shake or shimmy after installing new tires indicates a problem that should always be addressed. The remedy for out of round tires is replacement. It is not unusual to see as many as four bad tires in a set. If the problem was not present before the tires were installed, it is reasonable to assume the problem is with the tire.
AGCO sells and recommends Michelin tires, installed by us. Being a diagnostic specialty shop we see most of the problem brands on a regular basis. Michelin has consistently proven itself to be a superior product that gives long lasting results.
A new set of Michelin tires mounted and balanced by the professionals at AGCO will offer the lowest overall cost, mile after mile. A great ride, no damage to the vehicle and long tire life. Michelin and AGCO is a great team. Have us check your tires today, we will be glad to provide a price quote.
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