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Answers
  1. What effect does tire age have on tire durability and safety?
    This is currently a topic of significant conjecture that came to the forefront following the Ford Explorer/Firestone tire issues in the year 2000. There are no definitive studies that quantify the effects of age on tires at this time. The Department of Transportation is seeking to establish an accelerated testing procedure to evaluate the effects of tire aging. Several automobile manufacturers have included warnings in their owners’ manuals regarding tire age and have recommended replacement of tires following six years of use. The tire manufacturers have strongly disagreed with this suggestion. One tire manufacturer has stated that tires should not be in service longer than ten years. It should be noted that tire durability varies depending on operating conditions and maintenance levels. Tires should be inspected during periodic 5000 mile rotation intervals for signs that might indicate a loss of structural integrity.
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  2. How does heat affect a tire?
    Heat breaks down the sulfur-based bonds that form the molecular structure of rubber. These bonds can be gradually broken by heat accumulated over an extended period of time (Heat History). Excessive heat can destroy the molecular bonds almost instantaneously. High operating temperatures are most often caused by under inflation or overloading. Most tire debris along the highway is caused by heat-related tire failure caused by under inflation.
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  3. What causes weather checking (surface deterioration or crazing) of a tire and when is it of concern?
    Weather checking, often mistakenly called dry rot, occurs when the surface rubber loses it ability to stretch without breaking. This can result from aging, extended exposure to ultraviolet light, the presence of high levels of ozone, chemical or solvent deterioration, under inflation, heat damage, or a lack of frequent usage. Weather checking can also occur when the protective chemicals in the rubber are removed from the tire surface by frequent washing or the use of some “protective dressings.” Minor weather checking is of little concern. However excessive cracking can affect tire durability. Surface crazing that is more than 2/32 inch (1.5 mm) deep is excessive and should necessitate removal of the tire(s). Random weather checking that grows into circumferential cracks is serious. And finally deep cracking at the edge of the tread may indicate a separation and weakening of the internal structure of the tire. Tire rotation at 5000 mile intervals is recommended to monitor conditions of weather checking.
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  4. Can I replace my tires with tires that have a lower speed rating?
    No, this should never be done. Vehicle manufacturers specify a tire speed rating to match vehicle top speed as well as handling, cornering, and braking requirements. Changing to a lower speed rated tire can possibly lead to vehicle control problems. Speed rated tires are available in most price ranges so cost should not be a factor when selecting the proper tire for your vehicle.
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  5. What is plus sizing?
    Plus sizing is changing the tire size and rim diameter on a vehicle. The “plus size” refers to increasing the rim diameter. At the same time the tire size must be changed to accommodate the increased rim diameter. Care should be taken to preserve the same overall tire diameter so that computer controlled engines, transmissions, and anti-lock brake systems work properly. The load index of the replacement tire should be equal or greater than the original equipment tire specified by the vehicle manufacturer. And finally do not operate a vehicle whose handling characteristics are detrimentally affected by a change of tires or wheels.
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  6. Is the temporary spare tire safe to use?
    Yes the temporary spare tire furnished with the vehicle is safe to use when installed in accordance with the vehicle manufacturer recommendations. Consult your owners’ manual for installation instructions and vehicle operating limitations before using a temporary spare tire.
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