Most car owners think that the best way to measure how safe their tires are is by using a tread depth gauge (or Abe Lincoln’s head on a penny), but maybe you should be using a calendar instead. This issue was taken up in a paper delivered to the Human Factors and Ergonomics Society in 2006.
The study worked with 225 participants, gathered from student and non-student pools, and only four percent indicated that tire age was a contributing factor in tire failures. NHTSA recommends that tires should be checked after five years and then annually thereafter but also states at the site www.safercar.gov that “even an inspection performed by an expert may not always reveal the extent of tire deterioration.”
First a distinction needs to made between dry rot in tires, which was identified to a higher degree (10 percent) in the study when participants were asked to describe the “types of problems that you believe could occur…” with a car’s tires. The authors make the distinction that dry rot or cracking may “result from tire aging” but that an unsafe tire due to age may not be visible to the naked eye, while of course cracking and dry rotting are.
How do you establish the age of your tires? The sidewall of your tire carries an identification number that begins with “DOT”. The last four digits of the number represent the week and the year in which the tire was manufactured. Depending on the manufacture date, the numbers may be on either side of the tire.
Here’s some background information from NHTSA that might put your mind at ease. In 2004 tire life was estimated to be 44,700 miles accumulated over 3.6 years, so maybe you’re like the majority of people who wear their tires out before they have a chance to degrade due to age. This also suggests, however, that one of the first things you should do when purchasing a used car, especially from a private owner, is to determine the age of the tires. This would be a case of what you don’t know being able to hurt you.
NHSTA estimates that about 400 fatalities a year are caused by tire failures of all sorts. In terms of aging the most susceptible tire populations would exist in warmer climates and areas where weather conditions are coastal or have high exposure to sunlight.
It's interesting that the study was conducted by the Department of Psychology at North Carolina State University and presented to the HFES. The society's seeks “ to promote the discovery and exchange of knowledge concerning the characteristics of human beings that are applicable to the design of systems and devices of all kinds.” This issue of unperceivable danger in an aging tire seems to be all about perception and focus. In their conclusions the authors suggest a number of warning strategies which if adopted could increase consumer awareness.