For the past couple of days we've discussed various issues surrounding car tires, first here and then here. Today something else came to my attention - a danger of which I'd not previously been aware.
It seems that tires can be safely stored and used for several years after their date of manufacture. However, after that 'safe period', the rubber and other materials used in their construction can deteriorate, leading to unsafe conditions such as tread separation, etc. In 2008, ABC News reported:
Despite years of study that point to a mounting toll of deaths and injuries attributed to aged tires, the National Highway Traffic Safety Administration (NHTSA) has refused to issue a warning to consumers on the issue.
"We are extraordinarily disappointed by the fact that they are saying, 'We know this is a safety problem,' but they won't tell consumers," said auto safety expert Sean Kane.
As tires age, they can dry out and become brittle, leading to potential catastrophic tire tread separations. Kane's private research firm Safety Research & Strategies has so far tracked 167 vehicle crashes it attributes to aged tires, with 192 injuries and 139 fatalities. "An old tire is like a ticking time bomb in many ways," said Kane. "You don't know what's going on inside it. That's what makes it so dangerous."
NHTSA has known about the risks of aged tires for years, and in a 2007 report to Congress the agency acknowledged that "tire aging is a serious safety issue." NHTSA's report noted that insurance statistics from a number of states showed 84 percent of tire-related claims were for "tires over 6 years old." NHTSA refused a request, however, from Ford Motor Co. to impose a six-year shelf life on tires, based on the company's independent research.
"We have rejected that notion," said NHTSA spokesperson Ray Tyson, pointing to the fact that some tire and auto manufacturers have issued their own shelf life recommendations for tires, which he said is "sufficient." Bridgestone/Firestone, Michelin and other tire manufacturers have issued bulletins recommending a 10-year shelf life for tires. Auto companies, such as Ford, Chrysler and Toyota, have issued 6-year recommendations.
There's more at the link.
Intrigued, I asked my contact at a local dealer about this. To my surprise, he was hesitant to answer, at least in the hearing of other managers. Eventually we managed to get a moment of privacy, and he informed me that age does, indeed, appear to be a factor in tire safety: but tire wholesalers and retailers typically don't want to acknowledge it, because they have older tires in stock, and they wouldn't be able to sell them if the problem were more widely known. As it is, they can and do sell them, and if some of them exhibit problems they'll replace them under warranty. That's cheaper than trashing all of them, because some older tires (particularly those fitted to vehicles that don't drive very often, or very far, or very fast) might not give any trouble.
I was pretty upset to hear that tire suppliers may be risking the lives of their customers in this way, and asked him how one could identify the age of a tire. He pointed me to a very useful British Web site, Carbibles.com, which includes a section labeled 'Wheel & Tyre Bible' (yes, Britain spells 'tire' with a 'y' instead of an 'i'). This is packed with information about any and all aspects of tires and their use. Here's what it says about tire dates.
DOT Codes and the 6-year shelf life
As part of the DOT code (G in the tyre marking above), there is a tyre manufacture date stamped on the sidewall. Oddly this code is sometimes only one one sidewall so you might need to get under your car and look at the inward-facing side of the tyre. Take a look at yours - there will be a three- or four-digit code. This code denotes when the tyre was manufactured, and as a rule-of-thumb, you should never use tyres more than 6 years old. The rubber in tyres degrades over time, irrespective of whether the tyre is being used or not. When you get a tyre change, if you can, see if the tyre place will allow you to inspect the new tyres first. It's not uncommon for these shops to have stuff in stock which is more than 6 years old. The tyre might look brand new, but it will delaminate or have some other failure within weeks of being put on a vehicle.
Reading the code. The code is pretty simple. The three-digit code was used for tyres manufactured before 2000. So for example 1 7 6 means it was manufactured in the 17th week of 6th year of the decade. In this case it means 1986. For tyres manufactured in the 90's, the same code holds true but there is a little triangle after the DOT code. So for this example, a tyre manufactured in the 17th week of 1996 would have the code 176∆ .
After 2000, the code was switched to a 4-digit code. Same rules apply, so for example 3 0 0 3 means the tyre was manufactured in the 30th week of 2003.
If the tyre has a 3-digit code, do not buy it. It will be too old.
There's much more at the link. I really think that entire Web page is essential reading, for safety reasons; so please take the time to click over there and learn more about the subject. Some of its information may not apply to the USA or the country in which you're reading it, but you can use that information as a starting point to find out where your national markings and/or regulations differ. (For US readers, see this page at the Tire Rack Web site for further information about US age codes.)
Anyway, there's something else to think about when checking your existing tires, or planning to purchase new ones - and it's certainly a strong argument against buying older used tires!