There has been a lot of concern over the age of the tires we are using, even new tires.
By Denny Coughlin, Minneapolis Public School Fleet Manager from School Transportation News Magazine - March 2009
There has been a lot of concern over the age of the tires we are using, even new tires. A Dateline NBC news segment last year told of tires stored in warehouses for years but being sold as new. So how can we tell how old a tire really is? Read the DOT number.
Each tire manufactured in the United States has raised lettering located near the bead area with the letters "DOT", of the U.S. Department of Transportation, followed by a series of alphanumerics. If we can understand what these mean, it will help us understand the tire better.
The first set of, usually, two letters after DOT represents the manufacturing facility. Each tire manufacturing facility is assigned a unique set. (Click here to find the code for each facility) The next two letters indicate the tire size. These will be in code followed by the tire group or batch number. This may be referenced in a recall situation. The last set of numbers is the one we're more interested in. We cannot tell the exact date the tire was made, but we know the week and the year.
The first two numbers will range from 00 to 52 corresponding to the week in the year; the last two represent the manufacture year. For example, a tire manufactured on Feb. 5, 2009 will be represented by the characters 0509, as the date falls during the fifth full week of the year. You may see some tires with a three-digit date code indicating the week of the year, with the final digit representing the last number in the year code. These pertain to tires manufactured in the 1990's.
Each time the tire is recapped, the tire is branded with another set of numbers usually located just above the initial markings. The first four letters will start with an "R" to represent a recap, followed by the unique three letters that represent the recapping facility. The four-digit date code will again be branded into the rubber. A brand will be added each time the casing is recapped, so you can see how many times the casing has been recapped.
How old is too old? There is no simple answer. We know there are factors that deteriorate the compounds of the tire, including exposure to extreme sunlight in hot climates. Tires that are run low on air pressure cause extreme heat and can weaken or break the cords and deteriorate the rubber. Tires that are overlooked or extremely over inflated can be susceptible to damage when they run over objects or curbs.
We are fortunate in the school bus industry that we are relatively easy on tires. We do not carry extremely heavy loads, we do not run long distances at high speeds and, for most of us, we have good roads to operate on. You may think we are faced with harsh conditions, but when compared to long-haul, fully-loaded trucks or construction equipment, we operate in comparatively mild environments.
Because we must replace the front tires with new tires, we are constantly supplied with never-capped, or virgin, casings. Many of us insist on having our own casings returned with the new caps versus putting our casings into and later selecting them from a pool. We know the history of our casings, but we don't know the history of those from other fleets. While there is criteria that determines if a casing can be recapped or not, the factors of past load and heat conditions are difficult to determine.
Tires have been manufactured with a bar code attached for many years. As long as the bar code can be read, it can be tracked. Most top quality recapping shops have equipment that can look at the tire much like an x-ray to determine the structure of the tire casing. These files can be kept in storage for future reference.
There are simple things we can do to manage our tire inventory. We may look at a policy that would insist on our own casings. Due to the new (front) tires coming into our fleet, we should generally not have to recap our casings more than twice. I would look at the casings in stock, and balance the number of recaps so I don't send in a casing with multiple recaps branded when I have a virgin casing waiting for recap. Use a reputable tire recapping shop with the more up to date equipment. Visit a couple shops to learn what equipment they have and how they test and recap your casings. Spend some time with your local tire sales representative. Learn about the new tread designs and what is new in tire technology. It may save a lot of money for your fleet.