Wrench Tips #33: Old Tires Suck!
There are a lot of goofy, semi-nonsensical numbers in the tire business, but if you're a tire-scrounging cheapass like me, this one is pretty important. Somewhere on every sidewall is a four-digit number from a changeable plate in the tire mould. The letters can mean whatever you want (but they really correspond to the factory the tire came from), but the numbers are a manufacturing date code. Naturally, like everything else in the tire business the code is unnecessarily obtuse. The second two numbers are, as expected, the year, but the first two are the week. Wha?
Yeah, whatever. Knowing the year is good enough.
You see, tires get shittier when they get older, so knowing roughly how old your tires are can be really important. How exactly old tires get shitty is chemistry, so I don't understand it, but like most chemistry, it depends on exposure to sunlight, temperature, and random variables you'll never understand.
When skunky old tires go bad, its not always immediately obvious. Old tires can still have nearly as much grip as they did new, but their limit behavior is what tends to fall apart. Breakaway gets sudden and unpredictable, and regaining grip gets harder. This makes it really easy to accidentally lock up your 6-year old Michelin Pilot Sport Cups coming into the corkscrew and flat spot them down to the cord, forcing you to drive 300 miles home listening to the deafening spastic drumbeat of square tires only to finally have one pop in downtown LA at midnight. It can also make 3 year old, $20 Dunlop Direzza Star Specs trickier to control, making all your LeMons teammates cry like little babies.
Three years is an unusually short lifespan for a tire, but environmental factors may have been partially to blame there. While those 3-year old tires lived a life of sun and fun parked outdoors in toxic LA, I recently checked a set of Yokohama Advan Neova AD07 Lotus Elise tires (there's a unique Lotus spec) that spent half their life in Tire Rack's warehouse and the other half in a dark garage, and they still work fine.
So, after checking the date code, give the tread a close look and a tap with your fingernail. Skunky tires will start to look a little shiny, and the tread surface will have a hard, plasticky surface. You can also roll down your windows and listen to the sound of them rolling across the pavement at low speeds and listen for the scratchy sound of Big Wheel tires. If your tires sound like a Big Wheel's, your car will probably handle like one.