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Worn tyres a common safety risk on Finnish roads

Tyres turned in at recycling centres in Finland are on average six years old, the upper limit of manufacturers' suggested product lifetime.

Dot-merkintä autonrenkaassa.
The date of tyre manufacture can be seen from the four digit DOT code. The first two digits are the week of manufacture, the last two the year. The "3715" in this photograph shows that the tyre was manufactured during week 37 of 2015. Image: Yle Uutisgrafiikka / Derrick Frilund

While there are minimum standards for the condition of tyres on motor vehicles in Finland, there are no restrictions on their age.

Manufacturers suggest that tyres be used for no more than six years. Additionally, they recommend that motorists do not use tyres older than 10 years. Tyres over five years old, even if unused, should not be sold as new.

However many cars on the road are likely to be running on tyres beyond their best-before date, according to Risto Tuominen, CEO of the recycling company Suomen Rengaskierrätys.

"Three years ago we checked and found that the tyres coming in for recycling were on average 6.2 years old. That was the average. Some of the tyres were really old, up to 22 years old. There was no real difference between summer and winter tyres," Tuominen told Yle.

Age as important as tread

Jyrki Vuorinen, Professor of Materials Science at the Tampere University of Technology, says 5-6 years is the longest period he had used the same tyres, and he compares them to fresh baked goods.

Modern tyres, he explains, are made of a complex mix of components, some of which improve for a while, but all of which weaken with age. Professor Vuorinen says that the age of a tyre is every bit as important as how much tread it has. As tyres age, they harden, creating less friction, and so less grip on the road surface.

"As a tyre's performance gradually worsens, the driver compensates. But, what happens when an elk steps out in front of you when you're doing 100km/h? A car handles in a completely different manner on new tyres. Nobody expects a t-shirt to last forever. It deteriorates during the cycle of wash and wear. Why would a tyre be any different?" Vuorinen asks.

Proper storage important

With the need for both summer and winter tyres, one set is always in storage for months at a time.

The lifespan of tyres is not only affected by use. Other factors such as exposure to UV radiation, ozone and heat have an impact.

"If properly stored out of direct light, six months is no problem. However, your furnace room is too hot. Heat tends to ruin tyres more than does the cold," Professor Vuorinen advises.

Vuorinen adds that putting older tyres on your car is not the best idea, even if they are unused.

"Who wants to drive on ten year-old technology? Not many people would want to use a ten year-old computer," he notes.

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