In addition to tread depth, drivers should also pay attention to the condition of studding. You should always check the condition of the tyres before you change them, but you should also monitor your tyres throughout the driving season, and rotate them when necessary. A recent Trafi study examined the differences in the condition of worn-out studded tyres and the associated risk factors.
It was found out in the study that drivers wait too long to acquire new studded tyres. The old studded tyres may still have reasonable tread depth, but there are no studs left or they are worn out.
For the study, we selected sets of tyres where the most worn-out tyre had a tread depth of 4–7 millimetres from among tyres left for seasonal storage at five tyre hotels. The studded tyres examined in the survey had an average tread depth of 6.1 millimetres, but serious inadequacies were detected in their studding.
In most sets of tyres, the tyre in the poorest condition had less than 60 per cent of the original studs left. About two thirds of the sets of tyres examined in the study were illegal because the differences in the number of studs were too large (more than 25 per cent).
The differences in the condition of the sets of tyres have increased. The reason for this is the popularity of cars with a front-wheel drive and the winter driving conditions in the recent years. In a car with a front-wheel drive, the rubber on the front wheels wears out faster than the studs, which means that the protrusion of the stud increases and its head can finally break off. In the freely rotating rear wheels, however, the studs wear out faster than the rubber, which means that the stud protrusion may diminish too much.
Keijo Kuikka, Special Adviser from Trafi, is of the opinion that, for reasons of traffic safety, the environment and economic considerations, all studded tyres of a vehicle should wear out at the same rate. He encourages tyre manufacturers to keep on developing the idea that the traction wheel and the freely rotating wheel would be designed differently.
The study suggests that in order to reduce the differences in the condition of tyres, motorists should rotate their studded tyres after every 3,000 kilometres if a car with a front-wheel drive is mainly used on asphalt roads. If the differences in condition get very big, the better tyres should be placed on the rear axle.
In accidents caused by passenger cars and vans during winter conditions, the tyres are usually substantially more worn out than in winter traffic in general. It seems that the loss of vehicle control often involves excessive situational speeds, the absence of electronic stability control and significantly more worn-out tyres on the rear axle.
“If the tyres are in good condition, it may help and significantly increase the margins in surprising situations. The driving situation may suddenly change, even if the driver supposes that he or she is driving at a safe speed in relation to his or her tyres and the driving conditions. The electronic stability control has improved the safety as regards keeping the car under control, but even that does not function efficiently if there is no grip,” estimates Esa Räty, road safety expert from the Finnish Crash Data Institute, who participated in the study.
More attention should be paid to the condition of tyres than people currently do. A simple tip on how to check the stud situation of your car is to keep an eye on the number of studs.
“According to the present requirements, the number of unbroken studs on any of the tyres should not deviate more than 25 per cent from the number of studs on the tyre with the highest number of studs. In addition, you must naturally also pay attention to the total number of studs. In other words, if you seem to have lost a great number of studs, it may be necessary to consider changing the tyres,” Kuikka advises.
The study Condition of studded tyres as a risk factor can be found in its entirety on the Trafi website (link to the research report). The study was conducted by J Lahti Interaction consultants.
Keijo Kuikka, Special Adviser, Trafi, tel. +358 29 534 5518, keijo.kuikka (at) trafi.fi
Finnish Crash Data Institute (OTI)
Esa Räty, Road Safety Expert, tel. +358 40 922 1365, esa.raty (at) oti.fi