Studs away!

Åse Dragland

A recent SINTEF report shows that, in terms of accessibility and accident rates, there is little difference between driving with or without studded tires. Nor is there any support for the idea that studless tires wear out faster than those with studs.

The study of studded versus studless tires was carried out last winter at the request of the Gjensidige South Trøndelag insurance company. 'Studless tires in Trondheim?' is the first serious large-scale study of this topic to be conducted in Norway.

The winter of 1996/1997 was a good starting point for documenting experiences of driving with studless tires. Driving conditions in mid-Norway varied considerably, and in the course of 22 wintry weeks, a total of 306 motorists in two groups (studded and studless) reported their driving experiences. Private cars, vans and a few trucks took part in the study, which also included some public-service vehicles.

Results

The report concludes that it appears Norway is on the right track as it continues to try to reduce the percentage of studless tires in use. In general, studless tires did best on snow, while those with studs were best on icy roads. Sixteen percent of the users of studless tires reported that they had experienced some serious problems in actually getting around in the course of the winter, while the corresponding figure for users of studded tires was 12%.

Several hypotheses regarding studs were not supported by the study. For instance, there is little reason to suggest that studless tires wear out faster than those with studs. At the end of the winter, the wear on the tires used in the study was estimated to be 1.2 mm for studded tires and 1.1 mm for studless. Nor did public-service vehicles without studs seem to have problems any greater than others with studs. The evaluation suggested that there was a tendency for studless drivers of public-service vehicles to have a lower accident rate than 'studded' drivers. A third hypothesis, to the effect that it is more difficult to get around on country roads without studs because more of them tend to be covered in ice or snow, was also unsupported by the study.

Brakes, driving trains and tires

Manager of the project, Torgeir Vaa of SINTEF Civil and Environmental Engineering, Department of Traffic Engineering, reports that, ''The study also shows that certain combinations of drive trains and tire types are better than others in terms of accessibility.''

''A relatively poor combination seems to be rear-wheel drive vehicles with studless tires irrespective of the brake system. Every fourth motorist with this combination reported moderate to serious problems in getting around. As far as users of studded tires were concerned, front-wheel drive without ABS brakes was the worst combination in terms of accessibility, but the differences between different drive trains and brake systems were less noticeable here than for studless tires.''

Vaa mentions another interesting finding: motorists who drove front-wheel-drive vehicles with studless tires performed as well as drivers with front-wheel drive and studded tires. Small vans had the greatest problems in getting around, no matter what type of tire they were fitted with.

Different opinions

The two groups of users expressed quite different opinions in the study. Motorists who used studless tires were more tolerant of problems and driving performance on ice, and displayed a greater willingness to change their routes if conditions were difficult. Users of studded tires had a lower threshold of tolerance for problems involving accessibility. Many believed that they would not have survived the winter with studless tires. This group of motorists also overestimated the number of days of icy or snow-covered roads by fourteen in comparison with the 'studless' drivers.

When participants were asked to evaluate how suitable studless tires were for the stretch of road they normally used, 95% of the users of studless tires thought that this type of tire was 'good' or 'very good', while the corresponding proportion of 'studded' drivers was 72%. Of which, 28% thought that studless tires were 'poor' or 'fairly poor'.

Eighty-two percent of studless tires users supported the idea of limiting the use of studded tires, both before and after the winter. There was increasing resistance to this idea among users of studded tires: at the beginning of the season, 64% wished to limit the use of studded tires, while by the end of the winter this figure had fallen to only 46%. Ninety-four percent of the users of studless tires indicated they will buy studless tires next time, while only 43% of the other group would do so.

Tire quality

The project partners the City of Trondheim, the South-Trøndelag Division of the National Roads Administration, the Gjensidige South Trøndelag insurance company, and SINTEF also related accessibility to brand of tire. This analysis demonstrated that the various brands displayed different levels of performance. Both good-quality and poor-quality studded tires exist. The same can be said of studless tires, but different types and brands were better in this group.

According to Vaa, ''There is a lot of potential for making demands of tire quality relative to the driving performance of the vehicle. This is also a matter of sense of safety and comfort as motorists. If we feel that our tires are losing their grip in curves, driving becomes more stressful. This is especially important for drivers of public-service vehicles.''

Accidents

A total of 61 accidents of various types were reported by participants in the study. This means that every fifth driver was involved in an accident.

''These are high figures, but not surprising in light of the insurance companiesí accident statistics'', says Vaa.

''Fortunately, no injuries were involved; most of the accidents were minor collisions, cars driving off the road, or damage caused by driving into gateposts or scraping garage walls. We found no clear differences in the number of accidents between cars with or without studded tires. All the same, the large number accidents itself suggests that more attention ought to be paid to better maintenance of our roads in winter not least with a view to dealing with the growing proportion of 'studless' vehicles. A high standard on the road network would play a decisive role in limiting the extent of damage for all road users''.