A study commissioned by traffic safety watchdog Trafi finds that some 60-70 percent of studded tyre sets are sub-standard.
Trafi reported discrepancy in the number of embedded studs on different tyres in the same set, and in the studs' rate of wear per millimetre.
The figures corroborate an Aalto University study from last year, and were found by inspecting the tyres stored in so-called "tyre hotels" or storage garages.
As the facilities accrue a fee for storage, the tyres held there tend to be brand varieties (Michelin, Nokian, Continental, etc.) and of higher than average quality.
Wear and tear leads to deaths
Cars and vans with especially worn tyres are most likely to be involved in wintertime traffic accidents. Three specific factors linked with crashes are too high speeds, lack of stability control systems and well below average back-axle winter tyres.
Trafi says that the findings of the tyre report published in early October "are worrying enough to warrant widespread investigation."
The quality of the studs themselves was found to be variable. In most of the sets of four tyres examined, less than 60 percent of the studs were intact. Fewer than every fourth set had more than 80 percent of its studs, and 13 percent of all tyre sets were found to have no undamaged studs at all.
Discrepancies in the depth of the grooves in studded tyres were also found to be alarming, with about half exhibiting at least 2 mm differences.
Winter season traffic accidents have, however, decreased drastically since the early 2000s, with fewer than 30 accidents per year leading to loss of life in recent years.