Tread depth check and legal requirements

Legal requirements for tread depth in Norway

Norway has strict legal requirements for tread depth, and the requirements differ for summer and winter tires. For summer tires the minimum legal tread depth is 1.6 mm — marked with a TWI (Tread Wear Indicator) in the groove of the tread. For winter tires the requirement is stricter: minimum 3.0 mm. Many people think the summer limit of 1.6 mm applies all year, but that is wrong — on winter tires below 3 mm you can be fined and given a ban on further driving. The police can fine on the spot and require the car to be towed home if winter tires are too thin.

Why is recommended tread depth higher than the legal requirement?

Even though the law says 1.6 mm summer and 3 mm winter, tire manufacturers, accident statistics and insurance companies recommend changing tires significantly earlier. Recommended limits are 4 mm summer and 4–5 mm winter. The reason is that wet grip falls dramatically when tread depth drops below 4 mm — wet braking distance can increase 20–30 % when you go from 4 mm to 1.6 mm. The tread is supposed to channel water away from the contact patch — without depth you get aquaplaning at much lower speeds than with new tires. On winter tires the effect is even stronger: winter tires have sipes (small slits) that "bite" into ice and snow, and these gradually disappear as the tire wears.

How do we measure tread depth?

We use precision-calibrated tread depth gauges that measure to 0.1 mm precision. We measure at several points around the tire to catch uneven wear (often more worn on the inside than the outside with wrong alignment), and log the figures in your customer record. Tire hotel customers get this measurement free at every seasonal change. If one tire has significantly less tread than the others, it is often a sign of underlying problems such as alignment, poor balancing or an unnoticed puncture.

Consequences of too little tread

Too little tread causes concrete safety problems: longer braking distance — especially on wet surfaces (the difference between 8 mm and 1.6 mm can be 5–10 metres when braking from 80 km/h on wet), increased risk of aquaplaning at much lower speeds than with new tires, poorer cornering grip and reduced lateral stability, and increased risk of puncture because the inner steel of the tire comes closer to the surface. In addition all of these are illegal driving below legal requirements, with risk of fines and insurance consequences in an accident.

Simple home test: 1 NOK coin test

You can do a rough check at home: stick a 1 NOK coin into the tread groove with the "Norge" lettering pointing inward. If the entire "Norge" is visible, you have less than 4 mm left and should plan for new tires. If you can't see it, you have more than 4 mm. This is a rough method — for an exact figure come by and we measure for free. Check-up visits are recommended at every seasonal change, before long holiday trips, and if you notice worse grip or longer braking distance than usual.

Book online easily or call us on 41 17 32 24.