Tyres: summer tyres & winter tyres – driving licence theory

Studded winter tyres.

Studded winter tyres.

Different types of tyres

  • Summer tyres are the type of tyres you must use when winter road conditions are not prevailing.
  • Winter tyres are marked “MS” (Mud and Snow) and come in 2 varieties:
    • Studded tyres = good grip on snow and icy surfaces, but causes a lot of wear on the roads.
    • Friction tyres = good grip on snow, slightly less on ice, less wear on the roads.
  • Year-round tyres are not suitable in Sweden, considering the long and icy winters.

The main differences between summer and winter tyres are the tread pattern and the rubber compound. If summer tyres are used in the winter, the more sensitive rubber can become hard and therefore have worse properties.

Tread depth

Tyres Tread depth
New tyres 8–9 mm
Worse wet grip 3–4 mm
Minimum permitted on summer tyres 1.6 mm
Minimum permitted on winter tyres 3 mm

When it is obligatory to use winter tyres, and when it is prohibited

  • The law on winter tyres in winter road conditions 1 December–31 March.
  • It is prohibited to have studded tyres 16 April–30 September unless winter conditions are prevailing or expected.

Winter road conditions exist when there is snow, ice, slush or frost on some part of the road.

Clarification about winter tyres

It is May 4 and winter road conditions. Am I allowed to use studded tyres?
– Yes, since it is winter road conditions.

It is 1 July and no winter road conditions can be expected. Am I allowed to use non-studded winter tyres?
– Yes, only studded tyres are forbidden. However, consider that the performance of the winter tyre will be degraded in hot weather. If your car is not safe to drive, it is forbidden.

It is 10 December and autumn weather (no winter road conditions). Am I allowed to use summer tyres?
– Yes, the dates forcing you to have winter tyres only apply during winter road conditions. However, consider that the performance of the winter tyre will be degraded in hot weather. If your car is not safe to drive, it is forbidden.

Air pressure in the tyres

Correct air pressure is important.

Correct air pressure is important.

Example of air pressure values in relation to the instruction book’s recommended values:

  • 30% below – not good; higher fuel consumption and the tyres’ lifespan can be halved.
  • The exact values written in the instruction book – good.
  • 10–15% over – the best; lower fuel consumption and the potential to double the tyres’ lifespan, whilst at the same time there is no negative impact on traffic safety.
  • More than 20% over – not good; no gains whilst at the same time the handling begins to deteriorate with excessive pressure. Wear on the tyres increases.

The risk that the tyre will explode is in principle non-existent if you pump it up at a petrol station. It would require much higher pressure than what a normal compressor can provide.

Spare tyre in the event of a puncture

  • A regular spare tyre is exactly the same type of tyre that the car normally has. You are allowed to drive with this just as with a regular tyre. However, it is often best to repair the old wheel and put it back, as a brand new tyre on one side can worsen the car’s handling.
  • A temporary spare is a narrower tyre version that is only suitable for bringing the car into a shop. The car’s instruction manual contains instructions regarding maximum speed, maximum distance and lifting pressure for the temporary spare.

If the regular or temporary spare is a summer tyre and the others are studded tyres, you are permitted to drive with the tyre until the studded tyre has been repaired.

Tyre fault

  • Incorrect wheel alignment causes the car to pull to one side if you hold the steering wheel loosely on a straight road. This leads to uneven wear on the tyres. It can be caused by the tyres bumping into something.
  • Incorrect balancing (steering wheel shakes) leads to the steering wheel vibrating occasionally. This leads to increased tyre wear.

Tyre-related facts

  • It is prohibited to combine summer tyres and winter tyres. Nor is it permitted to combine studded winter tyres with non-studded winter tyres.
    • Exception: If you get a puncture on a car with winter tyres fitted, you may use a summer spare tyre until the winter tyre has been fixed.
  • Changing only one tyre leads to a deterioration of the car’s handling. You should therefore change both tyres on the same axle. It is best to change all tyres at the same time.
  • When changing a tyre, you should re-tighten the wheel bolts after several tens of kilometres of driving in order to reduce the risk of them loosening.
  • If the car has studded tyres, the trailer must also have studded tyres in winter road conditions. However, the opposite is not true; i.e., a car does not necessarily have to have studded tyres just because the trailer does.
  • Summer tyres with snow chains may be used as an alternative to winter tyres.
  • Higher speeds wear more on the tyres than lower.
  • Smooth driving is better for the tyres.

Tyre glossary

  • Retreaded tyres are used tyres that have been fitted with new treads. Cheaper, but with potentially worse properties than entirely new tyres.
  • The tread is the patterned part of the tyre in contact with and worn by the road.
  • Friction is the resistance between two objects sliding against one another. Ice skates on ice = low friction. Eraser on paper = high friction. The friction between the tyres and the road must be high in order to achieve the best grip.
  • Tread wear indicators are small pieces of rubber which sit inside the grooves of the tyres. When the tyre tread has worn down so much that they are on a level with the tread wear indicators, the tyre should be changed as soon as possible.

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