Tyres: summer tyres & winter tyres – driving licence theory

Different types of tyres

• Summer tyres.
• Winter tyres, which are available in these variants:
  • Studded tyres: Best on icy surfaces, but cause a lot of wear on the roads. Older cars without anti-skid systems should have studded tyres.
  • Friction tyres: As good as studded tyres, except on ice. Friction tyres roll more quietly and wear less on the roads. Choose friction tyres if you have a car with an anti-skid system and often experience mild winters where you live.

The pattern and rubber compound differ between summer tyres and winter tyres. Driving with friction tyres in the summer can cause dangerous situations, because the rubber in the tyres becomes too soft.

There are tyres that are marketed as year-round tyres. These are not suitable for use in Sweden given the large differences between summer and winter.

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 legal requirement for winter tyres in winter road conditions: 1 December–31 March.
• It is prohibited to have studded tyres 16 April–30 September unless the prevailing or expected road conditions are wintry.

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

Studded tyres and human health

The studs rip up particles that are hazardous to human health. This is the most important reason for the ban on studded tyres between 16 April–30 September unless the prevailing or expected road conditions are wintry.

On some stretches of road in big cities, the air quality is so bad that studded tyres are banned altogether. This ban is marked with a road sign and applies even during the winter.

Tyre-related facts

• Correct air pressure is important for safety and the lifespan of the tyres. See the car’s user manual and information from the tyre manufacturer.
• It is prohibited to combine summer tyres and winter tyres. It is also prohibited to combine studded winter tyres and non-studded winter tyres.
  • Exception: If you get a puncture on a car fitted with winter tyres, 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.
• After 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.
• Summer tyres with snow chains may be used as an alternative to winter tyres.
• Tyres are subjected to greater wear at higher speeds.
• Smooth driving is better for the tyres.
• The tread is the patterned part of the tyre that is in contact with, and is worn by, the road surface.
• Retreaded tyres are used tyres that have been fitted with new treads. These are cheaper, but may potentially have worse properties than brand new tyres
• 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 it is level with the tread wear indicators, the tyre should be changed as soon as possible.

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 causes the steering wheel to vibrate occasionally. This leads to increased tyre wear.

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 having a brand new tyre on one side can impair the car’s handling.
• A temporary spare is a narrower tyre version that is only suitable for use in order to get the car to a workshop. The car’s user manual contains instructions regarding the maximum speed, maximum distance and the air pressure for the temporary spare.

Studded tyres on a trailer

If the car has studded tyres, then the trailer must also have studded tyres in winter road conditions. If the trailer has studded tyres, then the car does not need to have them.

This is to avoid the risk of jack-knifing, which occurs when the car has better grip than the trailer during braking. The result will be that the trailer skids to the side in an uncontrolled manner.

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