Tyres on the same axle must be of the same size and aspect ratio
You must always make sure that tyres on the same axle are of the same size and aspect ratio - your car will fail the MOT test if they're not - but the law makes an exception for temporary use spare wheels fitted in an emergency.
Temporary use spare wheels - non-standard spare/skinny spare - are increasingly being supplied as standard by car manufacturers to save space and weight. Generally these will be narrower than the standard size car tyres.
You can find details of any operating restrictions in the handbook, and the spare tyre itself should be clearly marked too. Maximum speed is usually restricted to 50mph for safety reasons.
If your car is provided with a temporary use spare wheel it is essential to check the handbook for advice before fitting the spare in place of a road-wheel.
On some cars, use of the temporary spare is restricted to ‘front only’ or ‘back only’ for safety reasons, to avoid interference with braking components or to prevent the possibility of transmission damage.
Space-saver wheels are designed for temporary use to enable the vehicle to be driven to a place of repair. There is no maximum distance but due to the speed restriction, limited tread depth (only 3mm from new) and the fact that the tyre compound is often softer to simulate the traction capabilities of a wider tyre, the distance covered before repair should not be excessive.
Aim to get the original car tyre repaired or replaced as soon as possible.
Handling will be different with a skinny spare fitted. Allow for this when driving as well as following any specific advice printed in the handbook.
If you are buying a new car don't assume that there will be a full-size spare wheel and tyre in the boot. It is increasingly common for car manufacturers to provide a non-standard or 'skinny' spare or even simply an emergency tyre sealant and compressor/inflator pack.
If carrying a full-size spare is important to you then raise it with the dealer; some offer a standard spare wheel as a cost option if the design of the boot floor can accommodate one.
Our car reviews include information on the type of spare supplied as standard.
If you are towing a caravan or trailer and get a puncture then it is generally OK for a space-saver spare to be fitted to any axle on the car. check the handbook though as there might be vehicle-specific advice.
With the skinny-spare fitted you must drive straight to a tyre specialist for a repair/replacement rather than attempt a long journey.
(21 March 2014)