Tyre Ageing

All tyres undergo an "ageing process" due to exposure to the environment even if they have never been used or have only been used occasionally.

This phenomenon is caused by a number of factors including:

• the process of aftercuring, whereby the tyre continues to culcanise very slowly. This is caused by factors such as light, heat and movement and makes the tyre become stiffer and more brittle.
• oxidation involving oxygen and ozone from the atomosphere causing hardening of the rubber and reduced elasticity
• plasticisers drifting from the tread area to other parts of the tyre, resulting in increased hardness.

Tyre ageing can be minimised by proper storage in a cool, dry environment, away from direct sunlight and away from electric motors (such as air conditioning units) or other sources of ozone.

Interestingly, tyres, which are infrequently used or not used at all, age and crack quicker than tyres, which are in regular use. For this reason tyre manufactureres tend to recommend including the spare tyre in any tyre rotation process. Spare tyres, which are old should be used with caution. If in doubt, get the tyre checked by a tyre expert.

Caravan tyres or tyres on other vehicles that are parked for long periods are particularly subject to ageing and owners of these vehicles are generally advised to jack the weight off the tyres and cover them so that they are not exposed to sunlight.

How long before tyres become too old?

This is rather like asking "how long can a piece of food be kept before it goes off?" and therefore it is something on which the tyre manufacturers have some difficulty in agreeing. No expert can definitively say how long a tyre will last as a tyre's life depends on many factors such as the type of rubber compounds used, temperature, usage, humidity etc.

However, Bridgestone's website points out that many tyre companies, including Bridgestone, offer manufacturing warranties on tyres for 5 years from the date of manufacture, which has resulted in many vehicle manufacturers advising against the use of tyres that are more than six years old.

The British tyre industry has not been able to agree on a definitive statement relating to tyre ageing. As a result of this the National Tyre Distributors Association is understood to be preparing a members' advice document for release in early 2008, which is said to be based on a similar leaflet produced by the German tyre dealers association (BRV)

The BRV's advice on the subject is, in fact, based on a joint statement dating back to 2001 and prepared in conjunction with Bridgestone, Continental, Dunlop, Goodyear, Michelin and Pirelli, which advises dealers to make sure tyres are not sold, which have a production date that lies more than 5 years in the past.

In terms of tyres already fitted to vehicles the BRV advises a maximum age of 10 years for car tyres and 6 years for tyres fitted to caravans, trailers of other vehicles likely to be standing around for long periods.

How do I check the age of my tyres?

All tyres are marked with a serial tyre identification number. The last three digits (for tyres made before 2000) or the last four digits (for tyres manufactured after 2000) denote the week and year of manufacture. For example, a tyre carrying the number 3506 denotes a tyre manufactured in the 35th week of 2006.