Learn more about your tyres
Zenises understands that whilst tyres may be regarded as ‘black and round’ by many drivers, they are actually a remarkable piece of automotive engineering. But rather than bamboozle you with technical data, we’ve put together a simple guide to help you with your tyre’s performance and general care and maintenance – and therefore to help with the driving experience.
You should always remember that your tyres are the only point of contact your vehicle has with the road so you can appreciate why it is important that you select the right tyre type for the vehicle you are driving and for the purpose it is being used. It’s also the law which requires your vehicle to be fitted with the correct type and size of tyre. Moreover, it’s a good habit to regularly check all four tyres for pressure and general wear and tear – and don’t forget to check the spare tyre too.
Probably the most important advice with regard to tyre care of these is to check the tyre’s minimum tread depth. The legal limit for minimum depth of the tread on your tyres is 1.6 millimetres, across the central ¾ of the tread going around the complete circumference of the tyre.
Read on to find out more about your tyres and how to understand and care for them properly.
Tyre speed rating
All tyres are marked with a speed rating letter that corresponds to the maximum speed a vehicle can travel under conditions specified by the tyre manufacturer. These speed indexes are calculated when tyres are in a new condition. So these ratings do not apply to tyres which are damaged, under or overinflated, overloaded or repaired. And remember, just because you may have tyres which can perform at high speeds, no manufacturer would recommend driving above the legal speed limit.
The speed rating of a tyre is represented by a letter on the sidewall. For example, the “T” rating in the table below, tells us that this tyre can reach speeds of up to 190 kilometres per hour or 118mph. So when you know your tyre speed rating, you can calculate what is the maximum speed your tyre is capable of running.
Tyre load rating
The load index is a numerical code corresponding to the maximum load a tyre can carry at a speed indicated by its speed symbol under service conditions specified by the tyre manufacturer.
Radial ply tyres are now the most common tyres in use on European roads representing well over 90% of all tyres fitted today. Some radial ply tyres now have a run flat capability known as Self Supporting Run Flat (SST) tyres which are becoming more common as these tyres are now fitted as original equipment on many vehicles.
Older cross-ply (or diagonal) tyres are now very rarely seen and have effectively been replaced by radial ply tyres. Cross-ply construction tyres are more common on ‘vintage’ or ‘classic’ vehicles.
Radial ply tyres may be either steel or textile braced and are identified in the size marking by the letter “R” and often the word “Radial”.
Self Supporting Run Flat (SST) tyres are designed to provide a limited driving run on period following a puncture. These are identified by the letters “RF” in the size marking. To be categorised as a run flat tyre, the minimum distance they must achieve in a run flat condition is 80 km (50 miles) at a maximum speed of 80 km/h (50 mph) and at a minimum of 80% of their maximum load capacity.
It is essential the vehicle is equipped with a tyre pressure monitoring system to enable use of run flat tyres.
a) Non-Directional Tyres
The most common tyre pattern type is the non-directional pattern which has no special requirement with regard to orientation and position when fitting on to the vehicle. The tyre performance is not dependent on the direction of rotation.
b) Directional Tyres
A trend originally seen with the growth of high performance cars is the directional pattern which intends to provide better straight line stability. These patterns must be fitted the correct way round on the wheel and also the position on the vehicle to ensure the correct direction of rotation is achieved.
c) Asymmetric Tyres
As car performance improves, tyre design must keep pace and asymmetric patterns are becoming more common, especially on modern ‘performance’ cars. The pattern is different either side of the centre rib, and is intended to be a better balance between wet and dry handling.
Except in the case of temporary use spare tyres supplied as original equipment, it is dangerous to mix tyres of different types on the same axle. It is also advised that the same tyre type is fitted to all wheel positions.
Keep the pressure correct
Recommended tyre inflation pressures for your vehicle can be found in the vehicle handbook and/or mounted on the vehicle bodywork (for example within the door cavity or inside the fuel cap). Correct pressures are related to loads, speeds and vehicle handling and are vital for maximum safety, braking, grip and good tyre life.
Prolonged under-inflation causes excessive flexing, deterioration of the casing and rapid wear of the tread shoulders. The vehicle will also consume more fuel. Over-inflation results in an uncomfortable ride, a reduced area of contact with the road, accelerated wear on the tread centre and makes the tyre more susceptible to impact damage.
Inflation pressure should be checked at least every two weeks and only when the tyre is cold, since there is an increase in pressure when the tyre has warmed up after being run.
A reliable and accurate pressure gauge should be used.
Tyre inspection and maintenance
Examine your tyres regularly, removing stones and other objects embedded in the tread. If you see the tyre has lumps or bulges it must be examined by a tyre specialist since these could indicate internal damage. Wipe away oil or grease with a suitable diluted detergent.
Repairs to car tyres must only be carried out by a tyre specialist and in accordance with existing regulations (for example the current British Standard AU159). Permanent repairs can only be carried out following removal of the tyre from the wheel to allow a thorough inspection internally as well as externally to ensure there is no hidden damage which could result in a catastrophic failure.
To avoid such a hazard, neither externally applied plug repairs, nor liquid sealants may be considered as a permanent repair. Tyre manufacturers cannot be held responsible for problems resulting from their use.
For repairs to run flat tyres, consult the relevant tyre manufacturer.
Tyre Ageing and Servicing
The tyre industry has long recognised the consumer’s role in the regular care and maintenance of their tyres. The point at which a tyre is replaced is a decision for which the owner of the tyre is responsible. The tyre owner should consider factors to include service conditions, maintenance history, storage conditions, visual inspections, and dynamic performance. The consumer should consult a tyre service professional with any questions about tyre service life. The following information and recommendations are made to aid in assessing the point of maximum service life.