Tyre Tips
Tyres are the only parts of the car which are in contact with the road. Safety in acceleration, braking, steering and cornering all depend on a relatively small area of road contact. It is therefore of paramount importance that tyres should be maintained in good condition at all times and that when the time comes to change them the correct replacements are fitted.
The original tyres for a car are determined by joint consultation between the car and tyre manufacturers and take into account all aspects of operation. It is recommended that changes in tyre size or type should not be undertaken without seeking advice from the car or tyre manufacturers, as the effect on car handling, safety and clearances must be taken into account.
In some other European countries it is illegal to use replacements which differ in certain respects (e.g. size, load, and speed rating) from the tyre fitted originally by the vehicle manufacturer.
Quick links:
Types of tyre
Radial ply tyres are now the most common tyres in use on British roads representing more than 90%. Some radial ply tyres now have a run flat capability known as Self Supporting Run Flat (SST) tyres which are becoming more common particularly when fitted as an original equipment. Older diagonal (cross-) ply tyres are now very rarely seen and have effectively been replaced by radial ply tyres.
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 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 50 miles (80 km) at a maximum speed of 50 mph (80 km/h) 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.
Top of page
Do not mix tyre types
Except in the case of temporary use spare tyres supplied as original equipment, it is illegal in the United Kingdom and 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.
Top of page
Keep the pressure correct
Recommended tyre inflation pressures for your vehicle can be found in the vehicle handbook and/or on a placard mounted on the vehicle. In the absence of either of these consult the tyre manufacturer. 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.
Top of page
Inspection and maintenance
Examine your tyres regularly, removing stones and other objects embedded in the tread. If 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.
Top of page
Watch your tread
Tyre treads are designed to give good grip on wet roads, but in general wet grip decreases as tyre tread pattern wears down or as the depth of water increases. Motorists should take this into consideration and reduce speed when it is wet.
The legal minimum tread depth in the UK is 1.6mm throughout a continuous band comprising the central three-quarters of the breadth of tread and round the entire outer circumference of the tyre. However tyre wet grip deteriorates more rapidly in the second half of its tread life and wet stopping distances can dramatically lengthen. It is therefore advisable consideration is given to replacing tyres well before they reach the legal minimum.
Top of page
Caravans and car trailers
Caravan and car trailer tyres may be radial or on older vehicles diagonal (cross-) ply construction irrespective of what type is fitted to the towing vehicle. Both tyres on a caravan or trailer axle must be of the same size and type. Caravan and trailer tyres often require higher inflation pressures than are required for the same tyres on a car. It is essential correct tyre pressures be determined and maintained.
When towing in the absence of any recommendation in the vehicle handbook, increase the towing vehicle’s rear tyre pressures by 4 to 6 psi (0.3 to 0.4 bar) to improve stability of the complete unit.
Top of page
Temporary use spare tyres
Temporary use spare tyres are frequently a different size to the standard road tyres. Severe operating restrictions apply. Failure to observe the advice given in the vehicle handbook and/or on the tyre sidewall could have very serious consequences.
Do not exceed 50 mph when using a temporary use spare tyre and observe the minimum inflation pressure.
Top of page
Valves
A new valve should be fitted when replacing tubeless tyres. When checking or adjusting inflation pressure, always ensure the valve is not leaking. A new cap of the sealing type should be fitted.
Top of page
Tyre repairs
Repairs to car tyres must only be carried out by a tyre specialist and in accordance with 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 self supporting run flat tyres, consult the relevant tyre manufacturer.
Top of page
Wheels and rims
It is essential the wheel size is an approved fitment for the tyre and vehicle concerned. Tyres must not be used on damaged, distorted or modified wheels since this could result in tyre damage, deflation and possible loss of control of the vehicle.
Top of page
Removal and fitting of tyres
These operations should only be entrusted to a trained tyre specialist who has the necessary equipment and expertise. Inexpert fitting can result in injury and damage to tyres and wheels. Wheels should be balanced after tyres are fitted or replaced.
Top of page
Tyre ‘Load’ and ‘Speed’ markings
With few exceptions, tyres new or retreaded are required by law to carry indications of the tyre’s load carrying and speed capabilities e.g. 205/55R16 91V. These are moulded on the sidewall as a service description comprising a Load Index for load carrying capacity and a Speed Symbol for speed capability. It is strongly recommended to always fit tyres that have a speed capability and load index at least equal to or higher than those originally specified by the vehicle manufacturer.
Top of page
General information
Driving over pot-holes, kerbs, speed humps etc even at low speed can result in the weakening or fracture of the tyre’s structure. It is dangerous to re-inflate a tyre which has been run flat or seriously under inflated and such tyres should be removed for complete examination by a tyre specialist.
Tyre manufacturers cannot be held responsible for problems arising from modifications to their products, or the use of sealants which they have not approved.
Top of page
Tyre service life and ageing
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.
Tyres are designed and built to provide many thousands of miles of excellent service. For maximum benefit, tyres must be maintained properly to avoid tyre damage and abuse that may result in tyre disablement. The service life of a tyre is a cumulative function of the storage, stowing, rotation and service conditions, which a tyre is subjected to throughout its life (load, speed, inflation pressure, road hazard injury, etc.). Since service conditions vary widely, accurately predicting the service life of any specific tyre in chronological time is not possible.
Tyres should be removed from service for numerous reasons, including tread worn down to minimum depth, damage or abuse (punctures, cuts, impacts, cracks, bulges, under inflation, overloading, etc). For these reasons tyres, including spares, must be inspected routinely, i.e., at least once a month. This routine inspection should occur whether or not the vehicle is equipped with a tyre pressure monitoring system (TPMS). Regular inspection becomes particularly important the longer a tyre is kept in service. If tyre damage is suspected or found, It is recommended that the consumer has the tyre inspected by a tyre service professional. Consumers should use this consultation to determine if the tyres can continue in service. It is recommended that spare tyres be inspected at the same time.
Consumers are strongly encouraged to be aware of their tyres’ visual condition, such as cracking/crazing of the tread/sidewall rubber. Also, they should be alert for any change in dynamic performance such as increased air loss, noise or vibration. Such changes could be an indicator that one or more of the tyres should be immediately removed from service to prevent a tyre disablement. Also, the consumer should be the first to recognise a severe in-service impact to a tyre and to ensure that the tyre is inspected immediately thereafter.
Tyre storage, stowage and rotation are also important to the service life of the tyre.
There is no known technical data that supports a specific tyre age for removal from service. However, in the interests of safety it is recommended that all tyres (including spare tyres) that were manufactured more than ten (10) years previous be replaced with new tyres, even when tyres appear to be usable from their external appearance and if the tread depth may have not reached the minimum wear out depth. Vehicle manufacturers may recommend a different chronological age at which a tyre should be replaced based on their understanding of the specific vehicle application; it is recommended that any such instruction be followed. Consumers should note that most tyres would have to be removed for tread wear-out or other causes before any proscribed removal period. A stated removal period in no way reduces the consumer’s responsibility to replace tyres as needed.
The chronological age of any tyre can be found on the tyre sidewall by examining the characters following the symbol "DOT".
For tyres manufactured after the year 1999, the last four numbers identify the date of manufacture of the tyre to the nearest week. The first two of these four numbers identify the week of manufacture (which range from "01" to "52"). The last two numbers identify the year of manufacture (e.g., a tyre with the information "DOT XXXXXX2703” was manufactured in the 27th week of 2003).
For tyres manufactured prior to the year 2000, three numbers instead of four indicate the date of manufacture. Also, during the early 1990s, a triangle was added (▲) to the end of the character string to distinguish a tyre built in the 1990s from previous decades (e.g., a tyre with the information "DOT XXXXXX274 ▲was manufactured in the 27th week of 1994).
Top of page
Directional and asymmetric patterned tyres
Some tyres have patterns where their direction of rotation is important to achieve their full performance. These are known as ‘Directional’ pattern tyres and the direction of rotation is marked on the tyre’s sidewall.
Additionally some tyres have patterns which are different on the inner half of the tread than compared to the outer half. These tyres, known as ‘asymmetric’, have their sidewalls marked ‘outside’ and/or ‘inside’ or similar wording.
It is important with both these tyre types to observe the fitting markings on the tyre sidewall.
Information taken from www.tyresafe.org
2B Pitreavie Business Park, Queensferry Road, Dunfermline, Fife, KY11 8UT
Maintained by Catch PR | Net A Tyre Ltd 2010 © Buy Tyres Online from The Leading Online Tyre Retailer, UK
Company Registration: Net A Tyre Limited 179 Rumblingwell Dunfermline Fife KY12 9AR
Company No: SC318624