GOOD TYRES ARE VITALTyres are the vehicle's only point of contact with the road. The actual area of contact between the car and the road through the tyres is small, roughly equivalent to four size eight men's shoes. Bald tyres - 'slicks' - may be fine for a race car on a dry track, but no good at all for road vehicles on a wet road surface. Tyres treads are designed to pump water from the road surface and provide maximum grip. By the time the tread is worn down to the legal limit they will be unable to perform this task efficiently and MUST be replaced. RoSPA recommends that worn tyres are replaced with an equivalent new unit well before the legal minimum tread limit of 1.6mm is reached - ideally as soon as they reach 2.5mm.The Right Tyres for the Vehicle Motor vehicle manufacturers choose the type, make, size, profile, load carrying capacities and speed ratings to match their vehicles, adjusting the tyre pressures to give the optimum grip, ride and handling characteristics. Only change the type of tyres on your vehicle on expert advice. Tyre MaintenanceTread Depth Pay special attention to the amount of tread remaining on your tyres, and measure them regularly (details of minimum legal tread depths is given below). Always replace tyres before they reach the legal limit.Pressures The vehicle’s handbook provides guidance about how to look after your tyres. It will also contain information about vehicle loading and the required adjustments to tyre pressures which should be followed for safety. Tyre pressures should always be checked and corrected (if necessary) when they are cold. It is vital that tyre pressures are maintained at the levels recommended by the manufacturer to ensure maximum tyre life, the best ride and handling characteristics. Over or under-inflating tyres is likely to seriously impair their performance and may prejudice the safe use of the vehicle. Over-inflation increases overall tyre diameter, decreases the amount of tread in contact with the road, decreases sidewall flexibility and affects road-adhesion. Under-inflation decreases overall tyre diameter, increases sidewall flexion, generates higher tyre operating temperatures and difficult vehicle handling characteristics. Under extreme conditions running an under-inflated tyre may cause premature tyre failure. Both over and under-inflation adversely affect tyre life.Cleaning Treads Keep tyre treads clean of stones and other foreign bodies, and check regularly for damage to the tread and side-walls. It is vitally important that any damage is checked out by a tyre expert and any necessary repairs or replacements are carried out immediately.Tyre valves Check tyre valves carefully. Ensure the caps are in place and that there is no evidence of cracking or damage to the valve stem.Part-Worn TyresWhat are part-worn tyres?Part-worn' tyres are those which have been used previously - in other words they are 'second-hand'. Most part-worn tyres are imported, mainly coming from continental Europe.What are the potential problems with part-worn tyres? Part-worn tyres are usually sold with about 50 per cent of their original tread remaining and may have several thousand miles more motoring in them. However, despite their remaining tread, it must be appreciated part-worn tyres are nevertheless USED TYRES. As such their purchase and use should be treated with a degree of healthy scepticism. In many cases, such tyres will be perfectly sound. However, it is possible that they have been bumped up and down kerbs and over other obstacles. They may have been run over or under-inflated, and may have sustained irreparable and invisible damage to their structure. The cost of part-worn tyres reflects their second-hand state and this no doubt contributes to their attraction to motorists. The purchase and use of part-worn, instead of new, tyres may enable some owners to afford to keep their vehicles on the road. The tyre industry continues to express concern about the sale and use of part worn tyres. However, it is important to consider the issue objectively and make a reasoned judgement about the real risks of using such tyres. RoSPA's advice, like that of Trading Standards Officers, is 'let the buyer beware'. Whether the purchase of part-worn tyres is a good economic proposition or not, there can be little argument that a tyre which is only half worn but is in all other aspects sound, is likely to be safer than a tyre worn to the legal limit.Remoulded TyresWhat is a remould tyre?A remould tyre is made from an old tyre. Old tyres which are not sound should never be used as components for remould tyres. The essential building block for a remould tyre is a used tyre whose tread is worn-out but whose carcass (basic structure) is sound. Preparation for remoulding involves stripping away the tread of the worn-out tyre. The final part of the process moulds a new tread onto the old carcass using a new rubber compound.What problems are there with remould tyres? In the majority of cases remould tyres perform satisfactorily provided the manufacturer’s guidance about maximum vehicle loadings and maximum speeds is followed. Overloading, sustained high speeds, and under or over-inflation all contribute to increased tyre wear and/or premature failure.The Tyre LawTyre Pressures Tyre pressures should be maintained at or within a very close tolerance of the recommended pressures.Tyre Tread Depth and Damage When tyres become worn or damaged they must be replaced. There must, by law, be at least 1.6mm of tread depth across the centre 3/4 of the width of the tread throughout the entire circumference of the tyre. There must be no damage to the tyre body - sidewalls or tread, no bulges or cuts.Tyre Types It is illegal to mix tyres of a different construction (cross-ply; bias belted or radial) on the same axle. Cross-ply and bias-belted tyres are seldom used on production cars, and are not widely available in the UK. Cross-ply and radial tyres should never be mixed on the same vehicle. Where a mix is necessary, radial tyres MUST only ever be used on the rear axle and cross-ply tyres on the front. This mix of tyres will produce 'over steer' whereas the opposite will produce 'under-steer'. (Over-steer refers to the car turning more tightly into a corner than it is steered; under-steer indicates that the vehicle turns at less of an angle than it is steered). Of the two conditions, over-steer is generally accepted to be easier to control.