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Like international rugby forwards, tyres do most of the hard work yet

1st March 2007, Page 52
1st March 2007
Page 52
Page 53
Page 54
Page 52, 1st March 2007 — Like international rugby forwards, tyres do most of the hard work yet
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receive almost none of the glory. "kill 16.114:IV

scrums down to find out what tyres are made of and how they are tested.

Truck tyres take more abuse over their lifespan than sports referees, and nobody is more aware of this than the manufacturers.As a result they try to satisfy the numerous demands that will be made on their product, and find feasible compromises where there are conflicts of interest.

Priority is given to the need for driving safety, which includes such aspects as: power transfer to the road; braking deceleration; lateral acceleration; and general traction. Safety considerations include the tyre's connection not only to the road. but also to the truck. An exact fit to the wheel rim is vital,along with an airtight seal and resistance to shedding.

Durability is the second concern:The tyre needs to be reliable at speed. and have good blow-out and impact resistance, while the tread pattern must resist breaking up. Tyres can alter suspension characteristics, true running and driving noise comfort isn't always a paramount concern, but it can have an impact on safety by minimising driver fatigue.

Operators, however, will he more concerned with tyre economy and durability. An even pattern of wear will prolong a tyre's lifespan, and rolling resistance will affect fuel economy. The potential for regrooving or remoulding is also a consideration, as these can extend the life of the tyre.

Diverse applications

Commercial tyres have sonic of the most diverse applications in the world, and manufacturers produce ranges designed to meet the specific demands of various specialities from longdistance to urban journeys.

Cool running and minimal heat generation are prerequisites for longdistance tyres, and these are achieved through the casing construction and tyre compound. The aim is to achieve the smallest heat build-up. resul Ling in lower rolling resistance and better fuel consumption.

Long-distance journeys are more likely to use constant speeds, so the products are constructed to be more rigid, ensuring regular wear.

Steer tyres generally have ribbed patterns, while drive tyres have grippier block patterns because the drive axle requires the most traction.Trailer tyres will commonly have ribbed patterns.

Because urban trips are more likely to be stop/start, rolling resistance is not as significant. Less traction is required, as vehicles in cities are normally fitted with lowerhorsepower engines. Ribbed patterns can normally be used on all axles of urban vehicles.

Design assessments Before a tyre is commissioned to be manufactured, the designer needs to know that it can fulfil its purpose.A number of assessments are carried out, most importantly the adhesion test, which ensures that the tyre and, ultimately, the vehicle -sticks to the road: it does so by scrutinising handling,

braking and cornering. A weather test measures performance in conditions such as snow, ice and rain.

The maximum load,detennined by the load index (see table), has to comply with the EE R54 European legislation. A safety factor is built in, depending on the tyre size and its application, although the actual value is kept contidential.To ensure that the legislation is met and the manufacturer's reputation stays intact, a variety of quality-control checks are carried out before, during and after manufacture.

After a visual assessment, a drum test scrutinises the tyre's durability, heat generation, manoeuvrability, rolling resistance and vibration.A burst test checks structural strength and stability, while a plunger test checks for tyre structure and durability against impact.

Laser shearography -a method of detecting surface defects using lasers-is used to check for air pockets and the position of components, along with other internal faults. This method is very sensitive to slight alterations in surface strain due to subsurface discontinuities. Finally, the tyre undergoes a uniformity test to ensure it is, indeed, round. •

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