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Bridgestone December 09 www. bus- ex. com 39 companies all have long R& D traditions. The construction of a tyre can be copied but it's a different story copying the composition of the synthetic rubbers or polymers that make up the component parts." San considers that situation is unlikely to change in a hurry, as for the past decade there has been a trend towards larger wheels and heavier loads- both of which place huge demands on the design and development of suitable tyres. Mines have often chosen to extend conveyor runs to reduce the amount of distance their earthmoving equipment has to cover. However, against this need for capital expenditure, the more conventional approach to extending tyre life has been to patch and retread. Many mines have in fact installed their own facilities for mending punctures or repairing side wall damage, although investing in machinery to undertake retreading per se remains outside the scope of anyone other than a specialist service provider. With the global recession having taken some of the heat out of the world's capacity to consume, the supply and demand ratio has largely returned to former conditions. Once again, the market is competing for share, producing downward pressure on prices. - Editorial research by Sam Howard is chosen to provide maximum cost effectiveness. The selection process is involved and needs to take in numerous operational factors. The most significant is the nature of the terrain on which the vehicles will be working, requiring a fundamental choice of cross ply or radial tyre construction. Even in mining and construction situations, radials tend to give better performance in terms of hours of working life. However, just like their urban cousins, radial side walls balloon, making them more susceptible to side wall damage when the terrain is rough. Although above ground 95 per cent of all trucks tend to be radials, stiffer side walls make cross ply the tyre most widely used underground. With operational lives varying from 2,000 to 8,000 hours, sales engineers have to get right inside the working conditions a tyre must cope with. They work closely with mine managers to make a thorough evaluation of access roads as well as agreeing on a firm specification for how the vehicle will be run. Distances, speeds and loads to be carried are all crucial if the correct selection is to be made. The world shortage of tyres opened the door to new suppliers but San is not too concerned by that. " We've seen a number of new entrants," he says, " but so far the performance of the tyres has not matched anything we produce. Eventually, they may improve but the difference is the R& D support. The main tyre manufacturing