The Kowloon Motor Bus has designed some of the world's widest wheels and tyres for its three-axle double-deck buses, which it claims could improve bus stability and save fuel costs. The invention was revealed as managing director John Chan Cho-chak yesterday warned that rocketing oil prices were putting pressure on bus fares. But he said there were no plans to increase fares as this would likely be rejected by the government. Mr Chan said a US$1 increase in the price of crude oil would lead to an increase of HK$1 million in monthly operational costs. To help cut operating costs, the company planned to use its new wheel and tyre to replace the twin back wheels of the three-axle double-decker. The new wheel is 467mm wide and 91mm shorter than the twins. Its weight is 15 to 20 per cent lower than the twins, making the aggregate weight of the axle 72kg lighter. The absence of two wheels in the new design would not compromise safety and comfort, said KMB principal engineer Shum Yuet-hung. The bus company said the wider wheel and tyre will be easier on suspension systems, will reduce rolling resistance and will help prevent brakes from overheating. The lighter weight is also expected to reduce fuel costs by up to 8 per cent. 'With fuel savings up to 8 per cent, this new tyre design not only achieves conservation of natural resources, it also alleviates the pressure on operation costs,' Mr Shum said. He said the new invention also created room for a more spacious interior. The new wheels and tyres have so far been fitted only on three buses travelling on routes 7, 98A and 259D. A lengthy trial period will assess the overall performance of the new tyres before they are fitted to the rest of the company's fleet.