Hankook is supplying a city bus tyre in the size 315/60 R 22.5 optimised for electromotive use. The SmartCity AU04+ has low rolling resistance which helps to ease the strain on the energy storage units of electric-powered urban buses. On account of the increased vehicle weight resulting from the battery weight, the tyre not only has a stable carcass but also an increased load capacity of 154/148J (156/152F) which corresponds to a weight of 8 tonnes per axle. The standard load bearing capacity is usually 7 tonnes per axle for this size.
During development of the new bus tyre, special attention was paid to a high traction and braking performance, particularly on wet road surfaces.
Klaus Krause, head of the European Research and Development Centre, said: “Unlike conventional combustion engines, an electric motor is able to deliver the full torque immediately. This means the vehicle and the tyres respond faster to speed or the changing road conditions. Consequently more demands are made on tyres for electric-powered vehicles. The high grip level avoids irregular tyre wear without having to do without optimum mileage.”
The high mileage is guaranteed by the optimised zigzag grooves which ensure higher block rigidity due to their modified layout, among other things. The constant starting and stopping in city traffic puts a heavy and irregular load on bus tyres.
“For this reason we have adapted the shoulder width and design for the SmartCity AU04+ to the increased requirements, thus guaranteeing more even wear. The improved molecular structure of the new tread compound makes the tyre much more heat-resistant and is a further contributing factor to a longer service life,” said Krause .
The SmartCity AU04+ also has a further reinforced sidewall. This protects the tyre from damage following the often unavoidable contact with the curb in city traffic.
“The reinforced sidewall is particularly important for the protection of electric bus tyres, since they accelerate much more quickly on account of the system and also build up a more aggressive contact to curbstones,” added Krause.
