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Technical Review

08/05/2019
Hankook

Mid-size and long (from 7 to 12 metres) electric buses are now a reality on many urban and suburban networks in Italy: there are at least two hundred in circulation, 51 of them in Turin alone. Unlike diesel engines, electric engines immediately generate torque that is very close to maximum, with the consequent problems of grip. Moreover, the battery pack increases the tare of a 12 m bus by about 2.5 tons compared to an equivalent internal combustion engine. Carcass structure and tread pattern must, therefore, take these differences into consideration; the first manufacturer to do this was Hankook with its Smart City AU04+ dedicated to urban electric buses. It comes in sizes 315/60 R22,5 (load index 154/158J, tread depth 13 mm, on the EU tyre label C for fuel efficiency, B for grip and 73 dB for noise level) and 275/70 R22.5 (152/149F, 19 mm, classifications D, B and 67 dB). The structure shows optimised shoulder width, which gives better handling and stability, while the sidewall has no tabs and is reinforced to prevent cuts and chips due to holes and contact with the kerb when pulling in to the bus stop. The tread is zig-zag with stiff blocks to improve traction in the presence of high torques and, therefore, faster acceleration.

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