I think the whole saga of the 2-axle B9s were not just miscalculation, but Volvo and Wrightbus both made some fundamental errors:
- Volvo's decision to standardise the design of the 2-axle with the 3-axle design is one rather than using the proven UK-specification design, which leave very little room at the low floor area and compromise its weight distribution. Yes it has the benefit for a bigger fuel tank and share parts with its bigger sisters, but UK-spec B9s can do the same by using 2 tanks - 1 above the front axle which is standard on the UK-spec B9, and a supplementary tank just forward the offside rear axle. This design achieve a larger tankage whilst preserve a reasonable low floor area for the bus and provides better weight distribution, and it is seen with operators like First, Yorkshire Coastliner for some years already;
- Wrightbus have been too greedy by squeezing in far too many seats to the bus. Not only the additional seats weigh more, but the legroom are actually pretty poor as well. Put that into perspective, the B9s bought by Go-Ahead Group last year - the non-London ones - only has 43 seats upstairs instead of 47 as the HK pair were originally built, and they were built to pretty much the same length as well.
In any case, based on the rumour I have heard, we will be lucky to see another Volvo in HK in the short or medium term, let alone another 2-axle B9.
I would say that still does not get away the fact that Volvo and Wrightbus have push the boat out a bit too much.
A while back I have done some back of the envelope calculation to work out the likely difference of the unladen weight of the HK-spec E400 and B9 - after the former arrives HK but before the latter comes out - based on the known weight of both types in London configuration and that of the HK-spec E400. My dead reckoning is that had Volvo and Wrightbus just upgrade a UK-spec B9 with an air-cond, and a secondary fuel tank, the weight difference between it and the E400 shall be fairly minimal - about 100-200kg in favour to the E400.
But then the B9 was changed more significantly to make it closer to the 3-axle sister, and with more seats fitted which adds weight, and not to mention the weight distribution is upset by ditching the fuel tank above the front axle in favour to a larger underfloor tank.
In my opinion, what Volvo and Wrightbus did to AVBWS1/7500 was overkilled.
