That's right, but for the Singapore market the taller final
drive ratio and 280hp engines would be uncessary; as our transit
buses don't go above 60km/h and operates mostly on roads without
steep inclines. The short final drive ratio and smaller tyres alone
should already allow the 230hp engine to provide sufficient torque
for the terrain and loads, and up to the maximum speed of 60km/h in
Singapore.
Even though the road speed requirement in Singapore does not
exceed 60 km/h, a taller final drive ratio may provide advantages
that you wouldn't realise until you see the specific fuel
consumption curves for the relevant engines.
A shorter final drive ratio and/or smaller diameter tyres means
that the engine needs to operate at a higher speed in order to
achieve targetted road speeds in each gear. This in turn
leads to unnecessarily higher fuel consumption.
As an example of how a tall final drive ratio and a high output
engine can be beneficial, Sydney's Scania L113CRLs have a 3.80:1
final drive coupled to Scania's DSC 11 Euro 2 engine which outputs
310hp and 1315Nm. These buses have amazing off-the-line
performance despite being fitted with such a tall final drive and
return well under 40L/100km in stop-start urban traffic - better
than many of today's state-of-the-art buses. The maximum road
speed required for Sydney's city buses is 80 km/h.
As you can see, it is vitally important that bus operators
choose the correct final drive ratio for every given model of
bus. As for tyres, Australian operators prefer 11R 22.5 or
295/80R 22.5 sizes because they are far cheaper than the smaller
11/70R 22.5 and 275/70R 22.5 sizes.
