That is true. I agree that the gearbox changes gears according
to acceleration also, with drags occuring for slow acceleration,
and for impatient drivers. But assuming that the driver applies the
same pressure on the accelerator for the same gearbox with
different programmings, the behavior of the gear changes will
differ also. Take for example the Leyland Olympian 3-Axle vs the
Volvo counterpart, both are fairly similar buses with the same
ZF4HP500 gearbox.
Applying the same pressure on both buses, the LO would change from
1st to 2nd fairly quickly and with less dragging. The VO would on
the other hand drag its 1st gear slightly to increase its momentum
before switching to 2nd at a significantly higher rpm.
There are of course reasons why the tuning differs for both types.
The LO has a 'loose' 1st gear because it can deal with it. I've
come across VOs with the same kind of tuning and the results can be
horrible with vibrations as the bus loses momentum when the lock-up
occurs too quickly, in certain cases, the lock-up kicks in another
2 times before the VO lumbers off into 2nd gear. An LO with a ZF
tuned like the VO is more likely make passengers satisfied with the
higher rate of increase in momentum, but such tuning is not so much
required.
Hence, both acceleration and rpm factors in on the gearbox's
behavior. Oh, and I'm no technician also, the above is just based
on what I observe as a passenger. If the information I gave is
confusing/misleading or utterly wrong, then I'm really sorry.
