On Fri, 01 Apr 2016 17:16:40 +0100, Dave Plowman (News) wrote:

In article ,
Roger Mills wrote:
Indeed they are. The rate of acceleration is dependent on gearbox
*output* torque - not on engine torque.

And the two are directly related.

Why is it impossible to see this? A gearbox simply multiplies the torque
of the engine.

I think we can all accept that as "A Given". However, for a given road
speed where the selected gearbox ratio matches the peak engine power
revs, you will gain a modest increase in torque applied to the driven
wheels compared to a ratio selected to allow the engine to run at peak
torque revs.

If we assume the theoretical case of a perfect stepless gearbox which
can automatically adjust the ratio to hold the engine to its peak torque
rpm as the road speed increases, you'll find that the resulting
acceleration will be less than one configured to hold the engine to its
peak power output rpm (it will operate at a larger reduction ratio in
this case which increases the torque applied to the road wheels compared
to the ratio range used to keep the engine operating at its maximum
torque rpm).

In the case of a manual gearbox, we approximate this mode of operation
by choosing max power rpm as the next change up point rather than the
lower peak torque rpm point.

--
Johnny B Good