Replacing the hub gear on a Giant Lafree Twist

A while ago I asked for advice on replacing the 3 speed hub gear on a
Giant lafree twist with a 5 or 7 speed version. I took the plunge and
ordered a 7 speed Shimano Nexus hub from my local Giant dealer. It took
them ages to get the bits -they couldn't source the twist grip, so I
got it myself from St John's St Cycles. Then they found that when
rebuilding the wheel, that the spokes were thicker even than mountain
bike spokes, and they had to order in tandem spokes instead. Eventually
it was done and I've now had chance to try it out a few times.
I kept the original 16 tooth sprocket, so I've effectively got one gear
lower, one higher and two gears between the original three. Most
noticeably, the highest gear enables me to pedal faster on the flat or
downhill -I can now now continue to get some push at up to 22mph,
whereas it used to run out at about 17mph.
The middle gears are also useful -I often found the motor cutting in
and out frequently at, say, 10mph in 2nd, but if I changed to 3rd it
was too much of a push . I now have another gear in between and it
makes transitions much smoother.
I wasn't sure if the lower gear was any use at all to start with, as by
the time I'd run out of power in 2nd, changing to 1st just meant the
motor cut out, so I wasn't getting anything extra. However, I've learnt
to adjust my cadence and I've now found I can get up a steep gradient I
used to give up on.
Overall -a worthwhile improvement. The cost £160. Was it worth it?
-depends on whether you can afford £160. For me, it means a more
enjoyable ride, and the confidence to go a bit further, as I've now got
a more useable manual bike if the battery runs out on me.

As an aside, does anyone understand the mechanism whereby the bike
detects when the motor is required? I'm assuming it's to do with the
tension in the chain rather than the speed, but I find it's action
erratic and wondered if it could be adjusted. For example, if I'm
pedalling uphill in say 3rd, and running out of puff, I change down to
2nd -often there will be a delay of about 20 seconds before the motor
cuts in again. On occasion it doesn't cut in at all and I'm left
struggling on a motorless bike. I've tried pressing down harder on the
pedals , but what usually does it, is to change down a gear briefly
until the motor restarts and then change quickly back to the gear I
want, when it will continue running. Any idea why?

wrote:
I can now now continue to get some push at up to 22mph,
whereas it used to run out at about 17mph.

I'm certainly no expert on electric bikes but I think you may want to
keep quiet about the extra speed. I understand the current regulations
only allow power to be provided up to 15mph. Have a look he
http://www.whycycle.co.uk/electric.htm. Anything faster is no longer
classed as a bicycle. Still, sounds like a useful upgrade.

Mike

Sorry -what I wrote was a little misleading - what I meant was that
having the higher gear means I can go faster downhill without the
motor. The motor still cuts out somwhere between 10 and 16mph , but
before I couldn't push on the pedals to get extra speed downhill -my
legs were just flailing at 17mph. The extra gear means I can continue
to apply leg power up to about 22mph.