(Chalo) writes:

1) True continuously variable transmission ratio, which this bike has

Some people insist we want CVT, but hydraulically driven vehicles have
always had it available and are still rather uncommon. For instance,
Hondamatic motorcycles never caught on, though their system seemed to
work as intended. I'm unconvinced that it's really as desirable as
its proponents say.

How did CVT become associated with the HPV community, when human power
seems to tolerate a wide range of RPM?

Many years ago my father drove a little DAF car which had a CVT system
which operated through pairs of opposed cones with a belt linking
them; the belt was automatically moved from one end of the cones to
the other to vary the ratio. The system was remarkably effective and
seemed quite a good thing, but as you say hasn't been widely adopted
(I think there were limitations on how much power it could
transmit). Similarly, hydraulic CVT gearboxes were around on farm
tractors when I was a boy, but the vast majority of tractors continue
to have mechanical gearboxes.

I'd like to *try* a CVT bike, particularly off road, but I suspect
losses in the system would outweigh any advantage.

2) Two-wheel drive, which this bike does not have

This is another feature that some have tried to provide, while others
wonder why. The benefits of four-wheel-drive in cars look similarly
esoteric to me, yet many people opt to pay a premium for 4WD or AWD
cars. If such a thing were available for bikes (and without glaring
shortcomings), I wonder whether there would be any noteworthy handling
benefits. I don't ride my bikes in the muck, but perhaps those who do
would appreciate 2WD?

All wheel drive on an off-road vehicle is generally a good thing,
provided that you have limited-slip differentials or the
equivalent. If one wheel spinning brings the whole vehicle to a halt
there isn't a lot of point. However, a pushbike is much lighter than
other off road vehicles. If you do get into a situation where the back
wheel just can't grip the usual solution is to put the bike on your
shoulder and walk a bit. So AWD isn't that big an issue, although it
might be useful on loose, gravelly climbs. Again, I'd be most
interested to try an AWD off-road bike, but, once again, I suspect
losses in the system would outweigh any advantage.

4) Possibly less regular maintenance and system wear

Many hydraulically powered machines work around the clock for years
between breakdowns in the hydraulic systems. (I am reminded of
various forklifts I've worked with, whose batteries always seemed to
be troublesome but whose hydraulics were seemingly invincible.)
Hydraulic systems by their nature run in a lubricant bath, and much of
the mechanical wear in them occurs to the fluid.

I am sure that not every cyclist would be willing to give up a
noticeable amount of efficiency to have a service interval measured in
years, but some certainly would if the cost were not offensive.

Now, for off-road use, that strikes me as being one *substantial*
advantage.

There's a final potential advantage to hydraulic drive which you
haven't mentioned, which is power buffering or capacitance. When you
stand up and stomp on the pedals going up hill, the power delivery to
the back wheel is anything but smooth and off-road this unsmooth power
delivery tends to break traction. With a hydro-pneumatic accumulator
you could buffer the transmission and smooth out the stomping, and
that would probably be at least as useful as AWD in marginal traction
situations.

However, the inventor of this creation claims only 90% efficiency. Am
I not right in believing that deraileur systems achieve about 93%? I
know 3% isn't much, but then bicycles are not exactly high
powered. Still, an interesting system - would definitely be fun to
play with!

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

For office use only. Please do not write or type below this line.