It looks like the fella behind this CVT hydraulic bike is trying to raise some capital by selling
off his prototype:
cgi.ebay.comeBayISAPI.dllOpen ↗
powerengine.compowerengine.comOpen ↗
It seems like a cool artifact, if not particularly practical.
I know this particular bike has come up for discussion before, with a certain amount of pooh-poohing
of the general concept. Since this thing surfaced again, I've been reflecting on what hypothetical
advantages a hydraulically driven bike could have over a chain driven bike, which might offset the
drawbacks of what is almost certainly a heavier, lossier, and more expensive system than chain
drive. So far I've come up with:
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?
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?
3) Integral braking, which the inventor's website mentions, but which does not appear to be
incorporated into this bike
I think that having a bike's drive and braking functions integrated into the same apparatus is the
most desirable potential feature of a hydraulic drivetrain. Check valves could be adjusted to match
available maximum braking torque to the load, and the force required to close the braking valves
would be miniscule compared to that required to actuate normal rim or hub brakes.
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.
5) No intrinsic configuration constraints
This seems most relevant to suspension bikes, where chain drive and suspension components compete
for space and exert forces upon each other, and to recumbents, where the rider's behind often
interrupts the straight line between drive sprocket and driven sprocket. But the hydraulic
"driveline" is just a pair of hoses, and can be fitted around (or through) other mechanisms. It
could be routed under the cargo bed of a carrier bike, for instance, or within a frame tube to a
drive wheel far removed from the crank. Even a crank is not a given; it could just as well be
treadles or something else yet.
The possibilities outrun my ability to imagine good uses for them-- so much about the bikes we know
is just corollary to the chain drive, that it's difficult to imagine what a "normal" bike would be
like in the absence of one. The high wheeler is what you get when you assume that a bike's cranks
will drive its axle directly, and the diamond frame with derailleurs is what you get when you assume
the use of a chain drive. If you don't assume either of those things, then what?
I suppose the answer to that will have to await another feasible alternative, if there is one.
Chalo Colina