Quoted post said:Originally posted by Robert Canon
"Kevin Cullen" wrote
Quoted message said:Add this to the "solving imagined problems with more
technology we don't need" file.
There was a 2wd Yamaha in this year's Paris-Dakar that did
pretty well against the usual horde of larger displacement
KTMs. The system is hydraulic:
ymedc.introweb.nlwr450 2trac.shtmlOpen ↗
Dear Robert,
That's a fascinating article. Obviously, the machine's
2-wheel drive works well enough to win a major
competition.
Some of the claims, however, puzzle me.
"It feels a bit like carved skis, you can lean into corners
and the rear part of the bike takes up the same track
easily without sliding. It makes riding much more relaxed
when you don't need to counter steer."
This may refer to the two-wheel traction preventing
the need for the excessive counter-steering of a
rear-wheel power-slide, but I doubt that a powered
front wheel eliminates the normal counter-steering of
a two-wheeled contraption. It may well corner better,
but I expect that it's still counter steering through every
curve.
Another puzzling claim is this:
"The 2-Trac system makes braking safer and easier:
the bike stays well in line during braking. The rider
does not need to brake in curves, but can brake
stronger and later before cornering."
First, the braking comes from slowing down
the tires, which are unaware whether they are
struggling against an engine or a set of brake
pads. Perhaps it's simpler and easier for the rider
to use a single control (the throttle) to brake, but
it's hard to see how the braking can be "stronger."
Second, the machines stay well in line during
normal braking before curves.
Third, the best riders brake into curves, not just
before them.
Then there's this caption of an airborne machine:
"The front wheel's gyroscopic effect allows better
control when jumping."
Jumping is primarily a stunt for entertaining crowds.
(Braking, accelerating, and cornering all improve
when the tires touch the ground.)
Interesting tricks are actually possible in mid-air by
working the throttle because the bike and rider can
be forced to rotate by accelerating or decelerating
the rear wheel (a blast of throttle will cause the front
wheel to lift slightly, while chopping the throttle can
lower it slightly). But these are not gyroscopic effects,
just counter-rotations.
It's hard to see what improved stability a powered
front wheel offers in mid-air, particularly when the
aim in competition is always to keep jumps as low
and short as possible. When it leaves the ground,
the front wheel is already spinning at the best
speed for landing.
I suspect that there are advantages to this two
wheel drive system, but that they may be a trifle
exaggerated by the manufacturer and that they're
not explained as well as they could be. The link
to the engineer's interview is worth looking at,
since he seems to have a better notion of what's
going on and even contradicts some of what's
said elsewhere.
The link to the history of 2wd, for example, says:
"These systems [mechanical shaft and chain drive]
were just too heavy and also suffered from high
frictional losses that soaked up too much of the
machine’s power output."
But the link to the interview with the engineer
has a more believable explanation:
"2. It is known that the efficiency of a hydraulic
transmission is lower than of a mechanical one.
How can you justify wasting all that power?"
"Lars: Yes, that is true. But in a motorcycle application
the front wheel can just transmit very little power.
Normally 5 % and less."
The rest of the interview with the engineer stresses
that the front wheel drive functions primarily by
reducing rear-wheel spin.
Thanks for a wonderful link,
Carl Fogel
