Well having a tadpole trike (Catrike Road) and having crashed it within a
month of getting it let me chime in with some observations. The only
stability problems I've encountered are the "brake steer" effect of side to
side brakes. If one is not aware of the degree of the effect the resulst can
be an oscillating descent which causes one to stiffen up even more
compounding the problem. I've had the trike up to 58kph on relatively flat
terrain with absolutely no problems. I've had the trike up to 76kph down a
curvy descent with no problems IF I stay relaxed. The moment I begin to
tense up (ie Fear), is when instability shows up. I've had many
configurations of DF bikes, hybrids, top-end rigid MTB's and pretty good
road bikes. I've been "on the ground" with all of them too. But I have to
say for high speed cornering, DF's are best, except when you hit some junk
(gravel, RR Xings etc). At least on a trike some junk won't put you down.
And besides, at least my head isn't 7' off the ground. Falls on a DB are
usually sliding road rashers or "dive for the pavement" acrobatics. I stil
feel much safer on my bent trike

Grolsch


"Jeff Grippe" wrote in message
...
You have made some interesting observations. One of mine is that back in
the days when I rode DF's, I could easily ride without holding onto the
handlebars. I have never had a recumbent bike where I could ride without
holding on (I owned an Infinity LWB, Vision SWB, and Trek). The Trek,
which I thought I would love, was the "twitchiest" steerer. The Infinity,
which was the oldest and lowest end of the bikes I've owned was my
favorite.

I am interested in learning how Quad's would handle although I suspect
that they could also easily go up on two wheels. Its too bad I could have
a bike that became a trike on the really steep ascents.

I guess if I'm going to stick to rail trails then I could get meself a
really good two wheeled 'bent and I should be perfectly content.

Jeff
"chalo colina" wrote in message
ups.com...
32GO wrote:

Jeff and I got a bit off the topic in the TdPS. His last
post there said:

I have no problem piloting a trike in the mid to high
20's but when I go down a hill of any decent size,
I'm very quickly in the 30's and the trike does not
feel stable.

I'm often intrigued at
the conversations of 'bent bikers comparing their
impressions of long wheel-base, short wheel-base and
lowracers, and who feels safest at what speed on which
machine. Trikes are probably a bit different in that
they require almost nothing in the way of operator skill
or training at speeds up to 'casual cruising', and some
riders seem to be lulled into forgetting that as they
push the limits, trikes begin to demand some of the same
skills and heightened attention that it takes to ride a
bike fast.

I'm going to offer my observations based on lots of riding on upright
bikes and trikes. I have ridden 'bent bikes of different kinds, but I
must admit that they all felt dangerously unstable to me at any speed,
like they would dump me in a heartbeat if I even /thought/ about
letting go of the bars. I have almost no direct experience with 'bent
trikes, but I used to work with Rick Horwitz and I very briefly tried
one of his Thunderbolts.

Trikes as a rule have a natural "critical speed" that has more to do
with vehicle dynamics than it does with the rider's fear and
perceptions. Trikes can't lean, so they have a weight shift in turns.
They also have a natural steering response that is relatively
independent of speed. But as speed increases, the weight shift becomes
more sudden and eventually causes a violent response to even mild
steering inputs, up to and including high-siding the trike. Since the
effect of a harsh weight shift is to jar the rider, and this can result
in unplanned steering inputs, there comes a speed at which every trike
can be considered unstable. The lowest critical speed I have seen so
far was in a Trailmate E-Z Roll Regal adult delta trike, which tried to
buck the rider off starting at about 10mph. This was a result, I
believe, of several factors including extravagant frame flex, high C of
G, narrow track, and the misguided use of a normal bicycle fork offset
on a trike with a slack head angle. A trike will naturally become more
stable as it becomes lower, wider, stiffer, or more resistant to
steering input. That's why tadpole 'bents can be considered "sporty"
while upright deltas never are. However, while a sporty 'bent trike
might have a much higher critical speed than a senior citizen's
neighborhood trike, it still has a point beyond which it can be
considered unstable.

Bikes are different. Their front end steering characteristics cause a
natural self-stabilizing force that increases with speed. This force
causes frame, fork, and wheel flex, however, and thus can result in
shimmy problems as speeds and dynamic forces on the frame rise. But in
a bike and rider combination that does not exhibit shimmy, the ride
becomes steadier as speeds increase-- quite the opposite of what
happens with a trike. I used to have a roughly 1/2 mile downhill
averaging about 8% on my way to work, and with a mild crouch over flat
handlebars I routinely hit a measured 55mph on my upright bike--
without any unsteadiness or handling quirks whatsoever.

'Bent bikes tend to be longer, less triangulated, and smaller-wheeled
than uprights, and most of them suffer from compromised steering
geometry that does not not allow the sort of no-hands riding stability
common to uprights. Thus they will flex more (promoting shimmy) and
exhibit less self-stabilizing than a typical upright bike, and this may
contribute to a lower practical maximum operating speed. So because
'bent bikes are (generally speaking) worse than upright bikes with
regard to stability at speed, 'bent trikes are /more stable/ than
upright trikes, and this makes two- and three-wheeled 'bents comparable
to each other in their sure-footedness at high speed. In contrast,
there is really no comparison between DF bikes and upright trikes in
their handling at speed.

Chalo