"Robert Haston" wrote in message
link.net...
I just know my top cruising speed went up 10-15% from a carbon fiber
racing
upright to a dual suspended steel semi-low racer.
Actually, I didn't experience that same increase in speed when going from an
upright to a lowracer recumbent, which was surprising. I bought an M5
Lowracer last year, with the expectation of noticeable speed gains over all
my other bikes (including a Ryan Vanguard LWB). The speed gains didn't
happen. Going into a strong headwind, the M5 Lowracer was incredibly
aero-efficient. In every other situation, the M5 was about the same or
somewhat slower (that is, for a perceived output power). That's not what I
expected.
My hypothesis is that the M5 was certainly capable of being faster; but my
muscles were producing less power for a given perceived effort due to the
high BB, which I wasn't accustomed to. So, I worked just as hard, but
produced less power on the M5. I know I can produce a *lot* of power on an
upright road bike in a sprint, and can hit speeds that I never even
approached on the M5. With the obvious differences in aero advantage
between lowracers and DF's at those speeds (32 mph+), it's clear that there
was something amiss with my power production on the M5. This is what I'm
curious about with the Velokraft: Will I be able to produce power on it,
and actually take advantage of its superior aerodynamics? Or will I produce
less power than I do on my upright/DF road bike, and fail to see any
significant speed benefits? This is the question that I intend to answer
through experimentation.
Interesting gain with the tail fairing though.
Yes, very interesting. Quite significant, and without impeding the
practical use of the bike as a full fairing could. A tail fairing would be
a nice performance addition to a Velokraft; but it's a shame to ruin those
gorgeous, flowing lines. I'm already thinking about a full carbon fairing,
though, for special occasions, like fast club rides ;-) My neighbor across
the alley is a carbon fabricator (as a hobby). He produced carbon fiber
wheelchairs for some Olympic athletes a while back, and knows all about
fabbing carbon in a garage with minimal expense and tools. A blown plastic
fairing (like the WISIL guys produce) would be another option. I'm curious
to know what it's like to cruise on a recumbent at 43 mph on level ground
:-)
-=Barry=-
"B. Sanders" wrote in message
news:lLoob.49717$mZ5.311118@attbi_s54...
We all know that fully-faired recumbents own all of the human powered
speed
records. But what about unfaired recumbents vs. upright (DF) bikes?
Here's an interesting web page which cites several experiments
attempting
to
answer this question. It includes thoughtful narrative from several
riders
who offer sincere observations on the topic.
http://www.neci.nj.nec.com/homepages...a/compare.html
From the data available on Sandiway Fong's website, it looks like the
aero
efficiency (speed vs. power input) of unfaired high-racers,
quasi-lowracers
and lowracer recumbents differs only slightly from each other; but
produces
a noticeable speed advantage over DF bikes (at a given power output).
Hard
shell fully faired recumbents, as one would imagine, really start to
show
off their superior aero advantage in the upper extremes of speed
(40mph+).
Here is a chart excerpted from Mr. Fong's website (I didn't see any
copyright declarations, so I hope it's OK.)
V = velocity at a constant power output of 250 W
P = power needed to maintain constant speed of 40 km/h (~25mph)
V(mph) P(W) Bike Description
19.8 469 road bike (touring position)
21.7 362 road bike (racy position)
23.9 277 recumbent (seat hight 60 cm)
24.5 259 recumbent (seat hight 40 cm)
25.4 234 recumbent (seat hight 20 cm = low racer)
27.9 180 recumbent (seat hight 20 cm, with tail fairing)
31.6 135 recumbent (seat 20 cm, with full fairing, soft
material)
42.8 75 recumbent (very aerodynamic hard fairing)
The difference between DF/uprights and unfaired lowracers is
significant;
but the difference between unfaired and fully-faired lowracers is just
amazing. Yes, folks, according to this study, that same 75 watts of
power
that produces ~10 mph on your hybrid upright bike would have you
screaming
along at 25 mph in a fully-faired lowracer. Wow.
The difference in aero efficiency between an upright/DF racing bike and
an
unfaired high-racer recumbent is about 23% at 25mph. From my
observations
riding alongside a Bacchetta Strada in fast club rides, this seems about
right. The Bacchetta owner in our local club, Bruce, is able to pull a
paceline longer than all but the very strongest DF riders (and at higher
speeds). He's fresher and much more animated at the end of the race -
er,
I
mean ride ;-) - and continues chatting pleasantly at speeds that make
the
DF
riders (including myself) hunker down and groan with pain. I pulled a
muscle
trying to keep up with Bruce this summer on my lovely new Soulcraft road
bike. I could see that it aggravated the competitive riders when Bruce
would
cruise up from the back at 28mph and pleasantly chat with them as he
slotted
into the lead to pull for a while. Bruce gets a kick out of it, for
sure.
Once we get past the aero advantage issues, the next topic is riding
position. Open vs. closed: which is better for making power?Personally,
I'm
of the belief that a closed position is faster. I think I'm in good
company
here.
Then there's high BB vs. low BB. I've ridden them all, and I don't know
which one is faster (if any). I think once you get your legs out in
front
of you, it's all about the same. Any speed advantages probably have
more
to
do with cardiovascular advantages. Just a guess. Anybody have any good
data
on this topic?
Since I'm getting ready to buy a Velokraft carbon lowracer, I'm
revisiting
this topic. When my DF riding buddies want to know why I ride a
lowracer,
it's nice to have some data to help make my case. One look at all that
beautiful carbon weave and I don't think there will be too many
dissenting
voices.
-=Barry=-
2000 RANS Rocket
Coming Soon: 2003 Velokraft