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