B
B. Sanders
Guest
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/sandiway/bike/festina/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)
20.7 362 road bike (racy position)
21.9 277 recumbent (seat hight 60 cm)
22.5 259 recumbent (seat hight 40 cm)
23.4 234 recumbent (seat hight 20 cm = low racer)
24.9 180 recumbent (seat hight 20 cm, with tail fairing)
25.6 135 recumbent (seat 20 cm, with full fairing, soft material)
26.8 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
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/sandiway/bike/festina/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)
20.7 362 road bike (racy position)
21.9 277 recumbent (seat hight 60 cm)
22.5 259 recumbent (seat hight 40 cm)
23.4 234 recumbent (seat hight 20 cm = low racer)
24.9 180 recumbent (seat hight 20 cm, with tail fairing)
25.6 135 recumbent (seat 20 cm, with full fairing, soft material)
26.8 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