First and foremost, excuse my poor English. Next, my experience with recumbents is limited to a RWD homemade recumbent I've bought this winter and tracked about 3.5 thousand kilometers this season, including a
400-km brevet with about 3k of climbing... (compare to my
last year result on DF, and that is chinese carbon rigid niner running SuperMoto 2.35 tires) but I think I've pinpointed the REAL reason what makes recumbents less efficient when it comes to power output.
I'm a natural born maximizer, so my next 'homebuild' will be pretty damn well researched... I've sunk quite a few hours of feverish brainstorming and article-reading into it.
Warning, lots of 'further reading' via hyperlinks!
1.
Pedaling angle:
Optimal angle
seems to be about 105. More or less seem to diminish your ability to output power considerably... unfortunately, this position is not very aerodynamic, so some sacrifices will have to be made - like being able to 'lay flat' on flats and sit/stand up nearly vertically - on hills, where aerodynamics is not that important. It is possible on a DF bike, and Cruzbike cockpit configuration seems to support that as well (but it may be possible with RWD recumbent too).
2.
Power transfer:
I think this is
HUGE, and I've yet to see anyone mention that, so here it goes:
For every action, there is an equal and opposite reaction. Unlike gravity, that 'gives back as much as it takes', pushing against your own back (as in 'lower back, heh') tissues and seat padding introduces huge losses into the system, much moreso than 'frame stiffness losses' and the like, I bet my life on that.
Imagine taping large slabs of fatty meat wrapped in seat padding to your feet and trying to pedal! You may actually try to do it, but I don't think that would just be a waste of good food to prove that 'water is wet'. After all, road shoes with carbon-soles are supremely stiff for a reason.
When you counteract this force by pulling on the bars instead of pushing against the seat, you eliminate much of the inefficiency, because our bones and tendons are much more efficient when it comes to tension, unlike our tissues when it comes to compression, as in 'pulling on a rope' vs 'pushing against a sponge'. No contest.
Of course, some mechanical losses would STILL occur as compared to gravity that is 100% efficient, but this is a sacrifice we have to make.
3. Anatomy and cardiovascular system limits.
Since we are not evolved to apply power 'legs upwards', our cardiovascular system may not be up to the task. It is subject to personal variation, of course, and as this
very insightful article states, some are affected more than others - as I, myself, found out to much of my chagrin. (Hence, I'll have to do with something akin to Silvio geometry, not Vendetta - less incline, less seat to BB vertical distance).
Anyway, our major veins and arteries that power the legs in the lower back region must suffer some impingement during pushing against your seat as well, hence the problem is further exacerbated (again, subject to variation in personal physiology and seat geometry).
Imagine this as you push down the gas pedal on your car, you pinch down a gas fuel hose that goes right beneath it, effectively limiting your fuel supply to the engine when you need it most! (At least when it comes to the
internal iliac veins and arteries).
The dreaded 'numb toes' syndrome that strikes when you push the hardest could be indication of that too.
Effectiveness of 'bridging' must come from removing above mentioned impingements, but power transfer losses still apply, not to mention physical and mental effort of maintaining this position and adaption of ineffective (see 1.) nearly 180 degrees pedaling angle.
Again, this problem is avoided by a cockpit design that allows pulling on the bars instead of pushing against the seat, FWD or RWD notwithstanding (but, of course, FWD is more efficient when it comes to losses in drivetrain).
There is an alternative, of course - counteracting the push by pulling against the contact pedals, but we run full force into the limits of our physiology again, as described in these two articles:
The Myth of the Upstroke
Which Muscles are Really Used During the Pedal Stroke?
First one is especially insightful, because I fully experienced the symptoms described as I tried to 'pedal circles':
• Lower-back pain
• Tightness and pain in the hip
• Loss of power and efficiency
• A feeling of floating or disengagement on one or both legs
• In extreme cases – impingement in the iliac artery!
The 3rd comes directly from the latter - and since our arteries already experiencing impingement (because you can NEVER fully counteract our strongest and largest muscles with much smaller ones no matter how you train them, not to mention the weight we put on them while we lay down in our seat - that may be a problem in itself for heavier riders like I am, for instance) - this solution might be worse than the problem.
Conclusion:
Pulling on the bars instead of pushing against your back or trying to pedal circles avoids all these problems, and most widespread 'hamster' and 'avatar' bars are simply useless for that, and superman bars are only marginally more useful. And far as I understand, none of RWD cockpits are designed for that purpose.
Cruzbike cockpit with road bars (or bullhorns) you can pull against is optimal. My guess that you can emulate that cockpit with RWD design too, but it might interfere with steering, as well as add further complication to drivetrain and some loss of efficiency.
Unfortunately, I'm dirt poor and lack necessary equipment for proper measurement and testing, so I would not mind some R&D money Jim promised sent my way
.
Anyway, to be serious, I really hope that my efforts and research would be useful, and if they do, I'd love to have Silvio frameset sent my way someday, because I sure as hell will never be able to afford it myself.
So far I'll have to manage with a one that is made from steel, lack suspension and likely weight about 40 pounds, but I need something for ultra-cycling that does not kill my butt, back and hands, and 'Cruzbike' seems to be a PERFECT design for the job.
EDIT:
I've spoke with a friend of mine, who happens to be an avid cyclist (not recumbent variety, though) MD and surgeon, so he is quite familiar with anatomy to put it mildly.
He said that, unless you already have some sort of pathology, impingement of veins from recument position is unlikely, impingement of arteries is even less likely, so disregard that.
What I meant as impingement of external veins is already known as 'recument butt', so disregard that too (but still, less pressure - more blood - more power, our glutes are largest muscles in the body).
Everything else stands, though.
As for real possibility of impingement,
sciatic nerve is at real risk here, and it can produce similar negative results.
bike parked at Woodinville Commons
