Road bike vs. recumbent comparison

[Osiris]

Anyway, I don't grasp all the implications myself, but you must admit that you can, at least, *spread* the load over your legs and arms by doing either bike rocking or boom swinging

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If I agreed with that, we wouldn't be having this argument. I've tried several times to explain to you why I don't agree, but you don't seem to understand the explanation, and I'm not sure what else I can say that would further clarify things.

And it can also be pretty big in effect and be a distinct advantage! (I really need to model how much this effect differs between an MBB bent like Vendetta and DF though sometime... should not be too hard in CAD)

I've already done the calculations in CAD. Here's what I came up with based on the following measurements:

Distance from handlebar to pivot point (directly over the front axle) = 21"
Distance from hip joint to pedal (with crank at 90 degrees) = 34"
Distance from center of pedal to center of boom = 6"

This gives me all the measurements needed to create a CAD model and calculate the amount of pedal movement resulting from moving the handlebars.
Starting with the handlebars in their perfectly straight position, I moved them 2" to the left.
This shortens the distance from the right pedal to my hip joint by 0.75".
Put another way, moving the handlebar left 2" will only move the right pedal 0.75" forward.

As you can see, moving the handlebars accomplishes very little, and I'm not sure I would even move the handlebar as far as 2" when riding. It takes only a small amount of movement at the handlebars to cause a very significant directional change. I would need to do some experiments to see how far I can swing the handlebars while riding the bent in a controlled manner. That will have to wait for the weekend.

You can either have them shortened for a modest fee at any decent bike shop, or buy some BMX race cranks, they go as short as about 120 and very cheap to boot (ebay). Most of them are square taper and not hollow-forged though (forget carbon), but what you lose in weight (as - gain ... and not much due to shortening) you gain in aero tenfold if you ask me... does your Vendetta still need external cups for fixing the chainstays though?
Some of them do use external cups - much pricier though. I've bought a set of 140mm BMX race myself AND had 170mm MTB cranks shortened by about 22mm as well.

I see. I didn't look into having them shortened, but I do know that the several bike shops I took it to said there were no cranksets under 165mm that would fit this bent. At least none that were listed in any of their parts catalogs.

 

[super slim]

http://www.bikesmithdesign.com/Short_Cranks/apex.html
$219 for a Sram Apex crankset shortened to 137.5 to 158 mm.

 

[Balor]

http://www.bikesmithdesign.com/Short_Cranks/apex.html
$219 for a Sram Apex crankset shortened to 137.5 to 158 mm.

Pretty decent cost given the labour costs.

 

[Balor]

If I agreed with that, we wouldn't be having this argument. I've tried several times to explain to you why I don't agree, but you don't seem to understand the explanation, and I'm not sure what else I can say that would further clarify things.

Well, like I said, I don't really grasp the intricacies of having your arms and legs provide torque AND pedal movement in tandem, but manipulating pedal displacement seems like a plausible explanation. That's how I do it on DF, anyway, and you at least agreed that fixing a leg and swinging the bike into it and just extending your legs are two very distinctive biomechanical modes.

I would need to do some experiments to see how far I can swing the handlebars while riding the bent in a controlled manner.

I think there was a video where Jim demonstrated 'boom swinging' somewhere and did more than that...

 

[Osiris]

Well, like I said, I don't really grasp the intricacies of having your arms and legs provide torque AND pedal movement in tandem, but manipulating pedal displacement seems like a plausible explanation. That's how I do it on DF, anyway, and you at least agreed that fixing a leg and swinging the bike into it and just extending your legs are two very distinctive biomechanical modes.

Yes, and that was actually one of the theories I was kicking around when trying to understand what might account for the claim of increased power when moving the handlebars. But I realized after watching Jim's video that that wasn't what people were describing.

I think there was a video where Jim demonstrated 'boom swinging' somewhere and did more than that...

It's right here:

The part of interest to us starts at about 1:13. It's hard to estimate the amount of handlebar movement with the bike wobbling around that much, but if you look closely at how far the boom deviates from the center line of the frame, it's actually quite small.

 

[Balor]

Well, yea. I think I do it father than that when climbing sitting upright... I also can lean the bike WAY to the side, lean in the oppose direction and use resulting camber torque to negotiate turns with much more grip - not unlike how motocross riders do it. It is also way fun!

After seeing the video once again I think you should account for not only for swinging the bike into your leg, but swinging it OUT of your leg on backstroke. When you think about it, this is almost exactly what eccentric rotor cranks Ed (and I, if only I could install it on my bent...) do.

 

[Osiris]

Well, yea. I think I do it father than that when climbing sitting upright... I also can lean the bike WAY to the side, lean in the oppose direction and use resulting camber torque to negotiate turns with much more grip - not unlike how motocross riders do it. It is also way fun!

I could do that on my CA2 when sitting fully upright, which made it incredibly easy to make tight turns at very slow speeds. Your custom bent has a very different geometry from my Vendetta (or any Cruzbike for that matter), so I have no idea what sort of forces are in play when pedaling and steering your recumbent.

After seeing the video once again I think you should account for not only for swinging the bike into your leg, but swinging it OUT of your leg on backstroke. When you think about it, this is almost exactly what eccentric rotor cranks Ed (and I, if only I could install it on my bent...) do.

Things get much more complicated when you add other factors like leaning the bike on it's axis, or imagining what might be happening on the return stroke, which only underscores the problem of testing Jim's claim empirically. If you get a negative result, there's nothing preventing someone from objecting that you got a negative result, not because the theory doesn't work, but because you weren't performing the technique correctly. That's why I still think testing it on a trainer as in trplay's setup is the best way to get to the bottom of it, though even that clearly takes a lot of practice to eliminate the erratic power readings he got.

 

[Balor]

I could do that on my CA2 when sitting fully upright, which made it incredibly easy to make tight turns at very slow speeds. Your custom bent has a very different geometry from my Vendetta (or any Cruzbike for that matter), so I have no idea what sort of forces are in play when pedaling and steering your recumbent.

Nothing special really, just zero flop with plenty of trail (but something you very rarely see on a bicycle). Might have more 'pedal induced torque' due to straight angle (though it also results in better 'boom swinging' potential, actually - easy to see that with 0 deg stering angle you'll get zero pedal displacement no matter how much you twist your steering), but my boom is only 30cm, hence totally manageable and less steering inertia as well, plus 70% of weight over front tire which is a mixed blessing given my weight - I should have went with 120 instead of 130cm wheelbase.

Things get much more complicated when you add other factors like leaning the bike on it's axis, or imagining what might be happening on the return stroke, which only underscores the problem of testing Jim's claim empirically. If you get a negative result, there's nothing preventing someone from objecting that you got a negative result, not because the theory doesn't work, but because you weren't performing the technique correctly. That's why I still think testing it on a trainer as in trplay's setup is the best way to get to the bottom of it, though even that clearly takes a lot of practice to eliminate the erratic power readings he got.

Yea. That's why I reserve judgement and my preliminary leaning is that it *must* work in principle (because, like I said, you manipulate pedal displacement by your upper body), but I'm not sure how significant effect is. It is undoubtedly less than on DF (where the 'pivot angle' is also 90 deg).

 

[Osiris]

Nothing special really, just zero flop with plenty of trail (but something you very rarely see on a bicycle). Might have more 'pedal induced torque' due to straight angle (though it also results in better 'boom swinging' potential, actually - easy to see that with 0 deg stering angle you'll get zero pedal displacement no matter how much you twist your steering), but my boom is only 30cm, hence totally manageable and less steering inertia as well, plus 70% of weight over front tire which is a mixed blessing given my weight - I should have went with 120 instead of 130cm wheelbase.

That's why I gave the dimensions I was working with when I created my CAD model. It occurred to me at the time that not only was my Vendetta likely to have very different dimensions from your custom built recumbent, but that it would also be different from other Cruzbikes, depending on the particular model and individual setup for each rider (boom length, BB height, etc). What all this means is that even if we assume for the sake of argument that Jim's theory that swinging the handlebars assists pedaling, how effective it would prove to be would depend on the bent's dimensions.

Yea. That's why I reserve judgement and my preliminary leaning is that it *must* work in principle (because, like I said, you manipulate pedal displacement by your upper body), but I'm not sure how significant effect is. It is undoubtedly less than on DF (where the 'pivot angle' is also 90 deg).

Absolutely. The other factor that isn't mentioned is that leaning a DF doesn't necessarily result in a steering input. By contrast, it's impossible to move the handlebars on a Cruzbike in the way Jim suggests without causing the bent to change direction, and the greater the amount of handlebar movement, the greater the directional changes. This is why I've never been able do a decent sprint on my Vendetta like I can on my fixed boom recumbents. Given the huge amount of power going into the pedals and the rapid change in cadence as I shift through the gears, there's just no way I can can perfectly adjust for the effects of pedal steer with the right amount of handlebar pulling to prevent a dangerous front end weave.

 

[Balor]

Absolutely. The other factor that isn't mentioned is that leaning a DF doesn't necessarily result in a steering input. By contrast, it's impossible to move the handlebars on a Cruzbike in the way Jim suggests without causing the bent to change direction, and the greater the amount of handlebar movement, the greater the directional changes. This is why I've never been able do a decent sprint on my Vendetta like I can on my fixed boom recumbents. Given the huge amount of power going into the pedals and the rapid change in cadence as I shift through the gears, there's just no way I can can perfectly adjust for the effects of pedal steer with the right amount of handlebar pulling to prevent a dangerous front end weave.

Actually, camber thrust (as evidence by some 'lean steer' bikes) can and does provide ability to change direction, in fact moto racers are known to steer OUT of the turn during hard cornering because they need to 'detune too much camber thrust with negative slip angle' (c) Foale.
On bicycles the effect is not THAT drastic, but you can negotiate much tigher turning circles using much less handlebar turn angle this way compared to a car (or a trike). Camber thrust is relatively obscure phenomena, but camber torque is well-known in fat bike world as 'self-steer' up the cambered surfaces.

To negate this effect you'll need to steer out of the lean as you rock your bike.
On Vendetta this is, basically, vice versa.

P.S. I get some camber torque myself when I ride up and down 'ruts' in asphalt made by trucks. This is due to lots of trail and huge weight over the front wheel, multiplying the effect nearly by two (those effects are due to friction, more traction - more friction)

 

[Osiris]

So this morning I finally got the timing down perfectly. While climbing an uphill segment at a modest speed, I managed find just the right pace that allowed me to synchronize the pulling of the handlebars with each pedals stroke. It did cause the bent to zig-zag as in previous attempts, but this time there were no other trail users to contend with. At any rate, the important thing was not to keep the bent going in a perfectly straight line, but to keep my pedaling consistent so that I could obtain reliable power readings. Can you guess the results Balor?

 

[Balor]

What did I say again about you being coy?
I have no idea, of course. I do not have a power meter yet hence any experiments I'll do will be inconclusive, but I am inclined to think that benefit can go a few ways, depending on your anaerobic capacity, VOmax and upper body strength/agility:
Higher max power.
Ability to maintain same level of power longer that otherwise.
All of the above
None of the above, because you may add some power, but fail to contibute enough to overcome inevitable frictional losses (trail and camber torque related).

 

[trplay]

I would guess if he needed the trail vacated because of his excessive wobble he didn't use the correct technique. It would be better if he found someone who does understand the technique that could demonstrate this to him before he tries any more experimentation. Sounds like Osiris took a wrong turn to the Ball Room dancing class and ended up at a mud wrestling event.

 

[Osiris]

What did I say again about you being coy?
I have no idea, of course. I do not have a power meter yet hence any experiments I'll do will be inconclusive, but I am inclined to think that benefit can go a few ways, depending on your anaerobic capacity, VOmax and upper body strength/agility:
Higher max power.

Well, you're going to need more than just a power meter; you're also going to need a Cruzbike. That is after all what we're talking about here. Your custom built bent has an entirely different geometry, so what's true about your bent isn't necessarily true of Cruzbikes.

Ability to maintain same level of power longer that otherwise.
All of the above
None of the above, because you may add some power, but fail to contibute enough to overcome inevitable frictional losses (trail and camber torque related).

Well, that pretty much exhausts all the possibilities. Before I get into the results, let me just comment on a couple of things we've touched on previously. The first thing to note is that in order for the technique to even have a change of producing measurable results, you have to be able to move the handlebars far enough to make a significant change in the distance from your hip joint to the pedal (HP). In theory, the more you can pull the pedal toward you, the more power your upper body contributes. My previous calculations based on 2" of handlebar movement showed only a 3/4" change in HP. That's a very small amount. You could achieve the same effect just by flexing your calves. In reality, I found that the amount of handlebar movement would be significantly less than 2" in order to prevent huge steering inputs. How much less is impossible to say exactly without some device to measure the amount of change to the boom angle, but the next time you're out riding, pay close attention to the amount of handlebar movement required to initiate a 90 degree right turn. You'll find that it's surprisingly little, and it's safe to say that you won't want to move the handlebars that far when trying to go in a straight line.

One other thing which was entirely predictable is that when pulling the handlebars hard from one side to the other, it's very easy to unintentionally push harder against the pedals than necessary, resulting in big power spikes. Fortunately the hill was more than half a mile long, so I had plenty of time to adjust my pedal strokes to smooth out the power delivery. At a modest pace with a power output of 200 watts, pedaling at a slow cadence uphill produced the desired result: I got the handlebars movements perfectly synchronized with the pedal strokes, just as demonstrated in Jim's video. The result? Nothing. No change at all in power output. Did that prove the technique doesn't work? Not necessarily. One could always claim (albeit without an ounce of supporting evidence) that the technique was working but that I was unaware of it. Perhaps my arm movements really were relieving my legs of some of the workload, and it was just pure coincidence that I was producing the same power pedaling with and without waggling the handlebars. Or one could claim that at such a low power output, wagging the handlebars doesn't contribute enough to the power stroke to be noticeable. Jim however claims a whopping 30% power increase in his tests, even at fairly modest power outputs, so my results certainly casts doubt on that claim. These kinds of objections are also a double edge sword, because I could argue that the people claiming to see an increase in power output when wagging the handlebars are only fooling themselves into seeing what they expect/want to see. The paucity of corroborating data certainly suggests that this may just be a case of belief masquerading as reality. But as I've said many times before, no amount of counter-evidence can defeat the objection that, "You just weren't doing it right." The fact that unfalsifiable claims like that cannot be disproved will always make them a safe refuge for lazy thinkers. They won't be able to hide there for long however, because the burden of proof rests with those making the claim, not those doubting it.

 

[trplay]

I’ve spent 7 hours riding on the zig-zag contraption trying to master the beast and have had some success. I also significantly warped a rear wheel wheel in the process. It went like this. I simply rode around the Zwift Innsbruck route at a cruising pace. If I wanted to chase someone I did, but mostly I simply cruised at an 80-120 watt level getting use to the bike. So here’s some more voodoo meaningless data.

In a nut shell these were my readings. When I went from a leg only pedaling stroke to a push pull I saw an increase of cadence of around 10 rpm while the wattage will jump up to around 25-30 watts. If one uses the leg only method and increases the rpm to this same RPM the increase is only 10-15 watt increase. These numbers are consistent within the 50 -80 rpm pedal stroke range. There appears to be a 10-20 watt increase using the upper body. It is not free energy as the heart rate also increases. My mastery of the bike has not evolved so that I can pedal faster than 80/85 rpm without resulting in an inconsistent cadence. I have tried to push pull without increasing the cadence while keeping the same leg stroke but to date have been unsuccessful.

I would be interested in seeing others do this same goat rope to see if their numbers would come out remotely the same.

 

[LMT]

I would guess if he needed the trail vacated because of his excessive wobble he didn't use the correct technique. It would be better if he found someone who does understand the technique that could demonstrate this to him before he tries any more experimentation. Sounds like Osiris took a wrong turn to the Ball Room dancing class and ended up at a mud wrestling event.

+1

For me the whole upper body thing is not about moving the bottom bracket towards your foot you're about to drive with, it's about using the upper body as leverage which allows you to kick harder - the only wobble (which should be very little) should be the correction when going through the power phase when the BB moves away in the opposite direction to your driving foot which you then correct with your upper body. Using the upper body this way allows you to spread the load, great for sprinting or that extra oomph when going up short rollers. But for a long climb, the usual applies, good gearing, high cadence and no extra weight.

 

[RojoRacing]

Before reading this understand I’m not satisfied with the use of the words proactive and reactive so if when reading this you know of words better suited to this use I’m open to suggestions.

On a DF bike when standing we’re not pulling on the bars unless it’s an all out finish line sprint(more on this later) we are instead just rest our hands as normal. Standing is more a position change IE hip angle then it is anything else, we do it to use different leg muscles. On a cruzbike rocking the bars does nothing to change your body position or use different leg muscles.

So on a df road bike you don’t pull on the bars unless you’re putting out so much power you need a new anchor point to stabilize yourself. If you try to stand and put out 1000 watts of power only resting your hands on the hoods you’ll be all over the road and quickly in a ditch. So we have proactive actions and reactive actions going on here. On a DF bike(sub 500 watts) standing is the proactive function and the rocking action is a consequence or side effect. Now push you power north of 500 watts and the rocking is still a consequence but now you’ve added gripping and pulling on the bars to the side of proactive functions.

On a cruzbike you’re told to grip the bars and rocking back and forth as a form proactive function but is it really proactive when on a DF bike it’s always reactivate aka consequence? If it is indeed a consequence then where is the proactive function to the equation? Now when north of 500 watts on a cruzbike the rocking is a consequence of the extra sprinting power and gripping the bars and adding counter torque to the pedals is a proactive function to control that power.

Bonus round/example
On a SS MTB when climbing hills, well more like 15-20% mountains you need to stand for a different reason and that reason is you don’t weigh enough to mechanically push the pedal down. I know you’re thinking what? and that’s understandable because it’s a thing only applicable to bicycles in this situation. So you know how some people question how much we pull up on the pedals when clipped in? Well on a SS MTB on something crazy steep think sub 2 min efforts you push and pull on the pedals and should one foot come unclipped you’ll quickly find the foot pushing on the down stroke is suddenly being lifted up and you along with it. The simple fact is your own body weight isn’t enough to push the pedal because a SS with taller gearing lacks the mechanical gear ratio. With all that said there something else to point out and that’s the function of pulling on the bars. Pulling on the bars helps subsidize your lack of leg pulling power and keeps you stabilized at the same time.

 

[Steve Short]

I wish you guys would reach a conclusion to this argument so I can determine if I should get a Vendetta or not. 20 pages and no firm conclusion. I am so confused.

 

[Don1]

yes steve buy a v20 and be happy, live long, ride far. road bikes hurt

 

[RojoRacing]

I wish you guys would reach a conclusion to this argument so I can determine if I should get a Vendetta or not. 20 pages and no firm conclusion. I am so confused.

oh well the answer to your question is easy, YES. I mean who doesn't want to go farther, faster and in more comfort?

As for reaching an agreement on how much rocking the boom on a cruzbike helps or doesn't help is a mute point when the end results speak for themselves.