Climbing and Sprinting technical talk

[murmur]

Here's a variation on the wording of the thought-experiment from my first post in this thread: You can calculate the energy going into the drivetrain by looking at energy per rev going into the crank. Force times Distance (it's actually the component of Force in the direction of movement at every instant, times distance, but "Force times Distance" doesn't oversimplify.) gives you that energy. And at first, we assume the Force* as the pedal goes around the crank circle is the same for the MBB case as for the fixed BB case. So the same energy enters the drivetrain here. But the foot on the pedal doesn't move as far to do a rev, relative to the hip joint, in the MBB case. It only moves 93.5% of the fixed-BB distance. So less energy comes from the leg: 93.5% of the fixed-BB energy. Where's the remaining 6.5% (of the energy we know went into the drivetrain) come from? It comes from the force on the bars as they move, which is of course produced by the upper body.

Dave

*Unrelated to any metaphysics from the Star Wars universe.

 

[LarryOz]

Testing for these numbers in real life is going to take a serious data-gathering setup.

Why not use a pedal or crank based power system and a hub based system concurrently. Will need 2 head units to collect the 2 sets of data.
After you calibrate every and make sure they match perfectly, then it would seem that when riding on the road, the pedal/crank sytstem will only detect power at the crank, whereas the hub power system should detect the total.
One should be able to test this but making 2 run on a grade:
#1 - make the ride making sure you do not use any upper body
#2 - make the ride useing upper body input.

Compare all the power readings from both power setups. That should help prove how much upper body helps.

 

[Jim Parker]

Why not use a pedal or crank based power system and a hub based system concurrently. Will need 2 head units to collect the 2 sets of data.
After you calibrate every and make sure they match perfectly, then it would seem that when riding on the road, the pedal/crank sytstem will only detect power at the crank, whereas the hub power system should detect the total.
One should be able to test this but making 2 run on a grade:
#1 - make the ride making sure you do not use any upper body
#2 - make the ride useing upper body input.

Compare all the power readings from both power setups. That should help prove how much upper body helps.

Hi Larry,
According to the hypothesis I subscribe to, the power from the upper body is still going through the pedals/cranks. The force vectors from the upper body are summed with the force vectors from the legs, but those forces all converge at the pedal/crank.
Therefore, measuring power at the pedal or crank will include power from the upper body.
The set-up you describe would be useful for detecting inefficiencies in the drivetrain; i.e. power lost due to frame-flex, chain stretch, etc.

Jim

 

[LarryOz]

According to the hypothesis I subscribe to, the power from the upper body is still going through the pedals/cranks. The force vectors from the upper body are summed with the force vectors from the legs, but those forces all converge at the pedal/crank.
Therefore, measuring power at the pedal or crank will include power from the upper body.
The set-up you describe would be useful for detecting inefficiencies in the drivetrain; i.e. power lost due to frame-flex, chain stretch, etc.

Thanks Jim - I can see it all clearly now - and I thought I was on go something there.

 

[Balor]

By the way.

There are two pedalling styles available for recumbents - pushing with your quads like you do on DF...
And pulling the pedals down by flexing the knees at 'dead spots' that are not really 'dead' after all. On DF it is called 'scraping'.

"Scraping" the pedals comes with two advantages, due to downward (on a recumbent) force vector:

a. It uses conservative gravity as reaction force again.
b. Due to it being nearly parallel to steering axis, it provides no pedal feedback.

Unfortunately, this style of pedalling is very counterintuitive for DF riders, it uses muscles in an entirely different way and I'm not sure that you can train your calves and inner thighs to the point you can train your quads.
But as it is evidenced by Railgun seat (and it's 'howto' description), same applies to RWD bents too.

Note how the description dances around the 'tissues hysteresis loss factor' without actually mentioning it .
Work one leg against the other (one pulling while the other is pushing) to route as much power straight through the crankset instead of wasting it by using fewer available muscle groups and rerouting it through the seat back.

Cannot work this way, our 'pulling' muscles are too puny and weak genetically. But THIS actually works:

We find it is better to have a delayed power stroke, somewhat similar to what is taught for time trial bikes. Imagine you are looking at your crankset as a clock from the drive side of the bike. Divide the clock into (at least) four segments. Point your toes slightly forward (you may need to move your cleats rearward) and from :

• 10:00 to 1:00 - lift and press forward on the pedal. You should feel the top of your shoe pressing on the top of your foot.
• 1:00 to 4:00 - place the full weight of your leg on top of the pedal and press forward and down. The (rear) top of your pelvis, shoes and shoulders should be the primary points of contact.
• 4:00 to 7:00 - keep the weight of your leg on the pedal to push down and pull backwards.
• 7:00 to 10:00 - lift up on the pedal and and pull backwards.

But if you provide reaction force by pulling the bars, you end up with much fewer inefficiency than compressing your tissues with 20% loss factor, that your central governor likely notices and 'pulls the brake' pretty hard, at least this is the case in some, and I'm quite sure - most people who are not extremely well-trained athletes.
This is pretty much like the case of riding against the headwind - it is really hard to maintain same POWER against the headwind, as compared to riding inclines (where it is, in fact, easier - mentally, of course).
I can bet anything that this is due to central governor doing rough calculations on 'watts per mph', noticing a sharp spike and screaming - 'Stop wasting precious glucose, goddamnit!'.

 

[Balor]

By the way. I've been told that hysteresis of isolated piece of pig fat (that was evaluated in tests and resulted in about 20% of power dissipated), might differ drastically from hysteresis of living tissues.
And it is absolutely right!

Living tissue is full of blood and other bodily fluids (extracellular fluid) flowing throw tiny capillaries. When compressed and uncompressed, it would be forced though them back and forth, creating viscous friction. Does is sound familliar? That is exactly how oil dampers work.

Anyway, I've dug up this articles, but cannot make make sense of them:

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=imsediss
http://web.mst.edu/~stutts/SupplementalNotes/EqivalentViscousDamping.pdf

Anyone can comment?

 

[Balor]

http://www.ati-ia.com/es-MX/Library...nt and modeling of biomechanical response.pdf

Yet an other PDF with stuff that is way over my head to fully comprehend, except:

a. "biological soft tissues exhibit complex mechanical behavior including nonlinear, inhomogeneous, anisotropic, and rate-dependent response". Basically, the harder you push, the more they resist - and damp.
b. "When the response force is plotted as a function of displacement, pronounced hysteresis is observed [9] (Fig. 5B). This hysteresis is a consequence of the viscoelastic nature of the material, and the nonzero area enclosed by the curve represents loss of energy due to viscous damping."
b. Next, they feature stress relaxation, as in the longer you push, the less they push back on uncompression, hence low cadence would result in even more losses.

So, it neatly explains why trying to climb hill as one would do on an upright on non-MBB bike would result in losses in your own tissues due to viscous friction. How much - no idea, but likely pretty damn huge, if my own results are true. But again, I'm relatively fat, so I have more 'damping material', despite being relatively powerful (so, my climbing speed pretty much halved on a recumbent).
And it explains why pulling on bars to replace compression with tension as counterforce made me climb nearly as fast again - but my arms are not yet up to the task.

THIS is source of speed of FWD MBB recumbents and why they are so close to DF bicycles, for sure.

 

[jond]

According to the hypothesis I subscribe to,

hi jim

do you think the width of the bar and height of the bar have optimal settings for the production of upper body power.

i realise this would be handy for climbing and acceleration whilst impeding aero qualities.

i found it easier to produce wattage with the original cruzbike bars than a set of salsa cowbells which are narrower? early days and the power is coming back but i cant but help feel the split between legs and upper body has become more of a focus on the legs only. and it is harder to swing that boom now.

i.e greater leverage ability on wider bars and higher set bars.

do you agree?

i note however that despite the easier generation of power and the added positions the total output of power for me does not change substantially.

my best is around for 100klm tt 285 watts/80kg body and i am unable to better no matter the platform DF trike or cruzbike. it takes about 2 weeks riding to switch over the body to a different platform.

what i note is the ability of the cruzbike to facilitate varied body positions to enable slightly different muscle groups to operate and therefore i can recuperate better. i shift forward i shift back and then i swing the boom. and i am of course super comfy on the bike of choice the vendetta.

in summary i find it easier to make sustained power on the cruzbike and it may be 15 watts or so higher than trike or DF. and that wider bars help that power generation in all positions.

 

[LarryOz]

do you think the width of the bar and height of the bar have optimal settings for the production of upper body power.

My 2 cents:
Many people thought I gave up the ability to "make" power with my upper body when I went to the little 12" wide stubby handlebars to take advantage of the aero effect.
Per my testing those little stubby bars gained me about 1 kph.
I personally feel like when you are truly relaxed and riding normally on a Vendetta you are not using your upper body very much at all
Only when you what "more" power for a sprint or to get over a hill do you sit up a little and use your upper body.
Then and only then are you getting some added power, but it is of course at the expense of aero - which of course doesn't matter as much when you are going uphill at probably a slower rate.

Even so, I have come to believe that with those short stubby bars I was possibliy unable to keep the front part of the bike from gently occilating back and forth while riding, especially under strong wattage.
This I believe may have the affect of "stealing" power that was meant for the hub and wheel.
This would explain why my power output appeared to drop after I switched to my stubby bars. My speed did not though because of the aero advantage of the bars and my hands.
For me - I never count on being able produce any "upper body" power. My arms (even though massively huge for my size - haha - no I'm no Popeye) just can't compete with my legs! And my legs can't compete with Ratz's!

In the end everything is a trade-off. It takes many hours of experimentation to figure out what works best for you, and then with adaptation from one style to another, you might never know what is the most optimal.
Best to just have fun riding like the wind and passing all those "old fashioned bikes" - going up-hill preferably! <- This is what the DF guy looks like if you could see him as you pass

 

[jond]

passing all those "old fashioned bikes" - going up-hill preferably! <- This is what the DF guy looks like if you could see him as you pass

definitely blue blue in the face larry and green with speed envy

i should clarify and add the cruzbike bar is of course angled on the drops which allows greater and importantly much better control of the front end and thus moving the boom dynamically. in deed it becomes natural versus the bullhorns and salsa bars i have tried which are better aero but harder to control and involve.

5-6% extra power........... maybe.

advantage cruzbike.

 

[Balor]

Yet an other tidbit of data I've dug up:

Mechanics of Biological Systems and Materials, Volume 7 (google books), page one:

In this work, we measured the complex shear modulus of bovine muscle tissue, submerged in saline at bovine body temperature. (38 C)

The loss factor was highly consistent: 0.34 +- 0.035

Basically, 1/3 of power that would be spent compressing your not tensed muscle tissues (I doubt our muscle is drastically different from bovine) would be lost as heat.
I can bet fatty tissues are much worse than that.

 

[LarryOz]

submerged in saline at bovine body temperature.

I'm a little (ok - very) slow here, but are you saying... that if you ride your recumbent underwater at cow (bovine) body temperature that you will cause the water to heat up with 33% of your unused muscle power... or ...
that you muscle will turn into cow muscle when submerged at cow (bovine) body temperature whist riding??? It's all Greek (I mean cow.. I mean bovine) to me.

 

[JOSEPHWEISSERT]

Larry, Larry, Larry.

 

[Balor]

Yea, funny. Of course, testing human tissues in vivo would be preferable, but I bet they run into drastic shortage of volunteers .
Anyway, it means that whatever portion of energy you spend compressing your muscle tissues, would be returned only with 34% penalty.
Porcine fatty tissue, unheated and not in saline solution (hence, likely showing rather different mechanical properties) still shows loss factor of 22%.

 

[bladderhead]

If there was a race in saline at 38 C Larry would win

 

[Will Parker]

Sorry for the long post. I spent a long time with my dad this morning talking over the question of whether moving-bottom bracket cyclists really can add power with their upper bodies. Short answer: yes. Here are my thoughts.


In a moving-bottom bracket (MBB) bicycle such as standard road bikes and the Cruzbike, movement of the bottom bracket (BB) by the upper body--given certain conditions-- can add torque useful for propelling the bike.


This seemed illogical at first glance. “Power is generated on a bike,” I thought, “by the rotation of the pedals around the BB."


My first thought was right. Mostly. A bike is moved forward by rotating the BB axle, which is connected to a chain, which connects to the axle of the drive wheel. The BB axle is rotated by generating torque using the crank (lever) arm. The pedal is placed at the farthest point along this lever arm, in order to generate the maximum torque (a measure of “turning force” according to Wikipedia). This rotational force is equal to the force applied on the lever arm multiplied by the distance between the point where the force is applied and the point of rotation. For example, if I applied 10 pounds of force on the end of a 1 foot wrench, I would be generating 10 ft/lbs of torque around the nut I wanted to unscrew.


Given these basic facts, it seems impossible to add power to a bicycle by moving the BB. One would be applying a force at the point of rotation. Given that the distance between the point where the force is applied and the point of rotation is zero, and that zero multiplied by any force is zero, we find that torque would always be zero around the BB if one moved only the BB.


Thus, as a way of adding power to the forward motion of a bike in the traditional way of increasing the torque around the BB, moving the BB is useless. However, that does not mean it is useless as a way to add torque, and thus power, to move the the bike forward.


One must simply look at a different point of rotation: the pedal. Assuming our legs during certain phases of the pedaling cycle have momentary stiffness and are attached to the pedal (the conditions I alluded to above), the pedal can be seen (momentarily) as a fixed point about which to rotate the BB.


Imagine a bike floating in mid-air. Now, freeze a pedal in its current position in space. Now, rotate the bike (and thus the BB) around that pedal. What I hope you will see--besides a churning vortex of human-powered transportation technology-- is the BB axle rotating around a lever arm (the crank) around the frozen pedal. What I also hope you will see, is that the drive wheel of the bike will spin; the rotation of the BB around the pedal has generated torque which can drive the bike chain and thus the drive wheel.


The difference from the traditional source of power on a bike, is that the point of rotation is the pedal, not the BB. Two different points of rotation, two different ways of generating useful power for the drive wheel.


This means that in an MBB bike, whether an upright or a Cruzbike, power can be generated using the upper body, but only if the legs hold some rigidity, allowing the BB to move relative to the the pedal and generate torque. Theoretically, someone with two peg legs could generate power on an MBB bike with only his upper body, as long as the pegs held the pedals in place relative to the BB.


Working through these thought-experiments has convinced me that, indeed, useful power can be added to MBB bicycles by using the upper body to rotate the BB relative to the pedals.

 

[Robert Holler]

This is all fine and good on paper but from experience the real key here is getting your upper AND lower body into the right power position, and the terrain is critical to how the setup will impact performance. This is as important for your pedal to seat distance and it's even more critical for the arm position on a Cruzbike (if you are actually going for "max" performance) to be correct.

I see a lot of setups that put the upper body way out of position to actually generate power, but if the course is all flat and the goal is 100% aero - by all means that is a worthwhile trade off.

 

[murmur]

Robert, that raises the question of whether we need adjustable (as in on-the-fly adjustable) seat positioning like some mountain bikes have, to optimize the bike as terrain changes during a ride. And do we need an adjustable seat angle too, or is fore-aft position going to do it?

 

[ratz]

This is all fine and good on paper but from experience the real key here is getting your upper AND lower body into the right power position, and the terrain is critical to how the setup will impact performance. This is as important for your pedal to seat distance and it's even more critical for the arm position on a Cruzbike (if you are actually going for "max" performance) to be correct.

I see a lot of setups that put the upper body way out of position to actually generate power, but if the course is all flat and the goal is 100% aero - by all means that is a worthwhile trade off.

Yeah I've been following Jim's lead with the V20's; drops for power and hoods for aero; works well on the V chassis; with the curved boom we actually got pluckyblond dialed in too. last year we could only get 1 or the other on her Silvio. Perhaps some illustrated Robert on the bike photos would help to document that. Never could get both at the same time on the Yellow vendetta; the boom mount was a limiter.

 

[LarryOz]

Robert, that raises the question of whether we need adjustable (as in on-the-fly adjustable) seat positioning like some mountain bikes have, to optimize the bike as terrain changes during a ride. And do we need an adjustable seat angle too, or is fore-aft position going to do it?

I always thought that that would be a good idea.
I ride with a little 12" stubby (suicide bar - some call it), for aero of course - which I am pretty sure puts most of my upper body out of the power equation, but I can still go more down the road at an OK speed.
I thought that if you were going to be climbing quite a bit of steep hills, you would want to flair out the handlebars (auto-magically of course) and raise your seat to about 30 degrees.
I know I can make about 20% more power sitting up and that angle as apposed to laying back at 18 degrees.