Efficiency thread

Triathlon Forum
1

The last “aero’wind tunnel et al” thread got me thinking about overall pedaling efficiency again.

The typical cyclist gets power to the wheel at about a 20% efficiency, with a range from about 16-23%. this is about half the overall efficiency of the contracting muscle in converting chemical energy into work. So, there is a lot of room for improvement.

I have thought that a lot of this inefficiency was lost in the pedaling motion, i.e., the energy required to make the legs go around and working against oneself on the upstroke. Another loss is friction losses in the bearings and chain, but these are generally acknowledged as small. Now, it seems, that there is another potential source, losses due to unsteady power production causing constant small acceleration/deceleration of the bicycle.

Clearly there is lots of potential for improvement if only the source of all of these losses could be identified and quantified, which would allow us to concentrate on where the biggest gains can be made. Has anyone ever looked at identifying and quantifying the source of these inefficiencies experiementally? Does anyone have any other ideas regarding other potential areas of loss? Does anyone have any sense of the various magnitude of the above identified sources of loss? I will put down my guestimates below assuming the total inefficiency is 50%:

  1. Working against oneself - 20%
  2. Pedaling motion inefficiency - 20%
  3. Drive train friction - 5%
  4. Unequal power application loss - 5%

Frank

2

not quite sure I understand ‘20% working against yourself’

I believe that John Cobb states that about 75% of a cyclists effort goes to overcoming wind resistance.

3

Gary writes: "not quite sure I understand '20% working against yourself … I believe that John Cobb states that about 75% of a cyclists effort goes to overcoming wind resistance. "

Working against yourself refers to the non-tangential application of pedal force around the pedaling circle and the pushing up of the recovery leg - the main inefficiency that PC’s address.

John Cobb is wrong unless by effort he means driving power delivered to the drive train. Then there are only three main losses. 1. drive train losses. 2. rolling and bearing resistance losses. and 3. wind resistance. The higher the speed the more wind resistance is prominent and 75% is a good number of the total of these three.

What I mean by effort is energy expended by the athlete trying to perform the athletic endeavor. All of the above losses are still present but I don’t count wind resistance or rolling resistance as an inefficiency as the question deals with inefficiencies involved in getting power to the wheel, not what happens after it is there.

Frank

4

Gary writes: "not quite sure I understand '20% working against yourself … I believe that John Cobb states that about 75% of a cyclists effort goes to overcoming wind resistance. "

Working against yourself refers to the non-tangential application of pedal force around the pedaling circle and the pushing up of the recovery leg - the main inefficiency that PC’s address.

John Cobb is wrong unless by effort he means driving power delivered to the drive train. Then there are only three main losses. 1. drive train losses. 2. rolling and bearing resistance losses. and 3. wind resistance. The higher the speed the more wind resistance is prominent and 75% is a good number of the total of these three.

What I mean by effort is energy expended by the athlete trying to perform the athletic endeavor. All of the above losses are still present but I don’t count wind resistance or rolling resistance as an inefficiency as the question deals with inefficiencies involved in getting power to the wheel, not what happens after it is there.

Frank

have you seen this?

http://bicyclesports.com/images/article/chart.gif

5

I have not seen that chart but it certainly raises some questions and has nothing to do with what my question was. This chart apparently deals with how the energy is distributed that is actually put into the drive train by the cyclist. My question is where does the energy go that is expended by the athlete but does not enter the drive train (or get to the wheel). At least this chart has a value for one of the components I talked about, drivetrain and bearing friction.

questions raised by the chart.

  1. What constitutes potential energy change? Makes no sense to me unless he is talking about climbing a mountain. Most courses start and stop at the same elevation so there should be no overall potential energy expenditure.

  2. What constitutes kinetic energy change? Does he mean energy required to accelerate the bike up to speed at the start and after braking and cornering?

6

There are inefficiencies in muscles due to friction in the muscle tissue itself and the surrounding sheath. I’m not sure if anything can be done about those, except maybe good hydration? I guess they could be called “physiological friction” or something like that.

There is also the friction in the joint (probably nearly zero!).

There can be significant “drag” or resistance from the opposing muscle group. How about biofeedback of opposing muscle groups…trying to completely relax the muscle group not actively involved in drivetrain-power-producing force at the various crank angles? I’m guessing that faster rpms (I’m referring to REALLY faster, such as 140 and above) may help to do this…you need to be able to relax in order to do this for very long. If you look at good running sprinters, they don’t look very tense…like a bodybuilder posing. Top sprinters leg muscles look alternatingly very taught and then relaxed on each stride. If this opposing relaxation is possible to train to some degree, it certainly could increase power delivered to the pedal by decreasing power wasted to move the limb in a given direction (something I think training on PCs do for me, i.e., increase power to the drivetrain by decreasing extensor power I previously used to raise the opposing leg).

7

With circular pedaling the power is applied from the
knee with direct downward pressure, using the lower
back for resistance ( the root cause of all lower back
pain) and as the back is moving some power is lost.
With Anquetil’s linear pedaling, leverage is used when applying the pedal power and all resistance comes from the hips which are firmly fixed on the
saddle, so there is no loss when applying the power.
Circular pedaling creates the dead spot area which
causes the interruption in power application while
linear pedaling has no dead spot area and gives
continuous smooth power application.

8

Gary - John Cobb’s graph is where the power that is supplied to the rear wheel goes. Frank is wondering how much energy is applied to the pedals verses how much energy actually gets to the rear wheel.

Frank - I wish I had time to really give you my true thoughts on all of this. But it would be quitely lengthy. First off - Look back at the graphs in the famous Coyle study. You will see the two graphs of the forces being applied to the pedals. One graph is of the horizontal force and the other is of the vertical force. If you look at the vertical force graph (group 1’s average) you will quickly notice the large amount of force being applied during 150 - 190 degrees. This force application is basically wasted, because at this angle less than 50% of the force to the pedals actually goes to turn the pedals. If that weren’t bad enough, look at the horizontal graph. The peak force is applied at 90 degrees. Quite simply none of this force goes to turn the pedals.

So yes there is extensive wasted forces being applied to the pedals.

Please before some of you disagree, I suggest that you run the formula for determining the torque generated by the force applied. The formula for the the torque generated by the vertical force is Torque = force x crank arm length x cosine of the crank angle. At 90 degrees the value for cosine is zero. So none of this force gets turned into torque. Oh yea, for vertical force its Torque = force x crank arm length x sine of the crank angle. At 150 degrees it is 0.50 and drops to 0 at 180 degrees. therefore any force being applied through this portion of the crank angle is basically wasted as well.

9

I agree those are also inefficiencies but I think they are generally small, except for the relaxation of the opposing muscle you mention which can be trained. The best example of training to relaxation is the heart. Improved relaxation is the reason the heart rate goes down with training. Imporved relaxation allows for improved filling, larger stroke volumes, and, lower heart rates. Interestingly, it takes energy for a muscle to relax, albeit, less than what it takes to contract, so it it is more efficient overall.

One of the things a baby is doing when learning to walk and run is training what is called reciprocaal inhibition. The more we do an activity the better trained we become at this “relaxation” part of the coordinated effort. I agree that PC’s work on this aspect of the coordination. Perhaps that is where some of the early PC running improvement peple see is coming from?

Clearly, there are some inefficiencies that cannot be completely overcome, such as internal friction in muscle and joints. But, these are small (less than 1%, at high power, on my scale, I think) and the same for everyone.

Thanks for the input

10

I just wish I knew what you mean by linear pedaling or circular pedaling. When you say linear pedaling I think you mean what I call circular pedaling, but I have no clue.

I will say this, pushing down requires the contraction of the gluts, which insert on the pelvis. The hip joint cannot offer any resistance. The back is used to stabilize the pelvis, even using your technique. I don’t see how the saddle stabilizes the pelvis when one is pushing down on the pedal which is the same as pushing the butt up off of the saddle. Your description of what is going on in your (or Anquetil’s) technique is indecipherable to a medical person.

11

By circular pedaling I mean the normal recommended round style, pressing down, scraping
the shoe at the bottom of the pedal stroke etc.,
mentally you are using a circle.
Linear pedaling mentally uses two lines in V shape.
Direct downward pedal pressure is never used so
there is no rising off the saddle, no matter how hard
you are applying the power to the pedals. One other
terrific advantage with linear pedaling is that if
extra power is needed, maximum use can be made
of arm resistance when seated in the saddle and
travelling at speed. The fact that power is applied to
the pedals by leverage instead of downward pressure
from the knee greatly reduces the workload on the
knees and the risk of injury.

12

I think you will find that normal pedaling hardly ever involves direct downward pressure on the pedals. It sounds like your linear pedaling technique is simply what most people refer to as circular pedaling, that is, trying to follow the direction of the pedal with your applied forces. You may be thinking about it differently but you are trying to achieve the same thing.

13

I am completely perplexed by this whole “torque” thing as described here. It’s been a few years since I took Statics/Dynamics but as I recall: Torque = Rvector “cross” Force-vector. Thus Torque is a vector with a direction perpendicular to both the Rvector (the linear vector from the force application point to the torque generation point), and the Force-vector.

A magnitude of torque is attainable by multiplying the magnitudes of the Rvector (length of crank-arm) and the Force-vector and the “sine” of the angle between them.

On a bike, a person generates torque in the crank. If one is pedalling nice round circles, the force application is always perpendicular to the crank-arms. So the angle is always 90, and sine of 90 is 1 (max).

By contrast, if one is standing on a pedal at the bottom (not rotating), the force application direction is parallel to the line of the crank-arm, the angle is 0 (or 180), and sine of the angle is 0. That’s why standing on the pedal at the bottom does not generate rotation, even though the force is maximal.

The torque generated in the crank is not used in the crank, but is converted back into a linear force in the chain: the new Rvector is the line from the center of the crank to the top where the tangent chain contacts the chain-ring, and the new Force-vector is along the top of the chain. These are nearly perpendicular; designed that way for obvious reasons.

The force in the chain is converted back into a torque in the rear wheel, driving it. Again the R-F angle is nearly 90 for maximum transmission.

Going back to the point of initial power generation (the crank), the basic assumption made above for maximal generation was “pedalling round circles”. By contrast: If the only force generated were an up and down force (similar to what happens when pedalling out of the saddle, or pistoning), then the F-vector is only perpendicular to the cranks at 3-oclock and 9-oclock positions. At 12 and 6-oclock positions, the F-vector will be parallel to the R-vector producing Zero Torque.

But… Force application and conversion is only part of the story. Energy conversions and work need to be addressed in this equation as well. Unfortunately, we’re getting WAY off the subject of the original post and for that I apologise.

I did (somewhat) follow what you were driving at Frank. Unfortunately, my knowledge of biomechanics is minimal so I don’t feel qualified to properly address your points. I do have some thoughts, but no real answers for you. Personally, I’d combine 2 & 4: these would be conversions of energy in the muscle (heat) due to less than perfect (muscularly) pedalling. I think this is your primary area of concern. Number 3 seems somewhat irrelevant to your concerns (non-muscular). Your estimate for 1 seems right to me: energy lost due to the need to recover the leg to the top. Pulling up on the pedal (round pedalling) ensures continuous power transmission to the wheel, but a portion of that “pull-up” energy is used simply to raise the leg, foot, shoe, and pedal. Some of that energy might be recovered on the downstroke, but there would be losses. Good luck, and I look forward to hearing about any conclusions you reach.

Adam

14

Pulling up on the pedal (round pedalling) ensures continuous power transmission to the wheel, but a portion of that “pull-up” energy is used simply to raise the leg, foot, shoe, and pedal.
Don’t forget the energy needed to raise the cranks! Believe me, after 3 hours on the PC’s on Saturday, I was cursing the fact that the damn things probably weigh more than my frame :slight_smile:

15

I agree that the energy used to lift the leg/cranks is huge. Perhaps this is why Franks recommends a slightly lower RPM pedalling, since it means lifting your legs less times per minute.

I got my PC’s a short while ago (2 months). 6 Weeks ago I started riding outside and have built up to 4 rides in excess of 150 K (three 180K rides). What I found is that when I went for a hilly ride, I could last for ~5.5 hours without blowing up, largely due to the lower cadence and rests on downhills. This past weekend, I did a totally flat 180K ride with the boys and totally blew apart at 120K (after 4 hours) as I tried to maintain a cadence of ~100 RPM. I could barely move the pedals around for the final 60K. Luckily the “peloton” had mercy and towed me home. I can’t believe how much energy you use getting your legs over the top. You really need PC’s to appreciate this. Either way I am unsure what the efficiency equation is overall. All I know is that there is a lot of energy spent just moving your body parts around with not much going to moving the bike forward. If you don’t believe it, stand in front of your computer and turn one leg around in circles as if riding a bike and see how long you last :slight_smile:

16

That lifting the leg really isn’t an energy loss though as it is simply increasing the potential energy of that leg/crank combination, which one gets back entirely on the down stroke. All the PC’s force you to do is use new muscles to put that energy into the system - no cheating using the other leg to do it.

Another source of loss though, that someone reminded me in a private message, is frame flex. probably small, again, in most bikes, but present none-the-less.

17

The frame flex thing has always interested me. Back in the dark ages, I had one of the (then) new Cannondale big tubed aluminum bikes. It was rigid. I planned to use it in Criteriums and mountain climbs because of the rigidity and assumed increased efficiency over my SLX steel frame. I could feel the flex in the SLX frame very easily, and could, without shifting, alternately rub both sides of a properly adjusted front derailler when I put the hammer down…I mean, this frame was a noodle compared to the Cannondale.

I always sprinted better on the Cannondale, but darned if I didn’t ALWAYS climb better on the SLX noodle. I was obviously bending the SLX frame, but it felt springy to the point that I felt I got some of that energy back when climbing. If this was true, I imagine one could have detected some of the flex as heat, and therefore lost power, in the frame tubing. But, maybe I was recapturing some of this flex in my pedal stroke. I never really knew why I climbed better on the noodle except for this possibility. BTW, the SLX frame was heavier, too.

All that being said, Ves Mandaric says that he thinks the Carbo Mariola (with a carbon seat stay system) may be more efficient than the regular Mariola because of the Carbo’s increased rear triangle stiffness. This makes sense to me, but I don’t have both bikes to be able to compare them to see if there is a difference, or if it is measureable in my riding style. Otherwise the Carbo is somewhat flexible in a very comfortable way (it reminds me of the comfort of my old SLX frame, but without the wimpiness), and I’m faster climbing on the Carbo than on a full carbon (stiffer) Kestrel Talon. But, the Carbo is a lighter, which could be part of the difference between these two bikes.

In both cases though, I am faster on a hillclimb on the more flexible of the bikes which were tested head to head…go figure! This efficiency thing may be more difficult to decipher than current math formulae can provide…after all, there is a human component; with all of the variables that brings to the table.

18

yaqui writes: "This efficiency thing may be more difficult to decipher than current math formulae can provide…after all, there is a human component; with all of the variables that brings to the table. "

Agreed. All I know is there are lots of inefficiencies abut if we don’t know about them we can’t improve them, if it is possible to improve them.

A springy bike could be an advantage. I would have imagined such flexing would absorbe energy rather than give it back on most frames, but maybe not all, or, maybe, even, most.

19

I think you will find that normal pedaling hardly ever involves direct downward pressure on the pedals. It sounds like your linear pedaling technique is simply what most people refer to as circular pedaling, that is, trying to follow the direction of the pedal with your applied forces. You may be thinking about it differently but you are trying to achieve the same thing.

There has always been three unsolved problems
in cycling, Anquetil’s mysterious extra pedal power in
time trials, the dead spot area and persistant serious
on the bike lower back pain. By solving the first one,
you automatically solve all three.
Anquetil pedaled with his toes pointed down and many riders tried to copy this toes down style but
not one rider could come anywhere near his power.
This was because his toes down style was the result
of the completely different way that he used his leg
and arm muscles when generating and applying the
power to the pedals. If believing as you do that you
have to use round pedaling, this toes down style
will probably result in less power and calf strain.
His power came from being able to start his
main power stroke at 11 o’clock instead of 1 o’clock
and from the ability to combine and synchronize arm
resistance and leg muscle power.
The elimination of all back pain comes from the fact
that his power generating technique has the same
effect on the back as lifting a weight in the safe
recommended way, while normal round pedaling
has the same effect as using the dangerous method
of lifting.
You should have a look at that video and see the
man himself in action.
You will not get a more efficient pedaling style and
his time trial victories by big margins are proof of
that.

20

Get a life Noel.