Erg wattage vs Cycling wattage

[Nomath]

...
Its really not hard to see why there is a big power difference.

1. Your moving your entire bodyweight almost continuously on the rower. This is 100% power loss.
..

You may be right for the recovery phase, but not for the drive phase.
If the energy of moving your body in the drive would be lost, you would notice a very hard pull on the foot straps at the end of the drive. This is evidently not happening. With a bit of training you can row strapless. The energy for launching the body at the catch is used in the second part of the drive to pull the handle and bring your body to a standstill even before the final pull with the arms. With proper rowing technique there is zero loss in moving the body in the drive.

[MartinSH4321]

I agree that there seems to be a discrepancy with those times. My gut reaction is that it's a sample-size issue.

My own N1 sample is that the 2k/4k is my crossover point. Shorter than that is faster on the rower (the shorter the distance the more pronounced the difference). Longer is faster on the bike (predictably, the longer the duration the more pronounced the difference).

Have you ever tested 200m and max watts on the bike erg? If I remember right the WR for max watts on the bike is almost 2400W on a bike (Manfred Nürscheler) and on the static rower 0:59 pace or around 1700W, so almost 50% more on the bike but only for a few seconds.
This sounds right for me as the bike movement is more efficient and legs can produce a lot of force when anaerobic alactic, but lactic acid soon slows you down while on the rower you also have back and arm muscles to work with, so faster rows for 1'-4'.

Hahaha. Yes, and my max wattage is about 15% higher on the rower than the bike erg.

But, again, I think this is a "bike erg" specific issue. Though I have no personal experience, from speaking to others my max wattage would be much high (25ish%, maybe) on a Watt bike or other (presumably) a real bicycle.

***This discrepancy between the erg and other bike trainers seems to disappear for efforts longer than about 1 minute***

Yeah, this really looks like a bike erg issue!

And big congrats for your recent 1k PB, only about 1'' behind WR, absolutely amazing!!

[Nomath]

I only measure power from the bike erg. And actually, you raise an important point: I have been told by several persons that the bike erg under-reports power at high wattages. I have no explanation for that though.

Having delved in the physics and made own measurements of the flywheel speed, I see no way for this conjecture to stand. The physics of a rotating air fan is fairly basic. The power dissipation is determined from the drop in the flywheel speed and the moment of inertia of the flywheel and the air drag coefficient as parameters. Only if the air drag coefficient would change with the rotation speed, could there be a power calibration issue. I am possibly the only one outside the C2 engineers who has monitored the flywheel speed during the recovery phase of high power rowing strokes (800W average ; 2000W peak), but I didn't observe a change in drag coefficient with speed. See viewtopic.php?f=7&t=203038&start=15#p544053

Calibrating cycling power meters is not easy. It requires a comparison on a device where you can determine power from basic principles. Such a device is a treadmill set under an exactly measured gradient.
According to this study, a power measurement in the pedals or in the cranks will be about 1.5% + 3W higher than a power measurement in the rear wheel. I guess the same drive-train losses apply to the BikeErg. This amounts to about 10 W drive-train losses at 500W input.

[Carl Watts]

...
Its really not hard to see why there is a big power difference.

1. Your moving your entire bodyweight almost continuously on the rower. This is 100% power loss.
..

You may be right for the recovery phase, but not for the drive phase.
If the energy of moving your body in the drive would be lost, you would notice a very hard pull on the foot straps at the end of the drive. This is evidently not happening. With a bit of training you can row strapless. The energy for launching the body at the catch is used in the second part of the drive to pull the handle and bring your body to a standstill even before the final pull with the arms. With proper rowing technique there is zero loss in moving the body in the drive.

Err so when you move your body up and down the slide with no load your using no energy ?

It takes energy to accelerate a mass and the higher the rating the higher the losses. That energy doesn't go into the flywheel its lost.

The losses are significant and would be the largest part of the difference between the rowing and cycling.

The only thing I left off the list was gears. Gears on the bike allow you to optimize the power band, there are no gears on the rower its like riding a fixed wheel bike which only works for very specific velodrome events but when's the last time you saw someone riding a bike with 1 gear in the tour de France ?

The rower has absolutely no advantages over the bike in producing raw power, the bike wins every time.

[Nomath]

Err so when you move your body up and down the slide with no load your using no energy ?

Try to move your body up the slide with no handle and without foot straps. You will be flying backwards when the seat touches the back stop.

[Carl Watts]

Err so when you move your body up and down the slide with no load your using no energy ?

Try to move your body up the slide with no handle and without foot straps. You will be flying backwards when the seat touches the back stop.

Other people have already done the math in other threads. Basically I'm 100Kg moving up the slide at 2m/sec according to ErgData. Its been to long since I did Physics but you would need to convert the Kinetic energy to Joules then Watts, something like that but the answer is not zero. Thats just the drive then you have the recovery and thats without the arms.

The reason your heartrate is higher on the Erg for the same power on the bike is that your having to compensate for the wasted energy moving up and down the slide as well as a less efficient motion for the body to complete to get the power to the flywheel,its that simple.

Try different ratings at the same pace. I do 2:04 pace at 17spm as its the most efficient and results in the lowest HR for me. If I rate up I waste more energy going up and down the slide and if I rate lower the body just hates the massive power increase due to the shorter duration you can make power for. Either way on the wrong side my HR increases.

[Tsnor]

I only measure power from the bike erg. And actually, you raise an important point: I have been told by several persons that the bike erg under-reports power at high wattages. I have no explanation for that though.

Having delved in the physics and made own measurements of the flywheel speed, I see no way for this conjecture to stand. The physics of a rotating air fan is fairly basic.

look at the power production side of the equation. Stationary bikes do not allow the critical angle change required by sprinters to get full body (not just legs) into a sprint. Comparisons of a sprinter on a road bike with power meter on the road vs. exactly the same bike with the exact same power meter mounted on a wheel based resistance trainer show measured 200+ watts difference for very high output short duration events. This comes from lower power production, not measurement error. If the reports were comparing a bikeErg with a power meter equipped road bike the there could easily be a 200+ watt "underreport", even if the bike erg fan based measurement system was flawless.

[jamesg]

The energy for launching the body at the catch is used in the second part of the drive to pull the handle and bring your body to a standstill even before the final pull with the arms.

"Used in the second part": only if we pull the handle, which is in itself work done. Kinetic energy can be recovered only by storing it as potential energy (height) or in something elastic. Examples are pendulums and rubber balls.

We are not like these. In their absence, to change the direction of motion is an acceleration, so requires work; the typical example is driving a car round a hairpin bend. If we don't open the gas, the car decelerates, i.e. does work and loses energy. Running in circles is much harder than going straight: speed may be constant, but not velocity, so it's continuous acceleration. Skipping woud be a cinch if we could stay rigid and bounce off the floor.

Another example is walking downhill. This can be very hard work, despite the help we get from gravity, because we have to stop ourselves; using muscle in eccentric.

There's no point in comparing bike and rowerg power: use of most muscle groups including small ones in sequence, transmission through arms back and shoulders, different training, need to accelerate body mass, long times when no energy is being delivered to the handle, limits to peak force, dodgy technique together ensure that rowing is not an efficient way of delivering power.

All we can do to improve efficiency on an erg is put it on slides and learn to row without spurious action, like any good crew.

So what, it gets us fit anyway, and maybe more so, thanks to the use of more muscle over a wider range of movement.

[JaapvanE]

I don't have the software to do this search, nor the ambition to do this tedious work. It's a huge task. I believe my comparison-of-medians approach provides a credible estimate of the power differences. It's far below the conjectured 30%.

The risk is that you compare two totally different groups of users. Where Concept2 dominates the competitive rowing field (and PR's might contain several Olympic and world champions), I don't have that impression for biking as Tracx and the like are more important players there. That would introduce a huge bias in your data.

[JaapvanE]

Having delved in the physics and made own measurements of the flywheel speed, I see no way for this conjecture to stand. The physics of a rotating air fan is fairly basic. The power dissipation is determined from the drop in the flywheel speed and the moment of inertia of the flywheel and the air drag coefficient as parameters.

Do bikes have a moment where they can measure this? A bike stroke is pretty much continous power, so measuring the coadt down of the flywheel can only be done after the training?

[Nomath]

Having delved in the physics and made own measurements of the flywheel speed, I see no way for this conjecture to stand. The physics of a rotating air fan is fairly basic. The power dissipation is determined from the drop in the flywheel speed and the moment of inertia of the flywheel and the air drag coefficient as parameters.

Do bikes have a moment where they can measure this? A bike stroke is pretty much continous power, so measuring the coadt down of the flywheel can only be done after the training?

My remark that the power dissipation is determined from the drop in flywheel speed and the moment of inertia of the flywheel and the air drag coefficients as parameters, is a bit sloppy.
I should have said : my measurements of the flywheel speed during the coast down (zero power input) show that the rotation time increases linearly with time. Therefore the drag coefficient does not change with speed. If there is continuous power input, as on a bike erg, and the flywheel speed is constant, the power dissipation is equal to product of the drag coefficient and the angular velocity of the flywheel to the power 3.

[Nomath]

"Used in the second part": only if we pull the handle, which is in itself work done. Kinetic energy can be recovered only by storing it as potential energy (height) or in something elastic. Examples are pendulums and rubber balls.

We are not like these. ...

Somewhere on the slide, say halfway, your body reaches a top speed, say 1.5 m/sec. Well before the end of the slide the speed of the body is zero. According to Newton's laws you need a force to decelerate a moving mass. Where does that force come from?

[Nomath]

The risk is that you compare two totally different groups of users. Where Concept2 dominates the competitive rowing field (and PR's might contain several Olympic and world champions), I don't have that impression for biking as Tracx and the like are more important players there. That would introduce a huge bias in your data.

I think that the elite bias has disappeared when you compare the medians.

[JaapvanE]

I think that the elite bias has disappeared when you compare the medians.

Depends on how consistent these athletes are. A key issue is that a lot of them probably are humped together as they strive for the same WR times and it becomes more and more difficult to squeeze out that last second to reach that world record. But given enough recreational rowers, that might balance out.

[JaapvanE]

my measurements of the flywheel speed during the coast down (zero power input) show that the rotation time increases linearly with time. Therefore the drag coefficient does not change with speed. If there is continuous power input, as on a bike erg, and the flywheel speed is constant, the power dissipation is equal to product of the drag coefficient and the angular velocity of the flywheel to the power 3.

True.