Concept2 Forum

Hiya,
I'm going to probably figure this out for myself in the next while when I start measuring my performance on the erg in watts/time rather than the distance/time metric I've been using. Thought it would be an interesting question to ask though.

For those of you who also train on a bike, or 'smart-trainer' how does your watts performance on the bike compare to that on the erg? For example, if someone has a 250 ftp (an estimate indicating a person 'should' be able to sustain 250 watts for an hour) does this equate to something similar on the erg/rower? If not, is there a general ratio some of you have stumbled upon?

I have a new smart trainer for my bike and am loving that thing -- like a video game attached to my bike that makes me sweat buckets!

Well if you want to enter a Concept 2 Challenge on your ErgBike they halve the meters which should tell you something.

Essentially its alot easier to make power on a bike, the legs assist one another and the power output is more constant from your body. The Erg is just plain nasty with you only putting in power to the flywheel half the time and at lower ratings its even worse and it can be 1/3 of the time heading for 1/4 of the time and your also shifting your bodyweight up and down the slide.

Really hope that 2020 is the year that Zwift get a decent Erg power conversion to actual road speed on a bike.

Carl Watts wrote: ↑

January 13th, 2020, 10:41 pm

Well if you want to enter a Concept 2 Challenge on your ErgBike they halve the meters which should tell you something.

Thanks -- that does tell me something ! I can enter a concept 2 challenge on an ergbike??? how weird, it never crossed my mind.

50% is a nasty cut in efficiency... I guess that's why we have bikes and not rowing machines on wheels


(add) did a quick google search, see that C2 makes a bike, so I guess I can't use 'erg mode' on one of the various apps available for my trainer. The Tacx program is pretty cool, they have videotaped rides with corresponding slopes etc. that take you through the countryside, or city, or wherever -- very cool. A bit tricky to stay settled in my zone though when some random from wherever zips past me... so you know, sometimes I don't. lol

left coaster wrote: ↑

January 14th, 2020, 12:56 am

50% is a nasty cut in efficiency... I guess that's why we have bikes and not rowing machines on wheels

Your next new toy: https://www.youtube.com/watch?v=pLXuZKpNw14

On an BikeErg you make 2x the meters compared to rower or skierg when doing the same watts. If you do 203W for 1h you have 15k on rower and skierg, but 30k on the BikeErg.
I estimate C2 cuts the BikeErg meters in half for the challenges to make the efforts more comparable. For challenges, if I do 203W for 1h I get 15k challenge-meters, no matter if I did it on BikeErg, rower or SkiErg.

Do you mean on a road bike outdoors or on a bike erg indoors?

On a road bike outdoors on a flat road, there are two resistance forces : air resistance and rolling resistance. On pavement above 20 km/h, the air resistance dominates. The power needed to deal with the air resistance, in the absence of wind or drafting, is proportional to speed to the power 3. The formula is P-air = ½ x rho x Cd x A x v³ , where rho = air density, A is frontal area, Cd is aerodynamic drag coefficient, v = speed. The value of the combined factor CdA depends on the size and position of the rider, but a reasonable approximation is CdA =0.40 m² for a rider on a road bike in touring position and CdA = 0.32 m² for a rider in tight clothing on a racing bike in crouched position (I took these numbers from D.G. Wilson, Bicycle Science, p. 188).
Together with rho = 1.225 kg/m³ at sea level, you arrive at P-air = 0.245 v³ (touring) or P-air = 0.196 v³ (racing), v in m/sec.
Compare this with the pace-to-power formula for the C2 rowing erg : P-row = 2.80 v³ , v in m/sec.

The most interesting point is that both sport tools have a similar power-to-speed response.
In terms of distance covered in a certain amount of time for the same power input, you get: D-row/D-bike = 0.44 (touring bike) or 0.41 (racing bike).

For a more accurate comparison, one should add the rolling resistance power for the outdoor bike and the power for moving the body back-and-forth on an indoor rower. The former is of the order of 35W at 36 km/h. The latter more like 20W.

I have no practical experience on the C2 bike-erg. The fact that it uses the same flywheel-turbine as the row-erg for creating resistance is no doubt a key selling point. It gives the indoor-cyclist the same power-to-speed feel as on an outdoor bike. Factors like body position and size are irrelevant indoors. If it is true that on the C2 bike-erg you make twice the meters of a row-erg for the same power, the assumed CdA value is more like 0.63, as in upright position on a commuting bike.

I was talking about the C2 BikeErg and how the meters are counted for challenges and normal season/lifetime meters, pace is calculated exactly like for the rower but doubled, and only depending on watts generated.

Thanks for the replies.

I just dropped some change on a Tacx Neo 2t smart trainer and have quickly come to love it. The interactive apps are entertaining and the road feel can be dialed in by including your weight and the projected rolling and wind resistance of the bike you normally ride, they have settings for triathlon, road and mountain bikes.

On my second of 2 recovery days, back at it tomorrow. The C2 bike is specifically callibrated to allow comparison with the erg, I don't think the watts output on my trainer will ever be useful, it's also easy to cheat -- just go into the settings and drop your weight by 50lbs and suddenly you're flying past folks.

I think there are some interactive apps for the erg as well, I just haven't got there quite yet. Riding is something I actually do in the warmer months but in spite of the interest I've never made it into a boat even though I've had the erg for a few years now.

I should add....

My initial question was about ability to maintain watts on the a trainer/bike vs. erg.

I think the distance covered on the c2 bike was conflated with watts.

to put it another way: has anyone done a max low pull measured in watts and compared this to the max watts output they can generate on a bike?

Somehow I would think that it might be possible to get a higher watts max effort on the erg given how many more muscles are in use... will need to do the suffering to figure this out for myself.

C2 machines with air braked fans measure power by observing fan deceleration when not driven by the user. Other numbers (meters, pace etc) derive from power using a cube rule and an arbitrary constant: W = kV³, with V in m/s. It would seem that the constants used by C2 are k = 2.8 for rowers and 2.8/8 = 0.35 for bikes, because water offers more resistance than air; and to get a simple multiple (2) for the "meters".

You'll need to do some testing to see if you are better at producing power by oar or by bike. In general rowing has higher inertial losses and is more discontinuous, but personal charcteristics could well be enough to override these differences.

It's just possible that equivalent perfomance on the two could indicate perfect rowing technique, given the large effects of bad, so such testing could be very useful, however roundabout a method.

Here's a link regarding rowing efficiency (it's german, but the summary is also in english):
https://link.springer.com/chapter/10.10 ... 0301-0_127
The conclusion: biking has a much better efficiency factor than rowing, 0,23 vs. 0,19. Rowing at 190W has the same energy consuption as biking at 230W.

left coaster wrote: ↑

January 18th, 2020, 7:48 pm

I should add....

My initial question was about ability to maintain watts on the a trainer/bike vs. erg.

I think the distance covered on the c2 bike was conflated with watts.

to put it another way: has anyone done a max low pull measured in watts and compared this to the max watts output they can generate on a bike?

Somehow I would think that it might be possible to get a higher watts max effort on the erg given how many more muscles are in use... will need to do the suffering to figure this out for myself.

The best LP is around 1:00 pace, so about 1500W, the strongest biker can produce about 2300W. I estimate it's because you need about half the time for recovery at rowing.

left coaster wrote: ↑

January 18th, 2020, 7:48 pm

Somehow I would think that it might be possible to get a higher watts max effort on the erg given how many more muscles are in use... will need to do the suffering to figure this out for myself.

Already a long time ago, in 1988, a prominent scientist specialized in rowing performance, F.C. Hagerman, has found that your hypothesis is not confirmed. He found that the average maximal power for rowing is lower than the average maximal power for cycling, for all ages and for both men and women. The average difference, 207W (cycling) versus 195W (rowing), is not spectacular but significant. Unfortunately the full article is only accessible after paying a hefty fee, but the summary can be read free of charge : https://www.ncbi.nlm.nih.gov/pubmed/3193864

Likely explanations may be the power not measured by the rowing erg (e.g. body movement) and the long recovery time in a rowing stroke in which no power is generated.

Nice, thanks for the info!

Open access is imminent, unfortunately it probably won't help with older publications like this one. I do have a uni account though and will pull it there.

It doesn't take a rocket scientist to work out that the rower is very inefficient in generating power compared to a bike. Your body HATES high power out put to try and compensate for periods of zero power output, you can experience that on the rower by trying a fast pace at a low rating. Try rowing at 15spm and 2:00min pace if you can even achieve it, then simply free rate into the 20's and the difference is almost instantly obvious. Its like trying to go up a hill on a bike in the wrong gear, your heartrate will go through the roof.

This is the whole problem that Zwift needs to solve if rowers are going to be "Rowing" with the cyclists on a level playing field or else skirt round the problem by simply separating the results out into two categories.

The great thing about the rower is that your weight doesn't get entered as a factor when using RowPro online. As soon as you have a manual weight entry as part of the formula, its going to be subject to abuse.