Just did an hour row, why is my watts so much lower than my bike?

[frankencrank]

C2 did the best job ever in the way it measures the power,

My guess is this has nothing to do with the best way (it certainly isn't the most accurate way) but, rather, was the cheapest way.

[Carl Watts]

C2 did the best job ever in the way it measures the power,

My guess is this has nothing to do with the best way (it certainly isn't the most accurate way) but, rather, was the cheapest way.

Nope I think you totally missed the IP in the C2 rower monitor that makes it totally unique in the market. Its a bit of complex math that looks at the rotational inertia of the flywheel with a known mass and measures the acceleration and deceleration as well as the rpms to come up with a drag factor thats all used in a calc to produce the end power in Watts. Extremely smart and nobody else has been able to replicate it so that typically doesn't mean its the cheapest way, it tends to mean its the smartest way and one of the reasons your prepared to pay a premium for a C2 rower.

Hey look no offence, you may be great on a bike but there are some massive whirlpools your hitting in your rowing.

[frankencrank]

C2 did the best job ever in the way it measures the power,

My guess is this has nothing to do with the best way (it certainly isn't the most accurate way) but, rather, was the cheapest way.

Nope I think you totally missed the IP in the C2 rower monitor that makes it totally unique in the market. Its a bit of complex math that looks at the rotational inertia of the flywheel with a known mass and measures the acceleration and deceleration as well as the rpms to come up with a drag factor thats all used in a calc to produce the end power in Watts. Extremely smart and nobody else has been able to replicate it so that typically doesn't mean its the cheapest way, it tends to mean its the smartest way and one of the reasons your prepared to pay a premium for a C2 rower.

Hey look no offence, you may be great on a bike but there are some massive whirlpools your hitting in your rowing.

Why is inaccurate as to what the rower is actually doing at the handle best? Let me add, all this drag stuff should be easily calculated by examining the flywheel speed difference between the end of the power stroke and the catch, something easily known by the chain speed at those two times.

By this, I don't mean that what C2 does isn't useful. Repeatable is useful. But, the original question wass why does the C2 measure substantially lower than a bike in the same athlete. Part of that answer is where C2 measures the power.

[jamesg]

The main reason for power "losses" is changing body mass velocity on fixed rowergs. Unmeasured power of up to 50W is to be expected at very high ratings. On bikes only the leg cgs need move, so inertial loss is small.

At rowerg training ratings (around 20) there won't be much power loss, since only the pull is quick; so if we want to work efficiently, we just do it: low rating, full strokes. As most do.

Power losses are physical reality, so we can estimate them if we wish. The inertial loss noted above is the mass acceleration which necessarily happens before the chain can engage: if 1m/s, 80 kg, work done before every catch is ½*1²*80 = 40 J.

The fan braked flywheel and intermittent rowing action together allow flywheel speed measurement at every stroke and so an estimate of the power that keeps it spinning.

[johnlvs2run]

On rowing ergometers (at least the C2) power is measured at the fan

They did the same thing with the C2 bike.

I am blown away at the choices C2 made in measuring power. Accurately measuring the power would have been so easy

I completely agree.

[frankencrank]

The main reason for power "losses" is changing body mass velocity on fixed rowergs. Unmeasured power of up to 50W is to be expected at very high ratings. On bikes only the leg cgs need move, so inertial loss is small.

Actually, those losses can be quite large on a bike. While the masses are lower the legs are still quite massive and are cycling at a frequency much higher than the rower (plus the accelerations and decelerations occur twice per cycle) and when you combine this with the fact that the power loss varies with the cube of the cadence it doesn't take much to make those losses huge. My previous work suggests these losses are highly manipulatable and many can see large power increases (10% or so) by manipulating cycling cadence or stroke rate. viewtopic.php?f=3&t=200997

At rowerg training ratings (around 20) there won't be much power loss, since only the pull is quick; so if we want to work efficiently, we just do it: low rating, full strokes. As most do.

Agree that the losses are small at 20 SPM.

Power losses are physical reality, so we can estimate them if we wish. The inertial loss noted above is the mass acceleration which necessarily happens before the chain can engage: if 1m/s, 80 kg, work done before every catch is ½*1²*80 = 40 J.

You are calculating energy, not power. Power is the rate of using energy, (http://hyperphysics.phy-astr.gsu.edu/hbase/pow.html ) then you must average it over the cycle. Plus, body acceleration loss occurs twice per cycle, similar loss on the recovery also. At racing stroke rates those losses are much higher as the accelerations are higher and the frequency is higher. Because of this issue the increase in the loss tends to increase with the cube of the stroke rate.

The fan braked flywheel and intermittent rowing action together allow flywheel speed measurement at every stroke and so an estimate of the power that keeps it spinning.

True, The "problem" is it doesn't account for the shock cord losses so it doesn't accurately reflect what the rower is actually doing. So, while the C2 power is useful and reliable as a training tool (and to compare for competition) it underestimates athlete power compared to a typical bike power meter.

[frankencrank]

On rowing ergometers (at least the C2) power is measured at the fan

They did the same thing with the C2 bike.

I am blown away at the choices C2 made in measuring power. Accurately measuring the power would have been so easy

I completely agree.

I am not sure I understand how it works accurately on the bike. This method depends, it seems, on the cyclic application of power which allows them to to observe the acceleration of the fan (looking at the power application) and the deceleration (looking at the air pressure). On the bike, however, while there is a cyclic application, power application is never zero and the variation in power can be quite variable between people, varying between almost completely smooth to almost completely intermittent like the rower. That seems like a much tougher problem to me without measuring some strain also.

[jamesg]

The power absorbed by a fan is proportional to the cube of speed. Calibration, done by observing fan slowdown, provides the constant, aka drag factor.

[frankencrank]

The power absorbed by a fan is proportional to the cube of speed. Calibration, done by observing fan slowdown, provides the constant, aka drag factor.

Yes, that works on the rowing machine because the fan slows down when there is no power input so all the kinetics are known. but, on the bike, the power input is never zero. Therefore, there are a ton of variables affecting fan speed variation beyond the damper setting. I simply don't see how they can determine a power reasonably accurately looking at fan speed alone.

[johnlvs2run]

I simply don't see how they can determine a power reasonably accurately looking at fan speed alone.

They can't, and they didn't.

[frankencrank]

I simply don't see how they can determine a power reasonably accurately looking at fan speed alone.

They can't, and they didn't.

Then, what are they looking at?

[Rower-Cyclist]

Are there any rowers in here that can put out over 400 FTP or over 450 watts for 20 mins, on the bike, regardless of weight?

[Carl Watts]

Are there any rowers in here that can put out over 400 FTP or over 450 watts for 20 mins, on the bike, regardless of weight?

Even my best ever row was still sub 300W for the 5K which is closing in on 20 minutes at 17:49.0. Shows you how bad the "Direct Power" conversion is between the bike and the Erg.

Have thought about it for a long while now and its just not possible to come up with a conversion factor which probably explains why Zwift never tried to implement one.

[flatbread]

Are there any rowers in here that can put out over 400 FTP or over 450 watts for 20 mins, on the bike, regardless of weight?

why does it matter?

[Carl Watts]

Are there any rowers in here that can put out over 400 FTP or over 450 watts for 20 mins, on the bike, regardless of weight?

why does it matter?

Actually it matters. I was trying to compile some results to try and get a handle on the "Power conversion" between the Bike and the Rower a while ago and could not get a single reply.

If your trying to use the C2 Erg on Zwift then it would be really great to get a handle on it, but the only way to get a true result would be to train hard on both and then do your own math.