Model B and Model D drag

[Silverbk]

Hello all, new to the forum.

Rowed crew in high school and now using rowing to drop some weight and gain some fitness. I started on the model A in 1985, loved that machine, except moving it around.

I have a model B updated with PM5 and ergonomic handle.

I also have a Model D at work. I work on a tug boat so moving one machine around is not practical.

I would like to get both machines to "feel" roughly the same so I can better track my progress.

The pull seems harder on the B and I seem to finish 5K a bit faster but with less heart rate than on the D.

Is there a recommended way to adjust either machine?
Also getting a quick squeak at the finish on the B, I suspect its coming from underneath and not in the flywheel area.

Any help appreciated.

[Carl Watts]

Basically the answer is no.

You can upgrade the parts in a Model C to feel the same as a Model D but the Model B is simply to old and the design changed significantly with the Model C. The changes are visibly obvious.

The Model B is a museum piece now.

[Tsnor]

Tugboat? Nice. We get some pretty big wakes off tugboat/barges on the Hudson.

What does the PM5 report for Drag Factor on the Model B ? If its something reasonable you should be able to set the same drag factor on the model D. That will get you closer to the same feel.

Also, the model B has two different chain sprockets (one 13-tooth, one 15-tooth). Switching the chain should give you a different feel - more teeth is a lighter pull.

For tracking progress you should be able to just compare watts/splits/etc. No one has reported any ranking advantage for or against a model B, and records are not kept separately for the different rowers. AFAIK the same reported work done on model B and D is the same actual work done.

re "The pull seems harder on the B and I seem to finish 5K a bit faster but with less heart rate than on the D." Pull seems harder could be a higher drag factor on the B than the D. (Depending on how long since the screen on the model D has been cleaned the drag factor may be very low on the D - how much maintenance does an erg get on a tug boat?). For the "faster but with less heart rate" you may be a more efficient rower at a higher drag factor. Or there could be some other environmental difference (amount of sleep, ambient temp, etc). Either way, if you are "faster but with less heart rate" then you are doing more work with less effort.

re: "Also getting a quick squeak at the finish on the B, I suspect its coming from underneath and not in the flywheel area." No clue. Maybe see if this helps https://www.concept2.com/service/indoor ... e-monorail or check foot stretchers for loose hardware. https://www.concept2.com/files/pdf/us/i ... cement.pdf or maybe seat ?

[Cyclist2]

I still row my "museum piece", Carl. It, like all C2 machines is great (except for the noise). My PM2 still works just fine, too.

Here is a drag comparison for the various machines. A speed ring on the B is to block more air coming in. I made one myself out of light plywood, people have used other things from roofing paper to inner tubes. The feel of the two is different, as expected, but you can get the drag factors close.

https://www.concept2.com/files/pdf/us/i ... arison.pdf

[Nomath]

Although the flywheel cage of the model B looks quite different, this is only a cosmetic aspect. Both model B and model D are air-braked ergometers and follow the same physical equation : dω/dt = (P/(J*ω) - C/J * ω²) .
ω is the angular speed of the flywheel ; P is the momentary power input by the rower, C is the drag coefficient ; J is the moment of inertia of the flywheel.
Although Concept2 is rather secretive about the exact value of the moment of inertia, it is pretty sure that it is the same for model B and D, and equals 0.100 kg m². Without power input, thus in the recovery phase, model B and D behave identical if the drag factors are the same. The flywheel speed drops at the same rate in both models.

However, there is a difference during the drive phase. Power is the product of handle speed vh and force F applied to the handle: P = vh * F. If the clutch is engaged, the handle speed is always proportional to the rotation speed of the flywheel: vh = k*ω , where k is the gearing constant. So for the drive phase the above equation becomes : dω/dt = (F*k/J - C/J * ω²)
The value of k is determined by the chain pitch and the size of the sprocket wheel. The model D sprocket wheel has 14 teeth, whereas model B has a choice between 13T and 15T. To my knowledge the chain pitch of both models is the same : 1/4 in = 0.635 cm. So the gearing constant for the model D is: 2π *100/(14*0.635) = 70.7 radians/m, whereas for model B there is a choice between k(13T) = 76.1 and k(15T) = 66.0. This implies that on the model B you have a choice between pulling a bit faster on the 15T cog with a lower force or pulling a bit slower with a higher force on the 13T cog (compared to a model D). Because, for a certain cog, force goes up quadratic with speed, this means a choice between a force about 16% higher for 8% reduction in speed, or 16% lower force with an increase of 8% in speed. There is no way that you can pull with the same resistance feel on a model B compared to model D, at the same drag factor.

I read an old post on a different forum where someone explained that you could adjust the drag factor on a model B to get the same resistance feel as on a model D. For example, using the 15T cog, the drag factor should be set to 148 instead of 120. However, this will mean that the flywheel loses speed more quickly in the recovery. This is a nice example where a computer simulation may help to understand the differences. If I find some time, I will try to compare these different settings of drag and cog size in a simulation run.

Both model B and model D are true ergometers, meaning that they do an accurate measurement of the work in a stroke and the power input by the rower. Model D uses 6 magnets on the flywheel compared to 3 on a model B. That means that the power measurement on a model D is more precise, but not more accurate. If you are not familiar with the distinctions between these terms in science and technology, the picture below taken from Wikipedia may give a clue. Another analogy : model B is a like an accurate scale with 0.5 kg resolution whereas model D is an accurate scale with 0.2 kg resolution.

[Silverbk]

I'm captain on the Navigator. We do about 20 trips a year to Albany so you have probably experienced my wake.

I rowed on the Hudson for FDR back in the day.

Tugboat? Nice. We get some pretty big wakes off tugboat/barges on the Hudson.

What does the PM5 report for Drag Factor on the Model B ? If its something reasonable you should be able to set the same drag factor on the model D. That will get you closer to the same feel.

Also, the model B has two different chain sprockets (one 13-tooth, one 15-tooth). Switching the chain should give you a different feel - more teeth is a lighter pull.

For tracking progress you should be able to just compare watts/splits/etc. No one has reported any ranking advantage for or against a model B, and records are not kept separately for the different rowers. AFAIK the same reported work done on model B and D is the same actual work done.

re "The pull seems harder on the B and I seem to finish 5K a bit faster but with less heart rate than on the D." Pull seems harder could be a higher drag factor on the B than the D. (Depending on how long since the screen on the model D has been cleaned the drag factor may be very low on the D - how much maintenance does an erg get on a tug boat?). For the "faster but with less heart rate" you may be a more efficient rower at a higher drag factor. Or there could be some other environmental difference (amount of sleep, ambient temp, etc). Either way, if you are "faster but with less heart rate" then you are doing more work with less effort.

re: "Also getting a quick squeak at the finish on the B, I suspect its coming from underneath and not in the flywheel area." No clue. Maybe see if this helps https://www.concept2.com/service/indoor ... e-monorail or check foot stretchers for loose hardware. https://www.concept2.com/files/pdf/us/i ... cement.pdf or maybe seat ?

[jag]

I’ve owned all models, A through E (currently using an E). You want to purchase a Model B speedring (also called wind damper extension ring) for your B from C2 support. Very easy to install using instructions https://www.concept2.com/files/pdf/us/i ... nstall.pdf. Then use this table to adjust your B for comparable performance using this https://www.concept2.com/files/pdf/us/i ... arison.pdf

You can achieve similar result by arranging a towel over part of the B, but the speedring is calibrated and not subject to falling off. It is as well designed as the B itself and works great.

The feel is somewhat different even at the same drag factor (which you can read on your PM to make final adjustments). The B simply feels more solid, especially at the catch. But exercise is the same and both actually feel great, just a little different.

[Tsnor]

I'm captain on the Navigator. We do about 20 trips a year to Albany so you have probably experienced my wake.

I rowed on the Hudson for FDR back in the day.

Small World! I row out of the HRRA boat house near Pok. FDR rows out of the same boathouse.

[haus]

I still have the B I bought new in 1993 (museum piece! Carl, you're making me feel old haha!), but I'm using a decently-upgraded C these days. Does anyone remember that (I think) in addition to the speed ring, C2 once offered a 14T sprocket for the B that replaced the dual sprocket (13T/15T) and made the gearing feel more like the later models, or am I imagining that?

I miss the sound of the B. It is unique and beastly, in a good way, but the family doesn't like it. Ultimately, as others have said, it'll never feel anything like one of the later models.

[johnlvs2run]

I would like to get both machines to "feel" roughly the same so I can better track my progress.

Covering the cage with roofing paper or truck tire innertube attached with zip ties works great for lowering the drag factor and reducing the noise. I also attached a wood arm to the cage to extend the monitor.

The drag factor will be different, unless you replace the 13 and 15 tooth cogs with a 14 tooth cog, but you can get the same resistance and feel.