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Old 09-08-2007, 09:56 AM   #1
Tim Donahey
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Post Understanding the Concept 2 Model B Drag Factor / Damper Settings

If you've used a Model B vs a Model C/D/E you've probably noticed that the same damper/drag factor setting for the one doesn't feel the same as the other. You're not crazy, this is because the Model B and the C/D/E use very different mechanisms for adjusting resistance.

If you look next to the fly wheel on a Model B, you'll notice two small wheels on the left side, and that your chain winds around one or the other. These are the cog wheels that offer different resistance levels. The larger one that is closer to the flywheel is a 15 tooth cog-wheel (15T) and the smaller one further away is a 13 tooth cog (13T). Switching the chain to the smaller cog offers greater resistance than the larger one. The Models C/D/E all use a singular 14 tooth cog (14T), so to find a comprable resistance level to a Model B requires a little recalculation.

(Note: Another alternative is to order a 14 tooth cog wheel from C2 that can be retrofitted onto your Model B. This will make the two essentially equal. Make sure to replace the chain at the same time to prevent skipping.)

The resistance is determined by cubing the number of teeth on the sprockets.

13 x 13 x 13 = 2197 (Model B, small wheel)
14 x 14 x 14 = 2744 (Models C/D/E)
15 x 15 x 15 = 3375 (Model B, big wheel)

For example, to convert a Model C's drag factor (DF) to an equivalent Model B (large cog) drag factor, first you would need to find the scale factor. This is done by, in the case of our example, dividing 14^3 by 15^3, or 2744/3375, equalling about .813. This is the number to divide your Model C's DF by to find the coorelating Model B DF.

So if I usually use a Model C with a drag factor of 120 and wanted to get the same level of resistance on a Model B (large cog) that I was using, I would do this:

120 (Model C 14T DF) / .813 (Scale Factor)= 148 (Equivalent Model B 15T DF)

And using the damper I would adjust the Model B to a DF of 148 to make it "feel" like the Model C @ 120.

(Note: To get a reading of the DF you'll need a PM2/PM2+/PM3/PM4 erg monitor)

Below are some tables for easy guestimating.

Model B/C/D/E Conversions
14T DF / .813 = 15T DF
14T DF / 1.249 = 13T DF
15T DF / 1.23 = 14T DF
13T DF / 0.80 = 14T DF

Recommended Drag Factor
............14T...15T...13T
250lbs - 139 – 171 - 111
200lbs – 132 - 162 - 107
175lbs - 125 – 154 - 100
150lbs - 120 – 148 - 96
125lbs – 114 – 140 - 91

Adjusting equivalent dampers from one model to the next isn't so exact, so take the following guide with a shaker of salt. Adjusting the drag factor is the best way to get a perfect fit, but if your Model B only has a PM1 monitor on it (and you can't evaluate the DF) the damper alone will get you within ball park.

Model C/D Damper.... Model B Damper................... Resistance
........1...................... large cog, speed ring.............. very light
........2...................... large cog, vents closed…......... light
.......2/3.................... large cog, ¼ open.................. light/medium
.......3/4.................... large cog, ½ open.................. medium
.......4/5.................... large cog, ¾ open.................. medium
.......5/6.................... large cog, vents open............. medium/heavy
........7............................... n/a............................. n/a
........8……….............. small cog, vents closed............ heavy
........9..................... small cog, ¼ open………….......... heavy
.......10.................... small cog, ½ open................... very heavy
.......n/a………............ small cog, ¾ open................... very very heavy
.......n/a………............ small cog, vents open.............. very crazy heavy

Recommended Damper Values
250lbs - 6-7
200lbs - 5-6
175lbs - 4-6
150lbs - 3-4
125lbs - 2-3

KEY
DF = Drag Factor
13T = 13 tooth cog wheel (Model B, small cog)
14T= 14 tooth cog wheel (Model C/D/E cog)
15T = 15 tooth cog wheel (Model B, large cog)

This is something that had perplexed me for quite awhile, so I hope this will help any of you out there with the same questions I once had.

Happy Rowing!
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Old 09-08-2007, 11:43 AM   #2
Tim Donahey
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Re: Understanding the Concept 2 Model B Drag Factor / Damper Settings

Here's an alternative table that could also apply to your erg:

Model C/D Damper.... Model B Damper................... Resistance
..........1/2................. large cog, speed ring............... very light
...........3................... large cog, vents closed……....... light
...........4................... large cog, ¼ open.................. light/medium
...........5................... large cog, ½ open.................. medium
...........6................... large cog, ¾ open.................. medium
...........7................... large cog, vents open............. medium/heavy
...........8………............ small cog, vents closed............ heavy
...........9.................. small cog, ¼ open………….......... heavy
..........10.................. small cog, ½ open.................. very heavy
..........n/a….............. small cog, ¾ open.................. very very heavy
..........n/a……............ small cog, vents open............. very crazy heavy




I can't really say which table is more accurate because DF will vary greatly depending on altitude, temperature, air circulation, and proximity to wallspace. For example the closer your erg is to a wall the lower the DF will become. Try it out.
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