Bearing drag accounted for by the Concept2 PM

[lazy_rower]

I just ordered a drive train upgrade (PN 1915) for my Concept2 model C, and am anxiously awaiting its arrival. Looking at the assembly instructions, I'm questioning my understanding of what sources of drag are accounted for by the performance monitor.

My (new) understanding is that the axle sits on bearings connected to the rower frame. The sprocket for the chain screws onto the axle. The flywheel spins on the axle via the clutch assembly with a 1 way bearing.

The PM calculates the drag factor based on the deceleration of the flywheel when the flywheel is freespinning (when you're not pulling or are pulling slower than the flywheel is spinning). In that case, the only bearing drag included in the calculation is from the clutch bearings. When you're pulling, the clutch is engaged, and the axle bearings are spinning instead of the clutch bearings.

One a well maintained unit, I would assume that the difference is negligible. On an older, less maintained, somewhat gummed up, unit, could this difference be meaningful, depending on which bearings are more gummed up?

I ask because my machine always feels harder to pull for the same drag factor than the machines at my local Y and local rowing club. I'm very curious to see whether the drive train upgrade changes this. (And yes, I am familiar with arguments around the shock cord. Please don't go there.)

[Sakly]

(And yes, I am familiar with arguments around the shock cord. Please don't go there.)

Just a guess - I think the mentioned possible shock cord differences have higher influence.

[JaapvanE]

The PM calculates the drag factor based on the deceleration of the flywheel when the flywheel is freespinning (when you're not pulling or are pulling slower than the flywheel is spinning). In that case, the only bearing drag included in the calculation is from the clutch bearings.

That is correct.

One a well maintained unit, I would assume that the difference is negligible. On an older, less maintained, somewhat gummed up, unit, could this difference be meaningful, depending on which bearings are more gummed up?

Mechanically, it is quite an extensive mechanism with several bearing and chains. Aside bearings running less optimal, chain stiffness is also a thing (especially given the several 180 degree turns). Sprocket alignment can have a big effect as well.

I ask because my machine always feels harder to pull for the same drag factor than the machines at my local Y and local rowing club. I'm very curious to see whether the drive train upgrade changes this. (And yes, I am familiar with arguments around the shock cord. Please don't go there.)

I work a lot with mechanical systems, and you see that these machines have to settle in, similar to a new car. Alignment etc. never is 100% perfect, but using the machine but not go all-out from day one allows sprockets etc. to settle in without damage. And some machines just see a lot of abuse and neglect. No oil for decades makes bearings and chains stiff, and thus make you spend a lot of energy that isn't measured.

An additional one is levelling: in my local gym they raised the front feet 2cm, which makes recovery really a struggle for me. That kind of you feel as well.

[Carl Watts]

Any extra drag in the three internal flywheel bearings will just show up in the drag factor calculation and will be cancelled out.

Things that will stack up against you as true loses will be the things like chain friction, seat roller bearings, crap on the slide, the two chain guide plain bearings in the frame, the bearings in the shock cord pully flywheels, the two bearings that support the flywheel. Its my belief that the correct tension of a new shock cord actually helps your performance, your muscles used on the drive are far more efficient than those used on the recovery so the 90% of stored energy in the cord that's put in on the drive comes back to assists you on the recovery.

On the Drive, all the internal bearings in the flywheel are stationary as they are moving with the drive shaft, its only on the recovery do they spin and this cycle of the movement is used to calculate the drag factor as the flywheel decelerates.

[jamesg]

my machine always feels harder to pull for the same drag factor than the machines at my local Y and local rowing club

Maybe you bike to site and are warm when you get arowing.

My machine always feels hard to pull when I get on it. As I warm up, it gets far easier; maybe it's just warmer blood flows easier than cold, or I self anaesthetize somehow: endorphins? Not a great worry in any case.

[lazy_rower]

my machine always feels harder to pull for the same drag factor than the machines at my local Y and local rowing club

Maybe you bike to site and are warm when you get arowing.

Sadly, I'm never warmed up before I get to the erg. Would love to have a good bikeable path to the gym, but it's never been the case. I do believe that my machine is mechanically just a bit stiffer than others. Tonight I'm changing out everything but the flywheel. We'll see how that changes things.

[Tsnor]

Tonight I'm changing out everything but the flywheel. We'll see how that changes things.

Do you use a HR monitor? At a wild guess based on bike chains, you can see 3% or so improvement in unmeasured drivetrain drag, so 5 watts or so. This might be in the range of showing up in steady state as reduced HR at the same load or improved split at constant HR.....

Be very interested in your subjective report (noise, vibration, power, etc.) and in any objective measurements you can grab. When you clean that flywheel do reset your drag where you want it.

ASIDE: I saw the "Concept2 Drive Chain Assembly 1915" for $99USD in the concept2 amazon store and the same thing for $47.85USD plus shipping on the concept2 website. No idea why the price is so different.

[lazy_rower]

Do you use a HR monitor? At a wild guess based on bike chains, you can see 3% or so improvement in unmeasured drivetrain drag, so 5 watts or so. This might be in the range of showing up in steady state as reduced HR at the same load or improved split at constant HR.....

Be very interested in your subjective report (noise, vibration, power, etc.) and in any objective measurements you can grab. When you clean that flywheel do reset your drag where you want it.

ASIDE: I saw the "Concept2 Drive Chain Assembly 1915" for $99USD in the concept2 amazon store and the same thing for $47.85USD plus shipping on the concept2 website. No idea why the price is so different.

I do use a heart rate monitor, and anecdotally, I get worse performance for the same heart rate on my home erg. Of course, I haven't done a careful comparison.

I'd bet that the Amazon store is some random reseller pocketing $40 profit and drop shipping parts from Concept2.

[lazy_rower]

I swapped out the axle, sprocket, axle bearings, idler pulleys, and shock cord. I also oiled the flywheel. It took about an hour, because I was learning about the erg assembly as I went, and the instructions didn't always cover the Model C.

The upgraded erg is completely different. Of course, I didn't have enough time this evening to really test it, but it pulls easier and is much quieter. Flywheel air movement is now the dominant noise. If I were to guess by feel, the reduced effort is the difference between a 2:15 and 2:20 warmup pace. Really that much.

The bad news is that my flywheel bearings are going. They're not bad, but they're lightly grinding, even with a quick cleaning and some oil. With the chain out, I can spin the sprocket by hand, and it's completely silent. The moment I stop the sprocket, the flywheel bearings start grinding.

[Carl Watts]

The moment I stop the sprocket, the flywheel bearings start grinding.

I ended up modifying mine in the end, removed the inside shields of the two bearings, cleaned and just oiled them.

The one way bearing / clutch bearing is best just lubed with a clear synthetic grease like Super Lube, its just the right viscosity, not too thick to hamper the roller bearing movement in and out of the cam and not to thin to spray out all over the flywheel due to centrifugal force.

[nick rockliff]

I swapped out the axle, sprocket, axle bearings, idler pulleys, and shock cord. I also oiled the flywheel. It took about an hour, because I was learning about the erg assembly as I went, and the instructions didn't always cover the Model C.

The upgraded erg is completely different. Of course, I didn't have enough time this evening to really test it, but it pulls easier and is much quieter. Flywheel air movement is now the dominant noise. If I were to guess by feel, the reduced effort is the difference between a 2:15 and 2:20 warmup pace. Really that much.

The bad news is that my flywheel bearings are going. They're not bad, but they're lightly grinding, even with a quick cleaning and some oil. With the chain out, I can spin the sprocket by hand, and it's completely silent. The moment I stop the sprocket, the flywheel bearings start grinding.

Not quite sure what you mean by flywheel bearings. There is only a single one why clutch bearing in the flywheel?

[lazy_rower]

Not quite sure what you mean by flywheel bearings. There is only a single one why clutch bearing in the flywheel?

The flywheel has a one-way roller bearing, to act as a clutch, and two ball bearings held in by a split ring for stability.

I just removed the ball bearings, cleaned, and oiled them. I wouldn't say the flywheel noise is changed, but I have a working drag factor range of 95 to 214 with the damper. The flywheel spins for about 90 seconds if I let it freewheel. That seems good enough.