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.