Single stage direct, single stage compound, two-stage epicyclics


bertin753
 

I'm reading up on the differences, but quick question: Am I right in thinking that the first type (eg TF hub) has least drag, the second (AM, TC) somewhat more, and the third (FM?) the most?

Second question: Direct is the most efficient gear, right? But with single stage and s-s-compounds, is the added drag in over and under drive gears significant?

I can't notice more drag in 3d than in 2nd on my AM hub, tho' perhaps a wee bit in first. I did notice drag on a new S3X hub in first.



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Patrick Moore
Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum


Michael Wilson
 

I do not have a mental model that predicts that an KS/KSW/TC/AM/FW/S5 style planet pinion would be lower efficiency than the single-sized planet pinion of the K/TF/AW etc.  Maybe the offset loads on the pinion pin add friction?  With the S5 the extra rotating sun in principle adds friction.

My Butt-Drag-Detector (similar to my butt-dyno in a car) is poor enough that it cannot be trusted.  It tells me that all low gears are inefficient on any bike, including derailleurs, although it usually complains less about the derailleurs.  As my power declines, my BDD complains more because it does not know my power has declined; it assumes that the loss of speed is from the machine.

My Butt-Drag-Detector also contradicts some measured efficiency numbers.  The Rohloff measures to be quite efficient, but my BDD says otherwise.  I believe my BDD is mostly a pedal-response detector, not an actual drag detector, so if there is a lot of internal slop the pedal response is slow and the BDD registers that as inefficiency.  Which it could be with an imperfect pedal stroke, as opposed to the efficiency measurements using a constant-velocity electric motor.  Also I believe the Rohloff measured best efficiency was one gear different than direct, and nobody could explain why.

That said, making my BDD happy is important in making the bike ride more fun, so the Rohloff bike almost never gets ridden.


bertin753
 

Interesting, and more or less agrees with my own experience -- not the Rohloff, I haven't ridden one, I mean first gears in 3 speed hubs seem more draggy.

I've been tempted to buy a Rohloff, but observations like yours, as well as several hub gear drag tests saying that Rohloff's drag is more than they advertise, have made me wary. 2 and 3 speeds for me, please.

Rode the AM bike the other day, worrying about drag. It felt fast on that day! I gear it so that high/third is my cruising gear, and really, can't say that I feel more drag in 3d than in direct/second. First -- jury out.

On Fri, Mar 4, 2022 at 9:28 AM Michael Wilson <mtwils@...> wrote:
I do not have a mental model that predicts that an KS/KSW/TC/AM/FW/S5 style planet pinion would be lower efficiency than the single-sized planet pinion of the K/TF/AW etc.  Maybe the offset loads on the pinion pin add friction?  With the S5 the extra rotating sun in principle adds friction.

My Butt-Drag-Detector (similar to my butt-dyno in a car) is poor enough that it cannot be trusted.  It tells me that all low gears are inefficient on any bike, including derailleurs, although it usually complains less about the derailleurs.  As my power declines, my BDD complains more because it does not know my power has declined; it assumes that the loss of speed is from the machine.

My Butt-Drag-Detector also contradicts some measured efficiency numbers.  The Rohloff measures to be quite efficient, but my BDD says otherwise.  I believe my BDD is mostly a pedal-response detector, not an actual drag detector, so if there is a lot of internal slop the pedal response is slow and the BDD registers that as inefficiency.  Which it could be with an imperfect pedal stroke, as opposed to the efficiency measurements using a constant-velocity electric motor.  Also I believe the Rohloff measured best efficiency was one gear different than direct, and nobody could explain why.

That said, making my BDD happy is important in making the bike ride more fun, so the Rohloff bike almost never gets ridden.



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Patrick Moore
Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum


John S. Allen
 

Simplifying somewhat, drag has two components, one which is constant, the other in proportion to load. The Rohloff manufacturer's testing was under heavy load, increasing efficiency. An unbiased report on the Rohloff's and many other IG hubs' efficiency may be found here:

http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf

On 3/5/2022 6:43 PM, bertin753 wrote:
Interesting, and more or less agrees with my own experience -- not the Rohloff, I haven't ridden one, I mean first gears in 3 speed hubs seem more draggy.

I've been tempted to buy a Rohloff, but observations like yours, as well as several hub gear drag tests saying that Rohloff's drag is more than they advertise, have made me wary. 2 and 3 speeds for me, please.
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John S. Allen

CyclingSavvy Instructor
League Cycling instructor
Author, Bicycling Street Smarts
Technical Writer and Editor, sheldonbrown.com
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bertin753
 

That's the old standby. Others have done similar studies over the years with slightly varying results, but the upshot is that the simpler hub gears at least are pretty close in efficiency to derailleur systems. And I suppose that a % up or down isn't going to affect one's everyday riding, though it does incline me to keep to the simpler SA hub systems.


On Sun, Mar 6, 2022 at 1:52 PM John S. Allen <jsallen@...> wrote:
Simplifying somewhat, drag has two components, one which is constant,
the other in proportion to load. The Rohloff manufacturer's testing was
under heavy load, increasing efficiency. An unbiased report on the
Rohloff's and many other IG hubs' efficiency may be found here:

http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf


On 3/5/2022 6:43 PM, bertin753 wrote:
> Interesting, and more or less agrees with my own experience -- not the
> Rohloff, I haven't ridden one, I mean first gears in 3 speed hubs seem
> more draggy.
>
> I've been tempted to buy a Rohloff, but observations like yours, as
> well as several hub gear drag tests saying that Rohloff's drag is more
> than they advertise, have made me wary. 2 and 3 speeds for me, please.
>

--
John S. Allen

CyclingSavvy Instructor
League Cycling instructor
Author, Bicycling Street Smarts
Technical Writer and Editor, sheldonbrown.com


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Patrick Moore
Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum