loss of power/energy with internal gear hub?
Roger
traditional chain/derailer setup for loss of energy due to friction or
other forces?
Or, given the same ratio (or gear) and same amount of power input,
which system translates more of that power into wheel spinning?
Thanks,
Roger.
Daniel Connelly
Whitt & Wilson discuss this.
Dan
Ted Bennett
The answer really depends on which gear you are in, for either system.
Efficiency for a clean, well lubricated derailleur system can be as high
as 98% if the chain runs straight, but it falls as low as under 90% with
more cross-chaining. Note that the ideal combination of cleanliness,
lubrication and straight run are only rarely present.
For internally geared hubs, chainline isn't (or shouldn't be) an issue,
but generally speaking the highest efficiency would be in direct drive,
that is, when power is not run through planetary gears with their
attendant friction. Rohloff claims efficiency of at least 95%, and both
SRAM-formerly-known-as-Sachs and Shimano are pretty evasive about their
worst-case efficiency specs. These efficiency figures are difficult to
verify because they are difficult to measure, but for a seat-of-the-pants
estimate, if such a hub feels at all warm after use, it sure isn't 97%
accurate.
Having 14 evenly spaced gears over a 6:1 range with a single shifter
would make an appealing alternative to a derailleur for many applications
except real racing. [But please note that I did not say I accept
Rohloff's claim as pure undisputed fact, nor would I ignore the higher
weight, high cost, limited torque rating, or other issues like shifting
performance, service or reliability - it's just about efficiency this
time, folks.]
It's also worth noting that the efficiency of a chain around a sprocket
falls off quite rapidly as you go smaller than 20 teeth, so bigger
sprockets are easily worth the small weight penalty.
Because cyclists have limited power, (some of us more than others:) ) and
these figures aren't easy to reliably measure, there's plenty of room for
argument about them, especially here on r.b.t.
Ted Bennett
Dave Balfour
Good luck
Dave Balfour
Bushnell IL
From: David Rodenhiser <dav...@scirocco.East.Sun.COM>
>I remember that some time in the last couple of years, someone posted
>on this list a chart detailing the efficiency of the Sachs 3 speed
>internal hub at various power levels. I can't seem to find it in
>my archives.
>Does anyone have a copy they could forward to me?
Hi David,
I guess this is what you are looking for:-
> Measurements of Efficiency of Chain and Shaft Drives
>
> Section 1.2.2
>
> Contributed by Chris Juden, CTC Technical Officer,
cyc...@ctc.org.uk
>
> The best work I know of on this subject was commissioned by Fichtel
&
> Sachs AG. Comparisons of single-speed,
> multi-speed hub and derailleur gearing were
> published in Radmarkt Nr.12/1983 and I am aware of other
> work within that company which compared the efficiency of chains in
> various states of neglect.
>
> Here's a summary of results, percentage efficiency values estimated
from
> the graphs printed in Radmarkt.
>
>
> New, clean, lubricated chain drives
> 1-spd 3-spd Hub Gear 6-spd Derailleur
> Power Low 1:1 High 24T 19T 13T
> 50W 96.0 90.6 93.4 87.3 94.2 94.1 92.1
> 100W 97.3 92.8 95.7 90.9 96.2 96.4 94.9
> 200W 98.1 94.0 96.9 92.9 97.4 97.6 96.9
> 400W 99.0 95.0 97.9 93.9 98.1 98.4 97.8
> Used chain (8000km), no rust, lubricated
> 100W 94-96%
> 200W 97-98%
> Neglected used chain (7000km), rusty, dry
> 100W 88%
> 200W 93%
>
> We can draw some interesting conclusions from these data.
>
> They confirm that hub gears are a little less efficient than
derailleur,
> even in direct drive, and show that they work better in low
> than high ratio.
>
> With a derailleur: running the chain around the little pulleys takes
> only about 1W. And a misaligned chain is much less wasteful
> than small sizes of the sprocket, especially at low power levels.
> Indeed: at 50W the out of line 24T does a bit better than the in
> line 19T! 13T is not even very small by today's standards, but is
> clearly rather inefficient. At very high power levels however,
> alignment may become as important as size.
Regards, Ian.
Ian Sims, GREENSPEED,
Recumbent Bikes, Trikes, & HPVs
69 Mountain Gate Drive, Ferntree Gully,
VIC 3156, AUSTRALIA
Phone +61 3 9758 5541, Fax +61 3 9752 4115.
Email i...@greenspeed.com.au
Web pages http://www.greenspeed.com.au
Roger wrote in message
<21ff2edc.0201...@posting.google.com>...
Roger
R.
antf...@hotmail.com (Roger) wrote in message news:<21ff2edc.0201...@posting.google.com>...
Paul Lawrence Hamilton
I've got a bike with a Nexus transmission. The effort and commute
time with this bike are about the same as with the hybrid it replaces.
The losses may be there, but are not significant from a riding
standpoint. The main difference between the two bikes is the smaller
gear range of the Nexus bike, which results in the lower "granny
range" being absent. One has to mash it more on steep hills. The
Rohloff would probably fix this with its wider gear range.
Paul
Paul Lawrence Hamilton, WWW.METROFLIGHT.W1.COM
Samis & Hamilton
Airport and Aviation Consultants
(301) 299-3573
Tom Ace
> Having 14 evenly spaced gears over a 6:1 range with a single shifter
The Rohloff hub's range isn't quite 6:1 (it's about 5.26:1).
> would make an appealing alternative to a derailleur for many applications
> except real racing. [But please note that I did not say I accept
> Rohloff's claim as pure undisputed fact, nor would I ignore the higher
> weight, high cost, limited torque rating, or other issues like shifting
> performance, service or reliability - it's just about efficiency this
> time, folks.]
Yes, the original question was about efficiency.
But in response to the points you list:
Weight isn't so horrible compared to all the parts it replaces.
And we know the significance of weight is overrated, yes?
Yes, the price is high.
The torque limitation isn't a problem. If you stay within the limits
Rohloff recommends, you can have a gear as low as a 22 front/32 rear.
How many riders need lower than that? In any case, if the hub is
suitable for tandem use as Rohloff says, I doubt you'd break it on
a single even if you ignored their recommendations.
Shifting performance is good. It shifts fast. And having 14 gears
available in sequence with one control is no small advantage; after
getting used to that, a front-and-rear-derailleur setup seems lame.
(Dished rear wheels seem lame now too.)
As far as reliability goes--I can't give a very meaningful report,
as I've had mine for less than a year. But so far it's been fine.
Tom Ace
Tim McNamara
Alex Moulton compared a 5 speed derailleur bike and a Sturmey-Archer 3
sp hub and found that the efficiency was very comparable. The results
are published in _Bicycling Science_ by Whitt and Wilson, IIRC. Doug
Milliken would know for sure.
alex wetmore
news:m2n0zoc...@localhost.bitstream.net:
A more up to date study was recently done by Frank Berto for Human Power
(the magazine of the IHPVA). Results aren't online that I'm aware of, but
the most efficient drivetrains were 3sp hubs. The 7sp Sachs internal gear
hubs and Rohloff were slightly less efficient than derailleurs.
alex
Edward Kleinbard
regard to the rohloff in particular.
Here's a web page that appears to be a scan of a chart from a test in
a German cycling magazine a few months ago:
http://www.selbst-machen.de/speedhub_vs_xt.gif
The chart compares a Rohloff 14 speed speedhub to a standard Shimano
XT setup. The bottom two plots on the chart just show the gearing,
using the left-hand vertical scale. All that they show is that the
magazine chose gearing on the XT setup that corresponded closely to
the Rohloff.
The top two plots are what you care about. They compare the relative
efficiency of the two systems at each comparable gear. The efficiency
("Wirkungsgrad") of the systems is expressed as a percentage, on the
right-hand scale. The red line is the Rohloff; the blue line is the
XT.
The different colored dots on the blue line just show which chainring
is being used (yellow= 22, green = 32, blue =44). So what you have is
a
direct comparison of the Rohloff to a conventional high-end derailleur
system used optimally (no hideously crossed chain).
For example, in 10th gear, the two systems have virtually identical
efficiencies of around 97%. The Rohloff's worst performance is in 5th
gear, where it is 2 percentage points worse than the derailleur
system;
its best is 9th gear, where it is 0.5% better in efficiency than a
derailleur.
Matt O'Toole
"alex wetmore" <al...@phred.org> wrote in message
news:a1ks9o$qjq$3...@216.39.149.189...
> A more up to date study was recently done by Frank Berto for Human Power
> (the magazine of the IHPVA). Results aren't online that I'm aware of, but
> the most efficient drivetrains were 3sp hubs. The 7sp Sachs internal gear
> hubs and Rohloff were slightly less efficient than derailleurs.
So the 3sp hubs were more efficient than derailer systems?
Matt O.
