Re: Consensus on Rohloff 14-speed hubs?

[carlfogel]

On 24 Apr 2006 12:17:01 -0700, carlfogel@comcast.net wrote:

>
>Alex Rodriguez wrote:
>> In article <T9SdndTK0pdfHNXZnZ2dnUVZ_sSdnZ2d@comcast.com>, haul_road@yahoo.com
>> says...
>> >
>> >
>> >They're a novelty but they don't work? Everybody would and should have them
>> >but they're too expensive? The coming thing? Not worth the weight? Good
>> >for some uses but not others?
>>
>> I've ridden these a couple of times for relatively short distances, less than
>> 10 miles. They worked fine and felt like they had less internal friction that
>> the Nexus hub I regularly ride. If they weren't so damn expensive, I would
>> probably have one of these on my commuter.
>> --------------
>> Alex
>
>Dear Alex,
>
>It's likely that differences in wind, road, and tires on the bike rides
>that you compared had more effect than any actual differences in
>transmission efficiency between the Shimano Nexus and the Rohloff hubs.
>
>When Kyle and Berto tested the efficiency of hub transmissions, those
>two models were virtually indistinguishable:
>
>http://www.ihpva.org/pubs/HP52.pdf
>
>See Figure 9, which graphs averaged efficiency through all gears, and
>Table 1, from which the figures were taken.
>
>Riders, of course, can't tell anything directly about internal friction
>losses. We can only notice misleading noises and estimate how fast
>we're going for whatever effort we think we're putting into gears that
>are probably different, while ignoring wind speeds, tire losses, and
>inflation differences.
>
>Even if we had duplicate bicycles, riders, and conditions, a 1% overall
>difference in hub efficiency (more than measured by Kyle and Berto for
>the Shimano and Rohloff hubs) would amount to only 18 seconds in 30
>minutes on a 10 mile ride at 20 mph.
>
>But I agree that two different [fill-in-the-blank]'s usually feel
>different whenever I compare them with the sensitive seat of my pants,
>even when I know that most of the feeling is actually in my head.
>
>Cheers,
>
>Carl Fogel

Horrors! I belatedly realized that I was exaggerating the
potential time difference due to a 1% transmission
efficiency difference at 20 mph for a 10 mile ride. It's not
even 18 seconds.

This calculator not only allows changing transmission
efficiency with lots of decimal places, but also
conveniently calculates times for distances:

http://w3.iac.net/~curta/bp/velocity/velocity.html

Put in 211.6 watts for the power to get 20 mph from the
defaults, including 95% efficiency, and put in 10 miles for
the distance--59.999 minutes.

Drop the efficiency to 94%, and the time changes to 60.2385
minutes, so 0.239 x 60 = only 14.3 seconds longer in a
half-hour ride, not the overblown 18 seconds that I
originally claimed.

The speed and time lost are less than 1% because a 1% power
change doesn't translate to a 1% speed change, since wind
drag and power required rise roughly with the cube of
velocity.

Of course, neither 14.3 nor 18 seconds is something that
we'd actually feel in a half-hour ride.

CF