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Power loss with Rohloff

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lewis noble:
Spent two weeks on the cycle trails in Burgundy in September - superb cycling, lovely weather and scenery . . .

Enough of that.  One of the most common questions I was asked when my Raven Tour was parked up was about power loss compared with a derraillieur.  Has anyone researched this??

My impression is that there is minimal / nil loss in gears 8 - 14, harder to quantify in gears 1 - 7; it feels as though there is some loss but perceptions can be unreliable.

I do remember seeing some test results about this, which suggested that the power loss is perhaps greater than in a perfectly set up derraillier gear, but no more than real world results on a bike in regular use.  Can anyone recall this / remind me??

Lewis - Sheffield

geocycle:
Hi lewis,
hope you enjoyed France!

You raise an interesting and hotly contested point!  Rohloff published the following paper on the efficiency of speedhubs in response to an article by Kyle and Berto which suggested hub gears (all) were about 2% less efficient than (clean) derailleurs:  http://www.ihpva.org/HParchive/PDF/hp55/hp55p11-15.pdf.

Efficiency (%) (K+B)
Derailleurs 87-97
Gear Hubs 86-95
Note: Test performed with 80W, 150W, 200W input.
 
Rohloff's article shows how complex it is to measure!  Figure 5 is interesting, to my eye it demonstrates better results for the direct drive gear 11 relative to a derailleur but inferior performance in gears 1-3, with the rest being broadly equivalent.  The original authors stand by their results but acknowledge the quality of the rohloff.

NB These data are collected in experimental conditions and we can all make our own mind up on how the real world will change the findings.  Riding style and the extent which derailleurs are kept clean will be very important to efficiency.

freddered:
You just can't imagine the noise I hear from some derailleur systems when I ride Audax.  The clunking and grinding in extreme gears, the occasional preson trying to unjam their chain from the BB (as it fell off trying to change from 24th gear to 1st at the start of a sudden climb).

I absolutely swear that my Rohloff hasn't slipped or missed a change in 8000 miles.

I have a timed 14 mile route and their is no measurable difference between my Rohloff and my derailleur bike.

Derailleur Jockey Wheels can be very stiff without you realising so I reckon efficiency is about the same as a 'real world' derailleur.

bike_the_planet:
The actual amount of power loss is minimal.

There are 2 sorts of losses in hub gears such as a Rohloff.

1) Friction due to oil seals. This is a constant value regardless of load or speed. It is the reason that your cranks tend to rotate when you push your bike along the ground whilst walking alongside.

2) Friction due to gear meshing. This is a variable value and depends on load (ie power you are tansmitting to the wheel). The more power you transmit, ie the harder you pedal, the more loss

In a hub such as a Shimano Nexus which uses grease instead of an oil bath, the losses as described in 1) are less than a Rohloff, but there is correspondingly more loss as described in 2).

I have seen the figures for Rohloff and it has the lowest losses for any epicyclic gear system but marginally higher than a derailleur assuming the latter is clean and in good working order.

Regards,

Tony

lewis noble:
Thanks for these observations.

The conclusions match my own observations, that perceived losses seem higher when really heaving on the pedals - not good practice anyway, and I much prefer trundling along gently . . . .  people pass me, but I often catch them up.

Best wishes to all

Lewis - Sheffield

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