Bicycle Mechanics - Rohloff hubs: lowered efficiency negligible or non-negligible?

There are charts somewhere on the web that show the efficiency losses of the Rohloffs, compared with derailleurs, for each gear.

For racing, it could be a very legitimate concern. But in other cases -- when you aren't very pressed for time, or trying to keep up with fast riders, or in some other situation where two or three or four percent losses might matter -- it may or may not be significant.

One percent seems pretty minor. Two percent also seems minor. But when you get up around three or four percent, it starts to make one wonder.

Then again, maybe it doesn't really matter.

If anyone has any viewpoints or perspectives on this, please feel free to post them.

It only matters if you're riding at LT and time-trialing on all your rides and giving it your all. Otherwise, if you can just push 2-4% harder when using the Rohloff hub.

it depends


mountain bike racing, negligible

road racing, noticeable

It only matters if you're riding at LT and time-trialing on all your rides and giving it your all. Otherwise, if you can just push 2-4% harder when using the Rohloff hub.

The Rohloff has less transmission efficiency than 2-4%. There was a scientific paper published on Human Power a while ago, and the Rohloff was tested, among other gear hubs and derailleurs. The best transfer efficiency the Rohloff achieved was about 5%, but usually a bit less.

The gear hubs with best transfer efficiency were the 3-speed Shimano gear hubs, around 4-5%. Where the EFF did I save that .pdf....

I couldn't find the original paper, but I did find a shorter one, that, too, on Human Power, as an answer to Rohloff. This is what the paper concludes:



To summarize, we are reasonably
confident that the rank order between
transmission efficiencies that we found
would not change appreciably as load is
varied within a normal range. In other
words, transmissions should rank about
the same at either low or high loads. We
feel that the loads we tested under are
typical of the actual conditions under
which hub gears are used and represent a
reasonable average efficiency. In our article
we therefore concluded that hub
gears are about 2% less efficient that derailleur
transmissions under typical field
conditions. We see no reason to change
that conclusion.

A Rohloff will never be in my budget, but if I were...
I'd optimize the chain ring/cog ratio to use 11th gear as much as possible, since it's direct drive.

One percent seems pretty minor. Two percent also seems minor. But when you get up around three or four percent, it starts to make one wonder.

Then again, maybe it doesn't really matter.

Suppose you had a commute that takes you exactly 30 minutes with whatever you're using as a base line drive train. A drive line that's 4% less efficient would take you 31 minutes and 12 seconds. Would that bother you? I rather suspect that would drop out into the background noise of weather and traffic conditions. In other words, the normal day-to-day variation in commuting times would exceed any difference that could be attributed to the hub.

Suppose you had a commute that takes you exactly 30 minutes with whatever you're using as a base line drive train. A drive line that's 4% less efficient would take you 31 minutes and 12 seconds.

Uh, it doesn't work that way. 4% drivetrain efficiency loss does not equate to 4% time gain.

Uh, it doesn't work that way. 4% drivetrain efficiency loss does not equate to 4% time gain.

So how does it work?

One question that I never seem to find an answer for in these tests of internal geared hubs; is the mechanical efficiency number given for the hub just for the hub or for the entire drivetrain?

Remember, an internal geared hub still has to use a chain,chainring and rear cog so is the "95%" (or whatever number is quoted) efficiency value just for the hub itself or does it include the rest of the required drivetrain parts too?

Uh, it doesn't work that way. 4% drivetrain efficiency loss does not equate to 4% time gain.

So what is the difference likely to be? I notice that you left out the pertinent point. That being that the difference, whatever it is, is likely to less than normal day-to-day variations.

So what is the difference likely to be? I notice that you left out the pertinent point. That being that the difference, whatever it is, is likely to less than normal day-to-day variations.

Someone posted these efficiency test results over on wreck bicycles.tech some time ago. I seem to remember that the Rohloff did not fare as favorably against derailleur systems as some of the other gearhubs, but there are a few things to consider. The Rohloff is currently the only gearhub that is oil bath lubricated, and must necessarily use seals. In my own experience, these seals do create some drag (which I really only notice in the work stand) which does decrease with use.
Even so, if I recall correctly, the Rohloff came in somewhere around 94% efficient, which is slightly less than Rohloff's own claim of 96% efficiency. The overall efficiency will be an average over all gears, as it will vary depending on how many steps of gearing the power flow follows in any particular gear. Optimal efficiency, we would expect, should be acheived in direct gear.
Derailleur gearing efficiency will vary as well any time an absolutely straight chain line is deviated from.
Speaking as someone who does not, nor never has ridden competitively, nor do I track time/distace or anything like that, I did not notice an appreciable difference in drag with my own Rohloff over the XT/XTR drivetrain it replaced. I do however appreciate the ability to grab as many gears as I want or need, up or down, instaneously, whether the pedals are turning or not.

So how does it work?

Think of it this way. If you decreased the wattage you produced into the bike by 4% do you go 4% slower? If you increased your wattage by 4%, do you go 4% faster?


So what is the difference likely to be? I notice that you left out the pertinent point. That being that the difference, whatever it is, is likely to less than normal day-to-day variations.

The difference to the user is negligible. Once you are riding internally geared hubs like that I don't think you'll be trying to set any TT or climbing records at your local club rides.

When I was a kid, I had a bike with a generator lighting system where the generator rolled on the side of the tire. When I used the generator I felt like I was going nowhere fast and I only used the generator when going down hill and when I had to have a light. I am guessing that the generator was probably about a 3 to 5 watt drag on my engine. So this should compair with the loses in the hub. If you put a generator light system on your bike and ride you should be able to decide if the hub is right for you.

When I was a kid, I had a bike with a generator lighting system where the generator rolled on the side of the tire. When I used the generator I felt like I was going nowhere fast and I only used the generator when going down hill and when I had to have a light. I am guessing that the generator was probably about a 3 to 5 watt drag on my engine. So this should compair with the loses in the hub. If you put a generator light system on your bike and ride you should be able to decide if the hub is right for you.

This is a bad comparison. The tirewall rub generator is consuming much more than 3-5w to produce 3-5w of power. Having ridden both rohloff and a sidewall tire generator, the latter IS going to be noticeable. The rohloff is like riding any other internally geared hub (sturmery archer etc.).

Maybe someone will do a study where they compare how many watts somebody is losing through the rohloff hub vs a derailleur system. I doubt the loss will be meaningful to anyone who actually rides these.

I just built up an old Trek Steel tour bike with a Nexus red band hub. I don't notice any difference. I am sure there must be a slight difference, but I do not notice it when riding.

I do notice a big difference when I have to pick up the bike. It is much heavier in the rear end.

Kyle & Berto article about transmission losses etc. (plus other interesting articles)

http://www.ihpva.org/pubs/HP52.pdf


Rohloff's answer to Kyle & Berto article

http://www.ihpva.org/HParchive/PDF/hp55/hp55p11-15.pdf



Here is Rohloff's own article about transmission efficiency

http://www.rohloff.de/en/technical/speedhub/efficiency/

Also remember that the measured 3 to 4% difference is under laboratory conditions. Since I rarely ride in a laboratory I think it may not be applicable. I'd like to see a comparison done with a chain at 0.5% stretch, add some dirt, leaves, and grass clippings and use an eye dropper with a saline solution, a single drop on the chain every minute would do nicely.

When I was a kid, I had a bike with a generator lighting system where the generator rolled on the side of the tire. When I used the generator I felt like I was going nowhere fast and I only used the generator when going down hill and when I had to have a light. I am guessing that the generator was probably about a 3 to 5 watt drag on my engine. So this should compair with the loses in the hub. If you put a generator light system on your bike and ride you should be able to decide if the hub is right for you.I agree with operator, you are guessing wrong. I have a B&M bottle dynamo on my winter bike, and the losses from that are far worse than any transmission inefficiency I've ever experienced. Well, maybe a broken spoke and resulting brake drag are worse.

Top notch hub dynamos would give a more realistic comparison. The SON dynamo for example operates somewhere around 5 watt loss range when switched on. When switched off, the SON claims a 0,5W loss or so.

--J

Thanks it is good to know that the sidewall generator system eats up more than 5 watts. If there are any trainers with power meters, then maybe a person could ride at 100 watts for a while and then go to 105 watts and see the precieved difference in the effort required. Going back and forth between the power levels over a period of an hour or two should be helpful. I am not sure but I think that I would notice the difference. But if a person jumped on the trainer and rode for an hour without looking at the power meter they probably could not tell if it was set to 100 watts or 105 watts. But then again I really don't know because I don't have any way to test my guesses.

A couple of percent diff in drivetrain efficiency is going to make almost no difference to riding speed. You have to recalculate the difference in total drag, and the drivetrain drag is only a small proportion of the total. Imagine you're riding a road bike at about 16mph. That takes about 150Watts. Most of the 150Watts is consumed fighting the air. Some on rolling resistance. A few watts are lost to the drivechain, say its 10W (I'd be surprised if it's this high). 4% of 10W = 0.4W, so a 4% difference in drivetrain efficiency is only going use up 0.4W of your power. Negligible.
(I made up the figures, so actual ones will be different. Point still stands, 'tho)

A couple of percent diff in drivetrain efficiency is going to make almost no difference to riding speed. You have to recalculate the difference in total drag, and the drivetrain drag is only a small proportion of the total. Imagine you're riding a road bike at about 16mph. That takes about 150Watts. Most of the 150Watts is consumed fighting the air. Some on rolling resistance. A few watts are lost to the drivechain, say its 10W (I'd be surprised if it's this high). 4% of 10W = 0.4W, so a 4% difference in drivetrain efficiency is only going use up 0.4W of your power. Negligible.
(I made up the figures, so actual ones will be different. Point still stands, 'tho)

The 4% loss is applied to the total power at the cranks, not against a derailler system loss. In your example, 4% of 150W would be a loss of 6W. This is actually very good, assuming that the hub really does have this efficiency and that it remains fairly constant over the service life of the hub.

I think there are 2 different ways to approach this-
1. IF I were to exert an additional 5% over my "comfort zone", I would expect my endurance to be MUCH less than 95%.
2. I exert at the SAME level, my speed will be 95%, except I've got a slightly smaller amount of wind resistance, which would result in an actual speed of 95+%.
That's my story.....

I ride a road bike fitted with a Nexus-8 hub. It's great. I can and do keep up with everyone. I did 3 century rides on it this year. Efficiency loss? How much does someone with a derailleur lose when they fail to downshift before coming to a stop? With the hub gear you just click it down a couple of gears while stopped and ride right off when the light changes. In 5th, on the Nexus, you're in 1-1 which is as efficient as it gets. Any I never have any loss due to a poor chain line. Maintenance issues are almost non-existant.

No, it isn't what you'd ride in a time trial, but you wouldn't do well commuting or running errands in a real race car, either.

Everyone worries about/discusses efficiency of hub gears. Nobody ever worries about or discusses the variable efficiency of derailleur set ups - even different gear combination on the same drive train. The typical comment treats all combinations in derailleur drive trains as the perfect base line to which to compare hub gears; the reality does not agree.

A 52/15 and a 38/11 are the same ratio, but the 52/15 is significantly (as these things go) more efficient. The gains are worth far, far more than the negligable grams of weight savings that everyone does focus on. In a review of over two dozen cycling books, not a single one mentioned this.

BTW, modern chains can run significantly out-of-line without meaningful effect on efficiency. The power goes into rotating all those little bushings under load, not flexing the links sideways. See the Kyle/Berto test, above.

HTH,
TCS

Uh, it doesn't work that way. 4% drivetrain efficiency loss does not equate to 4% time gain.

Increases in speed requiring an increase in power somewhere around the square of the increase in speed; x mph divided by the square root of (100% ÷ 96%) should give you something to factor with, unless I'm making a really dumb mistake. (it's been known to happen) If I'm not, then 2.06% longer for the trip with a 4% reduction in efficiency. Or one minute, fourteen seconds per hour.

Do I get an A? :D

The power to increase speed, based on aerodynamic drag only, goes up with the cube of the speed. So to double the speed requires 8X the power. Mechanical resistance is about linear with speed.