Rohloff Seal Drag is Good and Wanted!

[Andre Jute]

Seal drag, or even more generically "hub drag", turning the cranks when a Rohloff-equipped bike is pushed is a common complaint on Rohloff fora, often under a presumption that it is an undesirable activity, or even indicative of a threat to an expensive component. Hey, that was my first response too when I was a Rohloff novice, before I thought the matter through.

But is it? I now take a different view. To me it is obviously indicative of high quality German engineering which thoughtfully took the decision to keep out dust by lightweight paper seals. There are also practical uses for this seal drag, to which I shall return.

There are standard setups to measure bearing drag, for instance a dynamometer can compare the friction loss in internal combustion engines which theoretically should put out the same shaft horses or BMEP or whatever measure turns up your wick -- but by the time you get the motor in a car on a track, that considerable amount of work by an expensive white-coat and capital-intensive equipment normally turns out to be wasted because poof! the differences disappear into more urgent feedbacks. And that is starting with big numbers, where a difference could easily be a whole unit or units even if it is a fraction of a percent. Anyway, in automobile racing or commercial consumer car development, you can't afford not to know, so you must do the work even if only to prove to second-guessers that you considered all possibilities.

On a bike, with generally small numbers to start with, not so much. With such small numbers, I like tests that multiply the differences on the whole machine in use. Note, I don't say "magnify" but multiply. Coast-down tests do this well. Of course, that's a loaded test, but to my mind that's the test that really counts, especially with a machine as well-built as the Rohloff hub gearbox. Chalo Colina was right when he quipped that a Rohloff gearbox starts being run-in about the time a Shimano Nexus box lies itself down to die -- I seem to remember that the Nexus Premium 8-speed has an MTBF (mean time between failures, assumed repairable) of 50,000km or say 30K miles. I broke two Nexus boxes a long way before that, between the two of them, but on the other hand in The Netherlands there are Nexus boxes running well enough after a hundred thousand klicks of neglect, so the official MTBF of Nexus boxes (whatever it may be -- I'm giving this from memory) sits on a very wide normal distribution. With nothing but anecdotes to go by, at best we can imagine that the normal distribution of repairs being required on Rohloff hub gearboxes will be skewed towards the high end, lotta miles. Basically, nobody knows the Mean Time Between Failures of a Rohloff box with any statistical credibility ("extremely rare" is not a technical term in statistics!), likely not even Herr Rohloff, who has torn down some particularly high-mileage boxes, and discovered no great wear. It follows that nobody knows the MTTF -- the Mean Time To Failure i.e. the unrepairable end-of-life failure -- of a Rohloff.

Also, counting anecdotes, these dragging seals are either a universal Rohloff "problem" or the owners of the gearboxes with dragging seals are abnormally articulate! So, yeah, if these dragging seals are indicative of some state threatening the lifespan of a Rohloff box, I want to multiply it to where it is a large number so I can make detailed comparisons.

But the truth is, I don't think we're ever going to know. Again, statistically, I bet the majority of Rohloff Speedhub 14s have less than 10,000km/6000m on them, while we clearly have much more than enough anecdotal evidence from a wide variety of riding circumstances that the Rohloff shrugs off such minor use, and is capable of multiples of that distance. Thus, these dragging seals are not a short-term problem, and measuring microwatts on a stand (on an upside down bike with the free oil in a place it normally isn't, as has been suggested, causing a definitely uncommon windage load) will just raise more questions than deliver answers, hence my preference for a loaded coast-down test with the bike in its normal orientation carrying its normal load -- at which point I'm pretty certain the "problem" will disappear, which is why I haven't bothered doing the test.

I confidently expect this question to reoccur again and again and again.

A personal note: I actually welcome the seal drag on the Rohloff as a very useful third hand. I use Magura rim hydraulic brakes on my electrified bike, and these hydraulics are sealed for life, so the brake cutout cannot work by changes in fluid pressure; instead it works by breaking a magnetic contact which operates by 4x magnets stuck onto the brake levers and housings with Pritt's evergummy glue-clay, a real pain to set up if disturbed. The other day, with around 11,000km on the Rohloff, the magnetics went out of whack. The non-drive side of my bike is strongly braced in case I ever want to fit a disc brake (no such chance -- I love the progressive operation of the rim hydraulics), and to fit a kickstand stand capable of holding up the 170kg load rating of the bike. You can see the three rear stays of a cross frame bike, and the punched (drillium!) brace, and other fittings which provide further triangulated bracing, by paging down on this PDF until you reach a page devoted to photographs of the frame end, which I publish so you can see that you shouldn't follow me in abusing any bike which wasn't specifically designed to take bike-abnormal loads at the non-drive rear side; my Kranich can withstand more twisting force between the head tube and the rear frame-ends than a humongous Rolls-Royce motorcar's monocoque; doing what I do could cost you your bike's warranty:
http://coolmainpress.com/AndreJute'sUtopiaKranich.pdf
So to adjust the cutouts, I tilt the bike on its stand until the rear wheel is clear of the tiles, run the motor on the thumb throttle, let the thumb throttle go and, with the electronic "gearbox" in its lowest automatic (pedelec*) setting of 1, the seal drag in the Rohloff keeps the pedals turning via the chain and with them the rear wheel, where a sensor picks up the movement and keeps feeding the motor juice (perpetual motion, anyone?) while I adjust the magnets on the brake levers and housings until separating them cuts out the motor.

Rohloff seal drag to the rescue! I wouldn't give it up for all the tea in China.

*For innocents abroad, "pedelec" is a condition in which motor assistance is proportional to the speed at which you turn the pedals, so the seal-drag speed, pulling the pedals around at a low speed, is just right for adjustments which otherwise would require another person's hands or acrobatics with tie wraps on the brakes and the thumb throttle. In the software with my Bafang/8FUN BB01 installation, there is a lower speed, for parking the bike or climbing stairs, called "P", but it is accessed by pressing and holding a button on the D965 control set button group, so it too would require a third hand. In theory I can also plug in a generic computer controller to keep the wheel turning but that is too much bother as I operate Macs and would have to bring down a PC from the loft three stories up to plug in; the Rohloff seal drag is a handy, quick substitute which doesn't require you to turn off any fail-safe modes.

Copyright © 2022 Andre Jute

EDITED 21 September 2021 to clarify the different implications of Mean Time Between Failures MTBF, which by definition are repairable failures, and Mean Time To Failure MTTF, which is the final unrepairable failure. Thanks to Jeff Liebermann on another forum for pointing out that I should clarify the difference.

[John Saxby]

Rohloff seal drag to the rescue!

Great stuff, Andre.  I haven't (yet) been troubled by my any acquaintance with electric assists or trick Magura brakes, but I have found that making a virtue out of necessity is a good way of dealing with life's vicissitudes. A fortiori, the more sophisticated the better. 

(As the tech-wallahs might say, "It's a feature, not a bug.")

Cheers, mate.

[Andre Jute]

"It's a feature, not a bug."

Thank you for the pointed summary, Master Saxby! You can come again.

[PH]

While not in the least bothered by a bit of seal drag, other than it being a danger to the shins for the pedals to be turning while pushing, it ought to be mentioned that drag can also be caused by bearings not seated perfectly.  Rohloff detail this and the remedy in the manual. It's most likely to occur after the innards have been out of the shell, but I suspect some hubs may be like this from new.  It's also a possibility that wheel building may cause enough distortion to cause it, I have no Rohloff evidence for this, though some experience of it happening on other hubs, it's impossible to correctly adjust cup and cone bearings in an unbuilt hub.
My experience - Of my three hubs the older with the better sealing does it all the time, in all gears, without fail.  The middle one in a smaller wheeled folder with a chain tensioner, does it very occasionally, it may be that the tensioner is providing enough resistance to stop it.  My newest hub benefitted from the remedial action in the Rohloff manual, it went from constant to occasional. 

[Andre Jute]

While we're talking about Mean Time Before Failure (MTBF), which is average time between repairable failures for a particular product, and the Mean Time To Failure (MTTF), which is the average lifespan of the product before a catastrophic failure which cannot be repaired, we should also talk about the Design Lifespan of a product, which is what it says on the tin, a number of years or some other measure (kilometres, miles, tons carried, whatever) told to the designers before they start work, which circumscribes the components they will specify: nobody wants warranty claims that will kill a business, but by the same token sensible managers don't want components that will outlast all the others in the product but are much more expensive than components which will last the predetermined lifespan. It is less than fair to describe this common process as "design for failure", better to see it a "design for an extended warranty".

For instance, the design life of a modern good quality automobile is 20 years, beyond which many insurance companies will now not insure it, but some of its components are known to be good only to 60K/100K miles/kilometers, beyond which use might cause a chain reaction of expensive damage; this number is thus a common warranty period. For example, the timing chain or belt which regulates the camshaft which in turn opens and closes the valves to the cylinders in a non-clashing sequence like formation dancing, is generally replaced at 60K/100K miles/kilometers, and the car then goes another 60K/100K miles/kilometers before it requires replacing again, and a taxi or a car with heavy motorway miles may have it replaced a third and even a fourth or fifth time before the entire car is scrapped at an arbitrary age limit.

And yes, this is also a bicycle example. I can't remember whether it was on this forum on which I wrote that one of the reasons I'm not an enthusiast for the Gates Belt Drive on bicycles with hub gearboxes is that it has a known lifespan in protected circumstances because in a car the belt is usually covered, and thus very likely offers a lesser lifespan in the known unprotected circumstances, in fact sometimes very dirty circumstances, on a bicycle. Also the 60K/100K miles/kilometers I chose above is a common replacement interval for Gates and similar belts -- in cars.

Even if a Hebie Chainglider lasts only as long on a bike as a Gates or other belt drive, it costs only fifty Euro to replace, including postage, and is a quick job by the owner, requiring no special tools. The Gates Drive requires special tools, costs several multiples as much as the Chainglider (plus any number of chains), and is very likely a bigger replacement job than most cyclists want to undertake, especially considering that they bought the Belt Drive to avoid chain maintenance and adjustments.

I think in the long run the Chainglider will prove a better bet for those of us who already have and understand it, though I also think the Belt will eventually come out on top because it is technologically more advanced, and as a mass-produced item has lots of scope for cost reduction, which the Chainglider does not share to the same extent. In addition, some of us have experience of Hebie being a -- shall we say -- a less than quickly adapting firm...

By the way, we've just discussed, without mentioning it specifically, the reason most bicycles with Rohloffs are built on steel or aluminium frames rather than carbon fibre: bicycle makers instinctively know the Rohloff is likely to outlive carbon fibre and therefore choose aluminium with its long lifespan or quality steel with its extra-long lifespan for the frame.

[PH]

By the way, we've just discussed, without mentioning it specifically, the reason most bicycles with Rohloffs are built on steel or aluminium frames rather than carbon fibre: bicycle makers instinctively know the Rohloff is likely to outlive carbon fibre and therefore choose aluminium with its long lifespan or quality steel with its extra-long lifespan for the frame.

Was this written in jest?  I can't see the joke in it but can't take it seriously either.
The types of bikes you're likely to find a Rohloff on will be made of metal regardless of the gearing system. I say likely because there may be examples of carbon touring/trekking bikes, but they will very much be the exception.
There are some carbon framed MTB's and the new type gravel/adventure bikes, but not usually in the same style as those bikes we see with Rohloffs.  Another factor is that carbon manufacture doesn't lend itself to short run production.  Aluminium on the other hand seems to be coming back into fashion, at least on road bikes. 

[Andre Jute]

Was this written in jest?  I can't see the joke in it but can't take it seriously either.

Absolutely not. I wouldn't tell you a joke, at the risk of wasting more time explaining it.

[PH]

Was this written in jest?  I can't see the joke in it but can't take it seriously either.

Absolutely not. I wouldn't tell you a joke, at the risk of wasting more time explaining it.

Thanks for clarifying, I do hate it when I don't get a joke.
That being the case, point two stands -  There is no correlation between Rohloff hubs and frame material. That's easily established, find a Rohloff bike, look at a derailleur equivalent and compare frame material.

[Andre Jute]

Was this written in jest?  I can't see the joke in it but can't take it seriously either.

Absolutely not. I wouldn't tell you a joke, at the risk of wasting more time explaining it.

Thanks for clarifying, I do hate it when I don't get a joke.
That being the case, point two stands -  There is no correlation between Rohloff hubs and frame material. That's easily established, find a Rohloff bike, look at a derailleur equivalent and compare frame material.

Eh? I rather assumed a sentence like "Another factor is that carbon manufacture doesn't lend itself to short run production," would be a joke, or at worst sarcasm. Surely you must know that fibre reinforced plastics are the most malleable materials for the shortest run of production imaginable, the one-off special or prototype. If it isn't a joke, you should explain what you mean.

Of course most bikes with Rohloff hub gearboxes are made of metal. I said so. I don't know why you thought it was worth an argument.

But they aren't touring bikes or road bikes. You just have an extreme case of bias confirmation: you have touring bikes and Rohloff gearboxes, so you see touring bikes with Rohloff gearboxes. The Rohloff was designed to be a mud-plugger's box, and if you go to Germany, where most are sold, you'll find them on plenty of offroad bikes, which are almost without exception metal-framed. Or read the net Rohloff fora, and note their active membership and the bikes they're for.

So, yes, there is a correlation between Rohloffs and frame material, for historical reasons. Perhaps you meant to say there isn't necessarily a correlation between Rohloff and frame material, which might perhaps be arguable from a theoretical viewpoint, though I wouldn't take on such an obviously uphill task.

I'm afraid that must be my last contribution to this branch of the thread.

[PH]

Eh? I rather assumed a sentence like "Another factor is that carbon manufacture doesn't lend itself to short run production," would be a joke, or at worst sarcasm. Surely you must know that fibre reinforced plastics are the most malleable materials for the shortest run of production imaginable, the one-off special or prototype. If it isn't a joke, you should explain what you mean.

The quick answer is somewhere around $60,000 to $100,000 for a frame mold to do a full size run of one frame model.
https://bikerumor.com/aasq8-how-much-does-it-cost-to-mold-a-carbon-bike-head-tube-woes-and-fat-bike-29ers/

What you said:

the reason most bicycles with Rohloffs are built on steel or aluminium frames rather than carbon fibre: bicycle makers instinctively know the Rohloff is likely to outlive carbon fibre and therefore choose aluminium with its long lifespan or quality steel with its extra-long lifespan for the frame.

You made a link between Rohloffs and frame materials, frame builders choose the material because of the lifespan on the hub - It's what you wrote!
There is a link between bike type and frame material, obviously.  But it has nothing to do with the statement you made above.