Chain suitability for Rohloff hub gear

[ed.lazda]

A while back, when shopping for a new chain for a Rohloff-equipped bike I was told that a Shimano 6/7/8 speed chain would be suitable as it was "the same size" as a single-speed chain. I've just put this chain on the bike, along with new sprockets, and on the first ride the chain kept coming off, usually when pedalling at high cadence and low torque on downhills. I've never had this happen before with KMC chains. I've had a look at the new sprockets and nothing seems to be bent or off-line.

Is it likely that the chain is the problem here?

Thanks in advance for any responses.

[Jdsk]

"Chain Choice for Rohloff & other questions":
viewtopic.php?t=137199

Jonathan

[mjr]

A 6/7/8 speed chain is not the same as a single-speed chain. I think 6/7/8 is 3/32" wide and single-speed is normally 1/8" wide. Which chain is right for your bike depends on the sprocket fitted. I don't know what Rohloff recommend or what you have. In any case, a 1/8" chain will usually run on 3/32" sprockets (but might be noisy or strike nearby parts), but the reverse isn't true.

More often, a chain coming off a hub gear system is because the chain is slack, either worn or not tensioned correctly, but I've not seen your bike. Have you checked it for wear? Did you think it was tensioned OK until now?

[JohnR]

I've used both the KMC Z1 (narrow) and the KMC X8 (both are 3/32" width) on my Rohloff bike without problems. The likely reasons for the chain coming off are either that it's excessively slack or that sprocket/chainring are excessively worn or, if it's a new chainring, it's made for a wide (1/8") single speed chain and a 3/32" chain isn't properly mesh with it.

There's guidance for the appropriate chain tension on page 12 of the Thorn bike user manual http://www.sjscycles.com/thornpdf/Thorn ... al2Web.pdf.

[Brucey]

do you have a tensioner? Tell us about your chainring and your chainline etc..

[ed.lazda]

Thanks all. The chain is a new one, with no wear, and is less slack than the one it replaced. I've also used KMC chains in the past, with no problems. SJS cycles recommend "KMC e1 EPT 3/32 Inch Chain" for Rohloff. But that wasn't really my question -- what I'd like to know is whether the Shimano 6/7/8 chain, allegedly the same size as the KMC, is likely to be causing the issues I'm experiencing, before ditching a brand new chain.

The setup is a Thorn Mercury with eccentric bottom bracket and no chain tensioner. Chainline seems OK (and hasn't changed). The chainring (45) and sprocket (19) are those supplied by SJSC for use with a Rohloff hub gear.

[slowster]

Are the new sprocket and chainring like for like replacements, i.e. exact same brand, model and number of teeth?

It is often possible to inadvertantly alter the chainline by fitting the ring on the other side of the spider, or by switching the Rohloff spacers (supplied to convert from a triple/double to a single ring) to the other side of the chainring.

I appreciate that you state that chainline seems OK and hasn't changed, but in your shoes I would check the chainline using a long steel rule held against the side of the chainring and the sprocket.

[Brucey]

.... allegedly the same size as the KMC, is likely to be causing the issues I'm experiencing.

all derailleur chain is designed to fall off cogs easily. Some of it is better at doing that. Also not all chainrings and sprockets are created equal either. However, even with an unfortunate combination of parts, it is usually possible to stop the chain unshipping if you use the right setup. BTW the cheapest 'shimano' 9s chain is actually made by KMC. There are also a lot of fake chains out there to be wary of.

[rualexander]

If the chain is properly tensioned with the eccentric bottom bracket then the chain should not be able to jump off.

[cycle tramp]

Most chains are long enough to allow a derailleur system to operate - if you've not shortened your new chain, but fitted it straight from its box, I strongly suspect that the chain is too long. Have you still got your old chain?

[Brucey]

some photos would be helpful.

[PH]

what I'd like to know is whether the Shimano 6/7/8 chain, allegedly the same size as the KMC, is likely to be causing the issues I'm experiencing, before ditching a brand new chain.

The answer is no. Whatever is causing it to come off, it won't be because an 8 speed chain doesn't fit, that's what Rohloff recommend using.

The setup is a Thorn Mercury with eccentric bottom bracket and no chain tensioner. Chainline seems OK (and hasn't changed). The chainring (45) and sprocket (19) are those supplied by SJSC for use with a Rohloff hub gear.

Nice bike, I have the same with a similar ratio (49/19) currently running the posh KMC chain, before that it had an 8 speed.

[ed.lazda]

In light of your responses, I've checked everything over again and set the chain to the upper limit of tension suggested in the Thorn manual, and I'll see how things go for the next couple of rides. Thanks.

[ed.lazda]

Follow-up: seems to have resolved itself. On reflection I think what happened was this: I stripped the factory lube from the chain and gave it a molten wax treatment, and I think it may still have been slightly stiff from the wax when I set the tension. As a result, it loosened up more than expected on that first ride.

It still wasn't as slack as the chain I took off, so I'll probably stick to single speed chain in future.