Wha' happens when the chain falls off?!?

[Danneaux]

Hi All!

In trolling through the Forum archives (and Thorn's user guide and the Rohloff manual), I see Rohloff drivetrain chains are meant to run with considerable slack. This is understandable.

I also see some folks have not tightened their eccentrics to take up unneeded slack until one day, the chain falls off.

Uh...what happens when it "falls off"? Does the fallen chain cause damage to paint? I have also read some Rohloffs (at least early in their lives) may have some slight drag when freewheeling. Would this be enough to propel the fallen chain across the face of the bottom bracket, damaging the paint?

If so, have any of you taken precautions against the day when this might happen? I use n-Gear JumpStops ( http://n-gear.com/index.html )to prevent inner chain derailments on all my derailleur bikes, and I suppose one could be adapted to single-chainring Rohloff use. Similarly, a person could fit an inner chain guard/bashguard, or simply place a piece of protective tape on the bottom bracket (eccentric housing) against the fateful day.

Should I be worried? Any battle-scarred Veterans d' Rohloff care to share?

Many thanks in advance!

Best,

Dan. (the more I learn, the less I know!)

[Big_Jim]

Dan
I run my Rohloff on a hardtail mountain bike where it lives in a perminent state of muck, grime, grit etc in the Peak District. From experience, if you don't keep an eye on how much slack is created by wear and tear of the above, the chain does eventually fall off (especially going downhill over rough ground). When it does, it can create a gouge around the alloy shell if you don't spot it when you first try to pedal. I assume this is similar to that which other contributors were worried about with the chaincase issue.
Mine has done this several times over the last few years and apart from looking unsightly I don't think it will have done any long term damage - time will tell. As for putting it back on, I feel it is slightly easier to put the chain on the rear sprocket first and then put it on the bottom of the chainring and back pedal slowly to get it all back on. You just end up with oily fngers - at least I always do.
Jim

[Danneaux]

Hi BigJim!

Thanks for the feedback; great hearing from you.

I'm an experienced cyclist, but all my exposure has been with non-Rohloff bikes, so I am on a steep learning curve as a Rohloff newbie awaiting my Nomad.  I'm trying to address any issues before they become uh, "issues", so your experience really helps.

I'm thinking I may rig up a spare n-Gear JumpStop to catch a worn chain from someday falling off the inside. I'll be running a Thorn pie-plate/bashguard style chainring protector on the outside, so that part is already addressed; just wanted to prevent any possibility of future gouging on the inside. It may be my concerns are a bit overblown because I still remember riding with a friend whose derailleur chain dumped to the inside just as he started a steep hill climb. It took out not only the front derailleur, but the brazed-on cable guide atop the right side of the bottom bracket -- quite a feat, and a sad one, too. I brazed on a replacement for him, but it took a bit of brass to fill the divots.

I maintain my equipment carefully, so should see an overstretched chain early enough to take up any unnecessary slack, but I suppose it can't hurt to be a bit proactive early on until I get a feel for how quickly the chain can stretch.

All the best,

Dan.

[JimK]

I am neglectful not only in letting my chain get too slack so it falls off, but in not even thinking about the potential paint damage that this can easily cause! I haven't noticed any chipping, but I could easily just be looking in the wrong places!

Thanks for the wake-up call!

[Danneaux]

Hi JimK!

In looking at my tandem, which also uses an eccentric to tension the timing chain, I think most worries about dropping a Rohloff chain could be addressed with a short length of electrical or other tape wrapped around the top and forward side of the bottom bracket.

After all, as soon as the chain is free, one stops pedaling! That pretty much limits the most likely damage in road use to a paint-scuffing, and the chain's links are rounded and greasy/oily, which would further reduce friction. Looking at it that way, the short length of tape should do the job pretty nicely. I think I might apply a short length of my favorite Trim-Brite "Blackout tape", intended to renew worn automobile windshield trim. It is a perfect match in tone and color for Thorn's matte black, comes in a long (1-3/8" x 20') roll, and has a low-creep adhesive so it doesn't shrink and leave a sticky margin. Best of all, I have found it can be carefully peeled off and renewed when necessary without harming the powdercoat beneath. Available in American auto parts stores and from a number of online retailers, including these:
http://www.summitracing.com/parts/SLC-T9005/
http://www.amazon.com/dp/B00029XD62/?tag=newaug2012-20

Carefully considering the above, I think it unlikely you suffered even a paint-scuffing, Jim, and probably no chipping at all. Whew!

All the best,

Dan. (Prepared! For what, we're not sure...)

[wheezy]

Another MTB here. I can't recall ever losing the chain while out riding, and I also let it run fairly slack.

I may not ride any big drops, but the bike has gone on without me a few times, bouncing through the trees and cart-wheeling down the slopes.

[swc7916]

Rohloff drivetrain chains are meant to run with considerable slack...

I don't see reason why they should have any more slack than a single-speed or fixed-gear bicycle.  It's no different than the timing chain on a tandem; if it ever comes off it's because you neglected to adjust the eccentric as the chain stretched.

[pdamm]

Dan

I had an experience with this a few year ago soon after I bought my Raven Tour.  I had deliberately let the chain go slack to see what would happen.  And I found out.  On this particular day the ride had two unsealed sections, one at the start and one at the end of the ride.  Each section was about 20km and there was about 40km of sealed road in between.  The unsealed section at the start was the roughest but both can be described as rough.  This was not single track but on public roads.  I had no problems on the first section but in the afternoon on the second unsealed section the chain just would not stay on!  It was as though while riding on the sealed section the chain had worm past some unseen limit and literally every km or so the chain would come off.  I was in a rush to get to a post office in the next town before it closed otherwise I would have stopped and removed a link (as it was way past due).  As a result I was stopping every km to put the chain back on.  I was trying to be careful to keep the tension even on the pedals throughout the full cycle but that did not help.  The chain kept on popping off until the last few km before the end of the ride where the sealed road started again and it behaved itself.

In every instance the chain came off the rear sprocket not the front ring.  I now have some scratch marks on the hub casing as a result.  But they are minor.  It took a bit of fiddling to work out how to get the chain on the rear sprocket quickly with panniers in the way but I did work it out.  Incidentally there have been a couple of other occasions when the chain has come off and in every case it came off the rear sprocket.

Since then I have been careful to make sure my chain tension is within the recommended 40 – 60 mm of slack when I know I am going on unsealed roads.

I suspect the tension on the chain as it is drawn on to the front chain ring while you are pedalling is what keeps it on the front chain ring.  Conversely the slack on the underside allows the chain to flap about as it is drawn on to the rear sprocket.  If there is too much slack in the chain and if it flops about in just the wrong way it can hop off the teeth as it is drawn onto the rear sprocket causing the chain to come off.

If you keep an eye on your chain tension I would expect the chain will stay where it is intended and you won’t have any problems.  That has been my experience ever since.

Peter

[Danneaux]

My! What a description, Peter! You are a keen observer of just what is going on, and like the other correspondents, it appears a dropped chain is indeed going to fall off the rear just as you describe and for the very reasons you've cited.  Well done, and my compliments on your close observation and cross-correlational analysis. I would suspect any scarring to be more visible on a black-anodized hub, but it can't be good on any.

To be honest, I had not anticipated any problem with derailing at the rear, and was concentrating my efforts at the front. Hmm. This is cause for a re-think of my present strategies.  If it dumps on the wheel side and scars the hub, that is at least "better" (less-worse?) than having the chain somehow ride up and jam against the inside of the dropout. <shudder>

I...am getting an idea.... More specifics later if I can bring it to fruition.

I don't see reason why they should have any more slack than a single-speed or fixed-gear bicycle.

Hi swc,

<nods> Yes, I see what you are saying; I should have been more specific. I was thinking "slack" compared to a derailleur drivetrain in which the chain is always under dynamic spring tension by the jockey and tension pulleys in the derailleur cage. I am careful to keep an eye on my tandem's timing chain and have never dumped it.

...the bike has gone on without me a few times, bouncing through the trees and cart-wheeling down the slopes.

Lee...your bike is simply not getting out enough on its own, and is taking every opportunity to run, to gambol, to be free as a bird, turning cartwheels of joy....

I run my Rohloff on a hardtail mountain bike...

BigJim...by any chance, does your hardtail MTB use a chain tensioner? If so, do you think that might make any sort of difference, positive or negative, in retaining a stretched chain?

Thanks, everyone, for your thoughts; please keep them coming.

All the best,

Dan.

[martinf]

If you keep an eye on your chain tension I would expect the chain will stay where it is intended and you won’t have any problems.

I've been running hub gears (mainly Sturmey 5-speeds) on some bikes since the late 1970's, something over 100,000 kms. On bikes properly set up for hub gears (i.e. possible to adjust the chain length without a pulley type tensioner) I have only ever had the chain come off once.

So I don't think it should be much of a problem with a Thorn Nomad if you adjust the eccentric to take up chain slack. In my case, probably even less likely, as I am almost certainly going to fit a Chainglider. I can't really see how the chain could fall off inside one of those.

Chains have come off much more frequently on other bikes with derailleurs or hub gears with pulley-type tensioners.

I've dropped the chain once on my old MTB with vertical dropouts and Nexus 8 conversion, so I increased the tension slightly in the Singleator tensioner. Incidentally, the chain came off the front, I had just started to pedal after coasting downhill.

I think using a proper single-speed chainwheel with higher tooth profile should help keep the chain on the front - on my Nexus 8 conversion I just kept the largest chainring (44T) I used in the derailleur configuration.

[Danneaux]

Please,

Does anyone know the outside diameter of a Rohloff hub just inside (wheel-side) of the cog? This would be the part that looks slightly concave and eventually rounds up to the right-side spoke flange.

Thanks!

Best,

Dan.

[Big_Jim]

Dan

BigJim...by any chance, does your hardtail MTB use a chain tensioner?

Nope, I had a mid life crisis and had a Dave Yates custom MTB frame with eccentric BB made to measure. Being six foot four and eighteen stone (250 pounds) there aren't many frames out there "off the peg" In many ways its similar to a Thorn Catalyst, just with Reynolds 853 tandem gauge tubing to cope with my weight.

Jim

[JimK]

Does anyone know the outside diameter of a Rohloff hub just inside (wheel-side) of the cog? This would be the part that looks slightly concave and eventually rounds up to the right-side spoke flange.

I measured 2 inches, or 5.2 mm. Ought to be accurate +/- 1 mm I think. I made myself a crude outside caliper with a couple pieces of corrugate cardboard! This should have picked up the diameter just on the wheel side of the chain. I didn't take off the chain or sprocket to see if there is any funny step-down right at the very outer limit of the hub!

[Danneaux]

Jim!

What an outstanding job of measuring; thanks so very much!

Here is what I was thinking:

Stretch one of those silicone rubber "charity bracelets around the hubm just inside (wheel-side) of the sprocket.

Looking through eBay's listings this morning, I found these:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300736453504&ssPageName=ADME:L:OC:US:3160

12mm wide x 18cm; they're supposed to stretch and are billed as "tough". They have no logos, and I got black. Cost is reasonable at USD$1.29 postpaid from Hong Kong. I don't know the seller, but they're at 100% positive feedback for 124 transactions and it isn't much money to risk. 12 available colors, too.

My reasoning is -- assuming it works at all -- that 12mm would pretty well catch any chain that derailed to the inside, off the cog. The silicone bracelet would serve as a barrier to scratching, and being black-on-black, shouldn't show up too much. One of those things I will probably fit and never think about again until or unless the chain stretched enough to derail on me, in which case I can suddenly remember, puff out my chest, and say "Oh, how provident!"  Yeah, right. 

Thank you again, Jim, for your measurements; you're a star for sure!

All the best,

Dan.

[JimK]

(I let my photo editor tweak the colors... my hub is dirty enough but more just grey goo than brown goo!)

The hub is still rather conical right by the sprocket. Hmmm, the circumference of the wrist band is 18 cm, the hub circumference is like 16.4. Going to be loose in there. Could the wristband get caught between the chain and the sprocket? Maybe not loose enough for that. Interesting puzzle!

My hub isn't anodized anyway. All a chain drop will do is cut a groove in the goo!

I forget whether I have had the chain fall off just once or maybe twice. Seems to have come off in the front for me. No idea why! I was coming down a big hill... I think I was coasting and then started pedaling. Some decent bumps along the way there, a bit of rough pavement. Just the luck of the chain bouncing around, I would think. If you keep pedaling the slack should be at the bottom and so the chain will come off in the back. If you are lazy and coast then the friction in the hub will push the slack over the top and the chain will come off in the front. How's that for a theory!