Wha' happens when the chain falls off?!?

[pdamm]

Dan

Here is what I was thinking:

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

I suspect you may have an issue with that approach.  Unlike derailleur bikes the rear sprocket does not always rotate with the hub casing.  The sprocket will go faster or slower than the hub depending on which gear you are in.  The silicon band will be pushed onto the rear sprocket by the shape of the hub.  As a result there will be additional friction between the sprocket and the band.  You could just put a couple of layers of duct tape of a suitable color on that part of the hub when it is clean and new.

Peter

[Danneaux]

I suspect you may have an issue with that approach.

::stares::

You know...I never thought of that, but I am surely glad you did, Peter! And then were thoughtful enough to tell me!

Thank you! Yes, my derailleur roots are showing, and you are absolutely correct. A little black duct tape would do the job much better and would rotate with the hub, avoiding any possible conflict with the cog.

Whew! Boy, I'm glad you saved me on this one, Peter. An outstanding example of the collective brainpower of the Forum.

All the best,

Dan. (A real face-palm moment there, whew!)

[expr]

Dan,

Is there any way you adopt the same approach as your suggestion to the front chainring. For example, using the lower rear pannier mounting hole to fix on a small flat bar, say 10mm wide x 2mm thick and affix a small rubber boot on the end or hard plastic end cap that acts as a fixed guide.... So in the case of the chain trying to de-rail it will be guided by the bar to go no further outward than the rubber/plastic boot... Kinda like a fixed derailleur..

The boot distance will be set by bending the bar, and will only come into contact with the chain in the event of a possible derailment, if used in conjunction with one fitted to the front as per you o/p then the only way it can come off is outbound on the front, however if you used something similar to a fixed from derailleur both sides would be covered...  Any thoughts.... Dave

[Danneaux]

Is there any way...

Hi Dave; I'm delighted you've joined the discussion! Always good to have you on-board.

I think what you've outlined is the way forward, and my mind has been working along similar lines at this end. I was out in the shop last night, using my miniature bending brake to put some nice, tight corners on some sheet stainless I cut to fit with the electric bandsaw and die-grinder. It looks promising.

What I was thinking was something that would resemble (with regard to position, of course) the Rohloff chain guide (Vik Banerjee, late of this Forum, has a nice photo of one here: http://www.flickr.com/photos/9932605@N08/2472121373 ) and attach it to the right dropout. Folded out of sheet stainless, it wouldn't be very thick.

The right dropout on the Nomad has two threaded bosses, and Thorn have a stainless adapter that bolts to them to provide a single 6mm boss for mounting the rear rack. It might be possible to use longer adapter bolts to capture the chain guide on the inside using a couple nylock nuts.

I like your approach as well, and perhaps something in the middle will do the trick. You've got me thinking a small block of polycarbonate could be milled to do the job in that same location. If I did this, I'd take care to chamfer the entry and exit to avoid snagging the chain if it came off, something like this:  )   (

I'm really a "bug" for keeping my derailleur drivetrains clean and well-adjusted, so it is unlikely I will ever let the Rohloff chain stretch enough to come off. On the other hand, a person can't always foresee all problems midway on a long tour, and it would only take once. I'd really hate to have the chain tear up the beautiful black-anodized finish, so a little "chain watcher" would surely do the trick.'

Thanks, Dave; brilliant idea as usual!

All the best,

Dan.

[expr]

Dan, yep that looks like what I what I had perceived.... Great looks good too.

Polycarbonate... Hmm should be ok, however I reckon that polypropylene or nylon 66 would be "more forgiving".

The only down side to the idea with the guide at the rear only taking care of the bottom side of the sprocket is that in the event of peddling backwards while negotiating some rough terrain is that derailment could happen in reverse, therefore requiring chain guide, or guides to be effectively mounted top and bottom of front and rear sprocket / chain wheel...

Hmm sounds over the top I know, but I do think that the front one you have shown would suffice for the front and an adapted one for the rear would cover most eventualities I would think..

The only thing I would add is that my original thought for just a single sided guide would be better if a u shaped guide that straddled the chain but didn't touch it (similar to front) were used to prevent chain derailment either side of the bottom sprocket IE: rohloff side & frame side.

I also just had a a blonde moment thinking that the chain and rear sprocket could be magnetised, but then realising how stupid that would be, however I decided to post anyway just for that "feeling silly" moment.

[Danneaux]

I decided to post anyway just for that "feeling silly" moment.

Oh, I've had plenty of those, Dave! Look up just four posts higher in this thread for my last one. Thank goodness for Peter catching me on that one!

I think we're honing in on the ultimate solution to this one. I agree: Polycarbonate is likely out; Polyprolylene sounds better...a little softer, anyway. I'm going to ponder some more, and probably go back to metal. I like your single-sided guide idea. Whatever is used, it has to be well-anchored else the carnage that resulted would be worse than what I'm trying to prevent. The chain has mass and velocity, and there's a lot of possibilities for damage if it caught the edge of the chain guide. Yikes.

A fun project to ponder this afternoon! Thanks, Dave!

All the best,

Dan.

[il padrone]

Wouldn't it be just as good to................... tighten up your EBB

 

[Danneaux]

Wouldn't it be just as good...

Yes! Even better! Best yet! 

Dan.

[NZPeterG]

Wouldn't it be just as good to................... tighten up your EBB

 

I was just thinking the some!
Just adjust your drive chain! After running a Rohloff for over seven years the chain will not come off if adjusted right.
The chain wear on a rohloff bike is very low, I raced 24 hour MTB races for years and 300km plus in three days with loads of mud!
If you oil your chain and keep it adjusted all is good.

Pete......

[NZPeterG]

If you have too be over the top! you can fit a DH chain guide from Rohloff
http://www.rohloff.de/en/products/speedhub/dh_chain_guide/index.html

If you do not like a Rohloff Chain guide CC
http://www.rohloff.de/en/products/speedhub/chain_guide_cc/index.html

You can go with a Paul Chain Keeper
http://paulcomp.com/ckclamp.html

All over the top unless you ride a Downhill MTB

Pete.....