# Timing chain derailment



## jeepr84 (Sep 28, 2005)

My wife and I have an Ellsworth Witness out here in Socal. Every once in a while (once every 5 rides) we would drop our timing chain. Usually this would occur on steep, tight switchbacks. My theory was, that as I am negotiating the switchback I probably pause in my pedaling without letting my wife (stoker) know and that causes just enough slack to let the chain ride over a couple teeth. So, please understand I, as the captain, accept full responsibility. I think that frame flex may contribute to it as well...possibly. 

I recently needed to replace my timing chainrings and decided to get a couple RaceFace narrow/wide toothed chainrings and give them a go. They are made primarily for 1X and single speed set ups to prevent chain drop. A simple description is that the tooth width, on the chainring, alternates to fit the natural wide/narrow pattern of the chain.

Well, after about 10 rides I'm very impressed and have yet to drop a timing chain. Another added benefit is that the normal chain "hum" from the timing side is now too quiet to notice.

Am I simply being more diligent and pedaling properly? Or, are these new rings making up for my shortcomings? I'm really not sure, but I thought I would pass this on regardless.


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## PMK (Oct 12, 2004)

Full tooth profile is best. Not a guarantee but less likely to derail.

PK


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## jeepr84 (Sep 28, 2005)

Nothing but respect for your experience and contributions to tandem MTB, but the smallest (narrow) tooth on this chainring is equivalent to standard RaceFace chain ring and the wide ring is much wider. The height of all the teeth are identical. It's just that every other tooth is wider than normal. How is that less than "full tooth" profile? I am absolutely not trying to be argumentative just simply want to understand your statement.


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## Flamingtaco (Mar 12, 2012)

Thinking maybe he's saying that having teeth that match the width of the chain will be less likely to to derail, IOW, the wide/narrow you're using is a fuller profile than using a regular chainring.

Of course, that's not technically the tooth profile, but who cares? You fixed it!


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## PMK (Oct 12, 2004)

Nope, wrong direction guys. I am not talking tooth width, but rather profile if traced onto paper. Some people I have seen use middle chainrings with some teeth lower than others for better shifting. I have not run chainrings with different thickness on the teeth for timing rings. They should work fine and seem to work well for you. 

Sometimes lesser quality rings will have runout and run up / down causing tight spots followed by loose spots.

Others run timing chains too tight and some drooping loose.

Typically though, a decent quality chainring, with full tooth profile and a chain tension just slight loose of tight works real well.

I won't say any one brand of chainrings is better. We have run various brands. Currently we have Salsa stainless but I plan to go back to the thicker aluminum rings for added stiffness when they hit stuff.

As mentioned, excellent it is fixed and working well.

PK


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## Okayfine (Sep 7, 2010)

Any information on other Witness teams dropping the sync chain? I've never experienced that on our ECdM, and did only once on our Burley road tandem, but that was due to an inadequately-tightened BB.

If other Witness teams have had the same, then it may well be a flex issue, especially since everyone's likely running different drivetrain parts. If not, it may just have been a question of the quality of your old sync rings. Did you have a big difference in chain tension during a full revolution?


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## TandemNut (Mar 12, 2004)

Some of the derailment issues are consistent across virtually all tandem brands. I suspect the common factor would be unequal pedaling force between captain and stoker at the same time the frame is being flexed by a maneuver or other factor. We've dropped timing chains on both Ventanas and Fandangos at the same spot on the local trail, and it's a short steep uphill pitch with a turn over a root in the middle of it. I explained to my stoker that the unequal power to the cranks in that situation contributed to it, and that I would back off a bit while she pushed a bit harder. It worked. 
It won't cure every chain derailment problem, certainly, but I think there's something to unequal force on the pedals during maneuvers.
Middleburn says they're making wide/narrow UNOs soon, so that might be an option for tandems with those cranks.


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## jeepr84 (Sep 28, 2005)

TandemNut said:


> Some of the derailment issues are consistent across virtually all tandem brands. I suspect the common factor would be unequal pedaling force between captain and stoker at the same time the frame is being flexed by a maneuver or other factor. We've dropped timing chains on both Ventanas and Fandangos at the same spot on the local trail, and it's a short steep uphill pitch with a turn over a root in the middle of it. I explained to my stoker that the unequal power to the cranks in that situation contributed to it, and that I would back off a bit while she pushed a bit harder. It worked.
> It won't cure every chain derailment problem, certainly, but I think there's something to unequal force on the pedals during maneuvers.
> Middleburn says they're making wide/narrow UNOs soon, so that might be an option for tandems with those cranks.


I think you are spot on with this. Our crux was a steep sharp swithcback out here on one of our local trails. Like I said in my original post, I do think it has to do with unequal pedaling force. With that said, so far the narrow/wide tooth pattern has seemed to prevent any derailments...I'm keeping my fingers crossed. I would have to think if people are having success with these on 1x9 (or 10) set ups with no chain retention devices and standard derailleurs...it has to help, at least a little, on a tandem timing chain. I would be excited to hear of anyone else trying these and whether or not they have similar results.


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## ki5ka (Dec 17, 2006)

quote: nutterAlex "....I explained to my stoker..." Brave lad you are Alex, brave lad... I try NEVER to "explain" NUTT'n to MY stoker! 

Dropped our timing chain again this morning. Just ordered a set of narrow/wide rings. We'll see if that fixes it. 

The big debate was color ;/ but also went from a 38 to a 32T. Haven't really worked out why, but it just seems like it would be better... got an on-going argument in my head over the pros and cons and it's driving me nuts. Going wilderness canoeing for a week, so that ought to settle it.


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## Okayfine (Sep 7, 2010)

32T gives more clearance for obstacles, but more chain wear.

RE: dropping the sync chain - I guess we're just not riding hard enough!


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## DHMASTER (Oct 12, 2010)

I have only dropped a timing chain once. The loss was due to the position of the eccentric bottom bracket. When looking at the eccentric bb from the left side of the bike the bb should be set to proper tension between 11:45 and 9:30 so that any rotation of the bb can only tighten the chain and not loosen it. With proper tension and this orientation it should be quite difficult to loose that chain without breaking it. Perhaps my opinion shouldn't count for much since my t-chain is on the drive side which probably negates any frame flex issues.


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## ki5ka (Dec 17, 2006)

Okayfine said:


> ...I guess we're just not riding hard enough!


lol


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## ki5ka (Dec 17, 2006)

*Narrow Wide*

I like it, we ride faster now 

Something I hadn't anticipated, it is much easier to get the pedals synced now as the chain moves in 2 link increments, making differences more obvious.

Solid as a rock, clearly engages more positively. The smaller size and the heftier construction seems to be much stiffer and stronger as well.


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## Sam Jones (Feb 25, 2005)

Our first mountain tandem was a ~ 1990 Santana Rio. We had frequent problems with dropping the timing chain. After some experimentation and observation I determined that the cause was frame (bottom tube) flex when I would really stomp on the captain's crank to power up a short steep hill, etc. The fix was a combination of running the timing chain as tight as reasonably possible AND moving the chain rings to the INSIDE of the cranks. This reduced the leverage of the chain pull on the bottom bracket axle that is trying to bend/flex the bottom tube.

We later TOTALLY eliminated the problem when we changed cranks by getting the shortest possible bottom bracket axles and having the least possible axle amount sticking out on the timing chain side. The chain was thus MUCH closer to the bottom tube greatly reducing the bending leverage.

Another factor is the size of the timing chain rings. We always run the smallest practical chain rings because it increases clearance of log crossings, etc. However this maximizes the tension on the chain (and thus the bending force on the bottom tube). On or current ECDM we are using cranks that accept a granny gear on the timing side and are using 28T granny sprockets which maximize ground clearance AND minimize bending leverage on the bottom tube. This has been bulletproof.


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## switchbacktrog (May 10, 2013)

I've not checked the price difference between a standard chain ring and a narrow/wide one, but theoretically, having a wider tooth profile should reduce the tooth wear making the NW ring more economical in the longer term.....................or is all the drive loaded onto the narrow tooth?


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## TigWorld (Feb 8, 2010)

Tooth profile at the chain contact edge on a NW ring is same width on the thick teeth as the narrow teeth. eg:


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## switchbacktrog (May 10, 2013)

It looks like some of the drive will go onto the links as well as the roller after a bit of wear (wide tooth).


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## PMK (Oct 12, 2004)

DHMASTER said:


> I have only dropped a timing chain once. The loss was due to the position of the eccentric bottom bracket. When looking at the eccentric bb from the left side of the bike the bb should be set to proper tension between 11:45 and 9:30 so that any rotation of the bb can only tighten the chain and not loosen it. With proper tension and this orientation it should be quite difficult to loose that chain without breaking it. Perhaps my opinion shouldn't count for much since my t-chain is on the drive side which probably negates any frame flex issues.


You have sweet custom bike. I suspect the builder ensured stiffness when selecting the bottom tube. Same side or opposite side drive could be insignificant on your machine.

As for the clock angles you posted, are you using 11:45 to indicate just prior to spindle at highest point and 9:30 to indicate just above centerline for the spindle on the aft side.

I ask based on since you run single side drive, is it possible your clock angle are veiwed from the left side where you probably make your adjustments. For us, I setup our eccentrics to adjust from the right side to avoid the timing ring.

I, whenever possible run the spindle above the eccentric horizontal center line and position it between 1:00 and 3:00.as viewed from the right side.

Confessing though, since the timing stuff on our Co-Motion road tandem has some 9000 miles and required removing a link during a road trip event, I have been too lazy to replace the entire setup even with spares on hand. That bike eccentric is positioned between the 9:00 and 12:00 position as viewed from the right side.

Both setup work fine on their respective bikes and riding. Both bikes run the better design Bushnell type.

PK


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## PMK (Oct 12, 2004)

Sam Jones said:


> We later TOTALLY eliminated the problem when we changed cranks by getting the shortest possible bottom bracket axles and having the least possible axle amount sticking out on the timing chain side. The chain was thus MUCH closer to the bottom tube greatly reducing the bending leverage.


The fantasy design... A frame that has protection for the timing rings by using the concept of running the timing chain down the bikes centerline and allowing the bottom tube to protect it. The cranks would be all 3 of a non drive style, however the BB would require the ability to hub the timing rings. Timing chain tension would be via a two pinch bolt per side setup with individual cups left and right.

A double bottom tube setup would be easier and stiffer.

PK


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## jeepr84 (Sep 28, 2005)

Well, 25 rides into this experiment (15 since my original post) and we have yet to drop a chain. This even included a race where I seriously blew a couple of shifts and we hit numerous switchbacks under full power...our previous Achilles heel. I am definitely a believer. 

I am stoked that others have given this a try and look forward to other long term reports.


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## sportsnapper (Apr 24, 2014)

I read this thread with interest, but didn't really take it all in until now. Today we rode our local singletrack, faster then we've been able to do before. At one point we had a chap follow us as he'd not seen 'anything like that before'. My stoker was putting the power on, and on a section very similar to the one described by Alex


> and it's a short steep uphill pitch with a turn over a root in the middle of it


 we shipped the timing chain.

Looking at it now we're back at base, I think the eccentric could do with a bit more tension, and that's certainly the first thing I'll be doing. But a set of Middleburn narrow wide rings could be tempting.


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## TandemNut (Mar 12, 2004)

Middleburn is now shipping thick/thin chainrings in 4 bolt 104 bcd pattern. We'll have them in stock in the next few days in hardcoat. The UNO T/T's are coming within a month or so.


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## sportsnapper (Apr 24, 2014)

Tightened the Eccentric today - quite a lot of slack there. We're off to the Morvan tomorrow for two weeks, so we'll see what happens there, then perhaps upgrade when we get back. 

Thanks for the info Alex. Matt from Middleburn visits the shop where my son works here in the UK quite often, as there are about 20 miles apart. I'll be asking him to source them I'm afraid...it's a bit more convenient


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## Sam Jones (Feb 25, 2005)

Most of you folks on this board have forgotten more about off-road tandems than I ever knew so I humbly ask: Why would unequal pedaling between captain and stocker have anything to do with timing chain derailment? 

I'd think the timing chain doesn't even "know" how hard the stoker is pedaling but rather only "knows" how hard the captain is pedaling (and thus putting stress on the chain and boob tube)? 

Obviously the captain would have to pedal harder (thus more boob tube flex) the less the stoker was pushing on any given hill/speed so maybe you mean this "indirectly" leads to harder captain pedaling and thus more flex???


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## PMK (Oct 12, 2004)

Sam Jones, please check your pm's for an unrelated question about motorcycles.

PK


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## TandemNut (Mar 12, 2004)

sportsnapper said:


> Thanks for the info Alex. Matt from Middleburn visits the shop where my son works here in the UK quite often, as there are about 20 miles apart. I'll be asking him to source them I'm afraid...it's a bit more convenient


No worries - support your local shop when you can! However, you could help all of us out by asking Matt for the UNO Thick/Thin rings in RS7 style to fit the tandem cranksets. He seems a bit hesitant to make them. We would use them on every tandem crankset we use and sell, but I'm not sure he's convinced of the market potential. 
There will be a Middleburn X-type UNO T/T version available soon, but the offset is too far inboard for most tandems to use them on RS7 crank arms.


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## TandemNut (Mar 12, 2004)

Sam Jones said:


> Most of you folks on this board have forgotten more about off-road tandems than I ever knew so I humbly ask: Why would unequal pedaling between captain and stocker have anything to do with timing chain derailment?
> 
> I'd think the timing chain doesn't even "know" how hard the stoker is pedaling but rather only "knows" how hard the captain is pedaling (and thus putting stress on the chain and boob tube)?
> 
> Obviously the captain would have to pedal harder (thus more boob tube flex) the less the stoker was pushing on any given hill/speed so maybe you mean this "indirectly" leads to harder captain pedaling and thus more flex???


You're way too modest Sam. You've taught me a thing or two about tandems in the past!

As you know by watching other tandems, if one rider is much stronger than the other or is just pedaling harder, the slack in the timing ring on the bottom run (usually, simply because the captain is usually the stronger rider) is increased. This increased slack (which results from inherent flex within the whole bike drivetrain/frame system) enables the chain to derail from less frame deflection, especially when turning or hitting obstacles, which may introduce more twisting forces within the frame structure to the equation.

As you know, a tighter timing chain will derail less often even when the frame flexes; smaller timing rings will derail less often simply because the chainring teeth are closer to the axis of the crank axle, and thus will be a shorter distance out of the plane of the rings when things flex. If both riders put fairly equal force on the cranks, the slack on the bottom and top of the timing chain would be roughly equal, since the stoker's stroke pulls the slack from the bottom run.

Additionally, I don't know how much movement is involved, but I am sure that a disproportionate pedal stroke will also flex the boom tube in a different fashion than if both pedal strokes are equal; IOW, the frame may "twist" more than "bend" in the middle under unequal pedal forces.

YMMV, of course, and I am not any sort of an engineer, but that's what I've deduced from watching tandems off-road, our own experience, and from listening to details from customers who experience the problem.

Or, it may simply be that there is a disturbance in the force at inconvenient times during a ride, and someone's Jedi skills are lacking (most often the captain...again...), thus causing the derailment.


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## sportsnapper (Apr 24, 2014)

TandemNut said:


> No worries - support your local shop when you can! However, you could help all of us out by asking Matt for the UNO Thick/Thin rings in RS7 style to fit the tandem cranksets. He seems a bit hesitant to make them. We would use them on every tandem crankset we use and sell, but I'm not sure he's convinced of the market potential.
> There will be a Middleburn X-type UNO T/T version available soon, but the offset is too far inboard for most tandems to use them on RS7 crank arms.


I'll try my best, I've not met Matt yet, but he supplied new rings for our Longstaff road tandem with purple bolts to match the frame!

We've had a another couple of derailments in the last couple of days, riding trails in Morvan, France. Most demanding stuff we've done, and frankly, at the time it's derailed far too busy concentrating on staying upright rather than analysing what happens below our feet....it does tend to be climbing though.


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## VeganGraham (Apr 28, 2009)

We've had the primary chain drop off a couple of times in the past on our previous tandem.
Our current tandem is single side drive with a Rohloff and we're not getting the problem. I assumed it was because we are using 22t inner rings with full height teeth. This is still a bit of an experiment, it seems to be working OK so far, but I did think that if we get any problems, we'd use bigger 32t SS rings with full height teeth in the middle position.
Those who are dropping chains, what non narrow/wide chain rings are you using?
Are they full height SS rings, or standard triple middle rings with lower tooth profiles?


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## sportsnapper (Apr 24, 2014)

Well, over Christmas I managed to find time to fit the Superstar thick/thin chainrings I bought in November to our Lapierre, and we've ridden the local Swinley trails a couple of times with the new setup. We didn't have any problems with the timing chain dropping off at all. 
When I fitted it, at first I thought it was too tight and stopping the pedals rotating - but after a few rotations the chain seemed to seat well and there's no difference from the original transmission


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## switchbacktrog (May 10, 2013)

They look nice Gareth :thumbsup:. When mine wear out I'll probably use the Superstar ones as well. Have you used the JD Tandems long singlespeed timing chain as well?

Looks like you've fitted some new winter tyres............Hans Dampfs? I've moved the Ardent to the rear and fitted a Minion DHF to the front for the winter.


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## TandemNut (Mar 12, 2004)

For those running Middleburn cranksets, we have a small # of RS87 UNO 32T T/T rings in stock now. We also have Middleburn Hardcoat T/T rings in 4 bolt pattern as well. (T/T is Middleburn's designation for the wide/narrow ring design).


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## sportsnapper (Apr 24, 2014)

Hey John, yes - bit flash - one of the local Swinley boys anodises chainring bolts (amongst other things) so he did some to match. No - I've just left the existing chain on for the moment - appears to work!

Yes, got a recommendation front the son/expert to fit Hans Dampfs - pacestar on the rear and trailstar on the front. Only issue is that the front derailleur catches the tyre a little. I just need to find some time to adjust it - or perhaps bring the chain line out a bit - not sure yet. Also wondering if I should run them tubeless - Morgan thinks so - but not sure how they will go with the weight and pressure exerted on them on the Tandem.

But had our third outing of the year today - and Sally's third ride on Larry since the op. We did Swinley, including some of the red for the first time. Though missed the hard bit of Tank Traps - I saw a big drop off and went left


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## jeepr84 (Sep 28, 2005)

Well, it has been less than a year since I started this thread and I'm pleased to report we have not had a chain derailment in over 50+ rides. It was never a chronic issue, but without running narrow/wide chainrings we would have had, at least, two or three chain drops during this same period with our old standard set up. Simply put, this set up works. I'm also very enthusiastic about others results with narrow/wide chainrings.


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## ki5ka (Dec 17, 2006)

Lots of other drive-train issues, but the timing chain has not dropped since we jumped on this band-wagon 8 months past, and put on wide-narrow. Thanks for the inspiration Jeepr!


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## jeepr84 (Sep 28, 2005)

Nice!



ki5ka said:


> Lots of other drive-train issues, but the timing chain has not dropped since we jumped on this band-wagon 8 months past, and put on wide-narrow. Thanks for the inspiration Jeepr!


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## jeepr84 (Sep 28, 2005)

Well, we have gone almost 3 years without ever dropping our timing chain. The wear rate of the narrow/wide seems no different than standard rings. Based on this, I'm considering my little experiment a success. I hope others have had the same result.


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## ki5ka (Dec 17, 2006)

Same here, and you should see the slop I have in the chain 8O You just inspired me to adjust my eccentric


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