preventec47

I have a timing chain that I assume is stretched and came off causing injury to my stoker and associated negative attitudes.

I dont see a way to attach an idler gear to maintain tension so my only option is to get new chain that I hope will be shorter and less likely to come off.

Since the timing chain does not shift I was wondering if a much heavier duty chain is available that would resist stretching longer.

I can take a micrometer and measure the width of the teeth on the timing sprockets if that would help. As it is, my tandem has an 8 speed
Cassette and is probably 16 or 17 years old. I guess I should replace the shifting chains as well. I googled bicycle chains that stretched
the least and the consensus is that the stainless steel chains last much longer but I cannot find them for older 8 speed systems. Believe me money
is no object compared to a big bloody gash in my stokers calf.

conspiratemus1

Do you not have an eccentric in the front bottom-bracket shell to take up slack as the chain wears?

preventec47

Ah I forgot about the eccentric adjustment. I bought the bike used with a lot of miles on it and it would make sense that the chain has stretched. Now I am also wondering if the sprocket teeth are also worn. The chain replacement is a gimme but the sprockets are much more involved.. I am going to do some googling to see if I can find out how to check for sprocket tooth wear.

Meantime, back to my original statement, I would like to buy the most durable chain I can find. I see that the teeth are much thinner than the main sprocket body. I have a micrometer, are there any go, no-go widths of the teeth or is the wear more prominent in the curveature shape of the tooth ?

bwebel

You could go for a track chain/chainrings that would be wider/theoretically stronger. But I think you are really chasing something that doesn't matter much. You got a used bike that was somewhat out of adjustment/worn and you didn't correct for this. If you just keep the eccentric adjusted properly, you are very unlikely to have further problems.

The real question is how to make your stoker feel comfortable again. I'd probably replace the chainrings regardless of their wear just to make the stoker feel better that you replaced everything with new parts. Or you might look into a belt drive for the timing chain, this could address your stoker's worry.

reburns

Not trying to talk you out of new chainrings or moving to a belt, but be aware that timing rings only wear on one side of the teeth, meaning the leading face of the captain’s teeth and the trailing face of the stoker’s. What that means is that swapping the rings gives you a new set of wear surfaces.

Timing chains last a lot longer than drive chains since they don’t have to shift and flex sideways. A lot of people use the same type of chain for timing as they need for the drive chain so that repair parts are interchangeable.

#1 is to make sure the eccentric is adjusted properly.

diabloridr

To add to what others have said, since the timing chain does not not shift, there is no need to specify a chain compatible with number of speeds in the current cassette.

6 or 8 speed compatible chains can be specified, will be cheaper and may be marginally stronger as well.

conspiratemus1

The reason I asked about the eccentric was that if you adjust and maintain your bicycle properly you will not need to waste time searching for magical mythical stretch-proof Superchains that won’t fall off despite zero maintenance. All chains and rings wear. Eventually your timing chain will become slack. And then it will fall off. The problem is not the chain. It’s you.

if your tandem is 17 years old and has never had either chain replaced, likely the timing rings and the rear sprockets will be too worn for new chains to mate properly. The new chains will lift and skip on the old sprockets/rings — that’s how they tell you they are worn out. On the front, that means the chain will fall off. Again.

preventec47

This is what I wound up getting for my timing chain. I figured the EBIKE chain might be a little stronger than normal chain and the coating
should help resist corrosion and perhaps extend the life of the chain ......
product link https://www.kmcchain.com/en/product/...t-8-speed-copy

preventec47

Yes you are correct. At this point, I have lost the stoker. Maybe gentle coaxing and proof of new components will help lure her back in the future. I must confess to a much
bigger mistake I made which contribueed to this. At the stokers request I removed the toe straps on her pedals and that caused her to lose the pedals many times during a high
cadence stretch and I believe that might have been the precursor to whatever happened that caused the chain to come off and the gear tooth to gouge her leg.
To further exacerbate the problem I as captain was unaware of the pedals spinning wildly as she would not inform me and try to catch the pedals while they were spinning.
Communication is key and the danger of spinning pedals I now know is equal to or greater than the risk of going down without being able to pull your feet out of the pedals.

JanMM

We've only dumped a timing chain once on our recumbent RANS tandem. (Never on the upright KHS we previously rode.) The RANS has an aftermarket idler which directs the chain and is also easily adjustable for tension - much easier than the original stock idler system. In spite of the ease of adjustment, I had neglected to keep up with checking tension - resulting in the chain's jumping off on a bumpy stretch of pavement on a ride a few years ago. Thankfully, we got stopped with no problems and was able to get the chain back on with proper tension with a hex wrench. As you have found, a loose timing chain can result in much trouble.
Yes, communication is paramount for riding a tandem but surprised you didn't notice a problem before things went from bad to worse for your stoker.
My stoker has always ridden with either half-clips or, now, with clipless pedals. She has never used clipless on a single bike but no problems on our tandem.

IPassGas

Ask yourself, why ride a tandem? There is the fast, drafting stuff which we could care less about. It is because of the shared experience of riding together. Riding with fun and enjoying the sights is initially strongly connected to an understanding of abilities. That takes times to figure out and requires talking about stuff and adapting. Talking and listening about stuff during the ride and after. Cadence is one element, which can be aided with different crank lengths. Good luck, I hope you can slowly earn your stoker's confidence again.

LV2TNDM

This isn't a bad idea. However, "stronger" may not mean longer life. But given the higher torques ebikes put out, common sense would say an ebike chain SHOULD last longer. Tensile strength would be the "brute strength" metric that would describe "strong." However, it isn't really important on a timing chain because only one rider is applying force to it. If you were to improve tensile strength anywhere, it would be the main chain since it's having to withstand the force of two riders. But this isn't what breaks most chains anyway - it's usually applying full force while shifting, which pops a side plate off and the chain separates.

I think you're trying to improve durability to reduce "stretch" or elongation. There are myriad parameters that go into making a chain. Quality steel, heat treating and plating are probably the three most important. Get the right combination, and you can have a very durable chain. However, which brand is best??? That's the million dollar question to which there is really no objective answer.

It would be nice to have an independent chain testing organization that could put chains through proper testing to determine durability. There are people out there testing chains and lubes, but they all seem to have an axe to grind - either promoting their brand of chain or chain lube. Hard to find true objectivity.

But the problem there is that product models are constantly changing as are those producing the chains. So while one brand and model could be the test winner, two months later the model could go out of production, or the manufacturer switch producers, change specs, pick lower cost materials, or other cost-saving measures you'll never know about. In other words, it's hard to find "the best" that persists as the best.

All that said, I know Co-Motion uses 6,7,8 speed chains for their tandems under the assumption that a wider chain has more beef and metal, and should therefore last longer. But again, it depends on the materials and production processes.

I just picked the KMC all-silver chain as my go-to replacement. It seems to get good reviews, so I bought a bunch. I just replaced the 30-year old Sedisport Silver chain on my road tandem. The timing chain actually has virtually no measurable wear, but the main chain is just about 1/16". Either way, time to replace. Turns out the KMC shifts much better. Better on my road bike as well.

I still cannot believe I got that much time out of my original road tandem chain. I haven't put that many miles on that bike, but certainly not zero! The Sedis Silver was THE durability winner in my book. I wish I bought a case of 'em back in the day! Oh well, we'll see how the KMC's last.

And the timing chain ring swap suggestion is excellent. It's a great way to double the life of one tandem component.

Good luck.

Leisesturm

So, I'm confused. Did the timing chain derail, or did the Stoker lose the pedals because of a lack of pedal retention? It matters. There seems to be a tendency to overreaction on the parts of both Captain and Stoker in the o.p. Buying e-bike chain seems excessive since there isn't any indication that a new 'normal' chain wouldn't be adequate. The part about a "high cadence stretch" has me wondering about the Captain's ... sensitivity, if you want the truth. The Stoker may not be overreacting. Captain, we need to talk. At this point I'm pretty sure your problems are not of components and their quality or tolerances. We need to know more about how y'all's came to own a tandem, how and where you want to ride it and ... other stuff like that ... or not. But I think it could help. FWIW.

Trakhak

Once you get the mechanical problems sorted out:

Tell the stoker to give you a kidney punch any time you start pedaling too fast or for any other violation of tandem buddy courtesy.

Persuade the stoker to try foot retention again.

For the first few rides once your stoker is again willing to ride with you, go for much shorter rides far from traffic and hills.

Your stoker will probably eventually ask to resume the longer rides.

All this assumes that you haven't permanently burned that bridge.

preventec47

Sorry to confuse you. I have been riding tandems for 20 years but I recently acquired another straight bar very nice tandem with fat 26 inch tires and about 17 or 18 yrs old.
I have ridden it about twenty times and put a hundred miles on it solo through quiet neighborhoods with very steep hills. The recently acquired bike uniquely has very low gears
enabling the climbing of steep hills compared to my drop bar locomotive road tandem. This was a first time tandem ride for a new stoker and I had the conversation
about 123 go, me letting her know when I was shifting, and letting her know when to coast and stop peddleing . We did a careful orientation ride on flat roads to get the hang of everything, During the initial introduction to the tandem the new stoker was nervous about her feet getting caught in the toe clips and asked me to remove them so I did.
I have never before ridden a tandem with rear pedals that did not have toe clips so I was unaware of the potential for the feet to come off and the whirling pedals ability
to cause injury. Regarding the injurious accident, we were approaching a super steep mother of a hill and I prematurely shifted several gears too far and wound up being
in way too low of a gear and this resulted in zero pedal resistance and a very rapid cadence where I am pretty sure the stokers feet came off the pedal and shortly
thereafter the chain came off which was immediately apparent because of no acceleration up the hill. We of course stopped and there was a lot of blood.
The stoker didnt really want to talk about what happened but she said she was sorry and it was all her fault. Thats all I know. That is when she informed me
that during our introduction ride that her feet had come off the pedals more than once but I never knew about it. My analysis of the event is flawed because I do not
know exactly how the stoker got her feet to a position where the sprocket would gouge her leg and cause a derailment or whether the derailment happened
first and caused the injury. I will never know. It did seem the chain had stretched a bit or at least it had more slack than I would like so I set out to get
a new chain. After some research, it appears the sprocket teeth are showing no signs of wear. I do not know the age history of the chain as I recently acquired the
bike as used and rode it quite a bit without any problems. I am putting the toe clips back on and will never remove them again. My situation is that of a situation
where I am likely to have multiple first time tandem riders and the cleated shoes/special pedals is just too much of a logistics nightmare for just an introductery ride.
I will make my equipment as bullet proof as possible and I will now also engage in a more comprehensive tutorial ride emphasizing even more the importance
of communication both ways whenever either rider has a problem, suggestion or input etc. There is no overreaction on parts. I needed a new chain and I got one.
Real simple. I will now also get the special excentric tool for adjusting tension and learn how to use it. I use toe clips, have used them for 20 years and I like them.
I wont argue theyy are better as they obviously are not .... at least for what I think are hi performance riders. I am not any kind of hi performance rider but my
perception is that toe clips are less headache, and more flexible with all kinds of shoes and riders for old fart recreational riders.