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Timing chain problems

Kevin Smith2019-05-13 16:14:15

Hi, I've fitted new 38t chain rings and new chain with correct tension. it randomly derails, does anyone have experience of this and what they have done to resolve it please/

Richard Scrase2019-05-13 16:26:17

Hi Kevin, don't want to appear to teach my grandmother to suck eggs but have you checked the tension at different points in a complete circuit of the chain? A tight point might be the problem. Additionally, looking down onto the rings, does either of them have any dish / movement from the vertical?

All the best,


Chris Bishop2019-05-13 16:30:17

Not had any experience of it so can only make obvious suggestions, like are the rings in line?

Would width of chain make a difference? Our tandem has a nine speed timing chain, I think, but I put a wider chain on our previous tandem as I understand that the wider a chain is the less flex or sideways bend there is. 

2019-05-14 09:47:06

Do Tandems timings chain systems use wide narrow chainrings, like 1*10, or 1*11 MTBs?? as this would decrease the chance of a chain dropping off?

Chris Peachey2019-05-14 22:31:18

I think that the rings are either not in line or are not running true. I would not have thought that the width of the chain would cause the problem. Is your front eccentric loose? Turn the bike upside down and run the cranks in the normal drive direction to see what could be happening. Is a crank catching the chain?

Let us know the result please.

Chris Peachey (TC Technical officer)


Ruth Hargreaves2019-05-15 09:52:19

Hi Kevin

Sometimes we get tandems in for repair where the customer has fitted shifting rings, so middle rings with shifting ramps and pins and this causes the chain to derail. Cross over rings need to be non shifting, ie mono or inners.



JD Tandems

Kevin Smith2019-05-16 07:01:23

Thanks all,

Ruth, I was wondering that myself, yes they are middle rings, I’ll. change them. I’ve seen some stainless Surly rings. Do you have any suggestions?

Chris Bishop2019-05-16 09:11:59

This is more of a suplimentary question. Is there any merit in using track rings and/or chain? Is the wider size more rigid and less likely to derail, possibly over kill but even when the chain stretches or has some tighter and slacker points it is less likely to derail?

David Ross2019-05-16 09:20:54

I can recommend Surly chainrings in stainless steel. They have taller teeth and no shifting ramps or pins and of course being stainless last rather longer. Even then can be swapped front to back to get another lifetimes wear out of them.

The use of a 3/32 single-speed chain also helps - being less flexible - and also seems so far to last rather longer.

In terms of fitting, what I've found is that cranks and chainrings can be a little out-of-round or the chainring can be a slightly loose fit on the crank leading to eccentricity. By either carefully centreing the chainring - or rotating it on the crank - it is possible to achieve the best tension at all points in the rotation of the cranks and get rid of any really loose spots.

It does take patience - and you'll soon get fed up twiddling the 5mm allen key...


Dave & Sylvia

Ruth Hargreaves2019-05-16 09:40:25

Hi Kevin

I quite like Thorn's single rings, they are reversible so you can turn them around to increase the life. We would also routinely swop cross over rings from front to back during a service when they are showing signs of some wear. We use some FSA rings as cross over rings, whether I have them to fit your chainset I don't know as I don't know what PCD you have.



JD Tandems



Kevin Smith2019-05-16 15:47:47

Thanks Ruth, Thorn cranks, 5 bolt 110 BCD

Ruth Hargreaves2019-05-16 17:18:58

Hi Kevin

I'd buy the Thorn rings, give SJS a call if you need some advice but their website is pretty easy to navigate, our 38t crossover rings are a 104pcd.



JD Tandems