Chain Adjustment

[stutho]

Hi Cake,

It a really good question.  I wish I had a good reply. Most chain don't actually snap, instead one external plate 'pops' off a pin.  Chains that have being rejoined are often prone to this fault at the replaced pin.   

Just for kicks I decided to go and measure the extension in my chain after you last email.  The extension after 14,500km is 7/16th over 48 inches.  Thats less than 1/8th over 12 inches, I was expecting it to be a bit more! Here is the evidence!




Stutho

[Cake]

Thanks Stutho, i've learnt how a chain breaks - i had assumed there was some catastrophic metal failure involved rather than a slower prising effect going on.

Your measurements would seem to suggest that a pound-stretching 20000 Km out of your chain is a disticnt possibility!

[freddered]

The good thing about chains with Hubs-Gears is that they aren't subjected to lateral/twisting forces and they are extremely strong in tension even when worn.

In a purely theoretical world there is no reason for them to break until the pins/bearings have worn down significantly (by which time the chain would be flapping about dreadfully). 

I would have thought tons of force was required to snap a chain using just straight-line tensile forces.

Compare that to a derailleur chain being yanked and twisted sideways under a climbing load.  There would be considerable lateral/twisting forces exerted on the pins.  That's usually when they break.  I'm fairly kind to my derailleur mech when changing though and I've never had one break in over 30 years.

[stutho]

In a purely theoretical world there is no reason for them to break until the pins/bearings have worn down significantly (by which time the chain would be flapping about dreadfully). 

Agreed!!

[Hamish]

I have just tightened my chain for the second or third time.  It is now a little too tight I think.  There is very little deflection on pushing the chain downwards when the bike is not being peddaled.  However, seeing as the bottom of the chain is still a little loose under load, is the chain Ok or is it too tight? 

Hamish

[Cake]

Hi Hamish,

The chain tension sounds fine if there is a bit of slack when you load the pedals.  When my RT arrived from SJS the chain was very tight with no slack whatsoever under load - this soon changed after a few miles.  Those chaps know what they are doing, so yours should be fine.

My chain is looser than a wizards sleeve and it feels fine while pedalling - i'm going to leave it until it tells me otherwise, following the advice of Stutho, PH, Fredderred etc.

Gary.

[Hamish]

Thanks Cake

Yes my chain was very loose and was starting to slap about so I decided to tighten it.  I think it pedals better when it is  bit slacker.  It will soon loosten off anyway I'm sure.

Hamish

[Cake]

I adjusted the chain tension on my RT yesterday - i was waiting until i could feel a difference while pedalling before doing so, and the chain hinted at coming off after going over a bump at a particular point in the pedal stroke. 

Its the second adjustment and is 4100 miles since the last time i did it.  I use 3 in 1 to lube it and its a £3.49 KMC Z51 that came fitted from new with the bike.  All weather road use only.

Just thought it might be useful to have a couple of piccies of a loose chain and a tensioned one - both positions are extremely smooth, so leaving it all alone is fine from what my experience tells me!

[pdamm]

I had an interesting experience on a recent tour with chain tension.  I had been letting my chain get looser and looser, partly due to being lazy by nature and partly to see what would happen.  As a rough guess I would say it had about twice the sag than the first picture in Cake’s post.  Looking back I wish I had taken some measurements but I didn’t have a usable measure with me on the tour. 

On this particular day I had about 90km to ride on a mixture of dirt and sealed road.  The first 20km was on dirt and by far the roughest road of the day.  The chain was fine.  I then had 40km of sealed road – all was well.  The last 30 km was a mixture of sealed and dirt sections.  As soon as I hit the dirt sections the chain wouldn’t stay on!  It would derail every kilometre or so.  On the sealed sections it was still fine. 

If I wasn’t rushing to get to the post office at the next town before it closed I would have stopped and removed a link (it was due at this stage) and adjusted the tension.  What really surprised me was the sudden change in behaviour.  In the morning all was well in spite of the road being the worst for the day.  In the afternoon, after only 40km of riding later, the chain would barely stay put when I was on a dirt road.

As it happened I made it to the post office with ~20 minutes to spare and adjusted the chain tension the next day.

Peter

[geocycle]

While I am firmly in the 'don't tighten until it is about to fall off' camp to reduce the number of dents in the eccentric, it is different off road.  The only times my chain has come off is when riding offroad.  I also had the experience of the chain lifting at the same time the chain wheel grounded on a rock causing 4 links to be broken. 

[Chadlington]

Cake,

I don't suppose you had a picture of the eccentric taken at the same time before and after did you? I'm in the "don't adjust camp" too because it seems like the safer option for a new owner concerned not to damage things with un-needed adjusting. However, I too had a couple of odd things that might be chain tension related and i'm certainly more slack than the book says I should be.

For anyone out there with a Rohloff chain, is there a newbie's guide to joining/breaking the thing? Interested in case the eccentric won't take up all the slack.

Thorn advised to adjust after 5m and 50m I think - I'm past both those easily.

[Cake]

Chadlington, sorry, i didn't take pics of the ebb whilst i was at it.  I do know that despite the chain being very slack (it seemed slacker than it looks in the photo!) the ebb only rotated by a very small amount (about 30 - 40 degrees) - the bottom bracket is now directly over the set screws.

I split the chain last time it needed adjusting to discover whether or not i could use a half-link for adjustment  - i would think there has to be quite a lot of chain wear before removing a link is required (when the ebb is at maximum adjustment probably).  Other people have done this, so i sure they will tell all!

Geocycle - absolutely, my chain would have come off long ago had i gone off road.  I bet that chainwheel grounding sent a shudder through your arms! Ouch!

Gary.

[julk]

For anyone out there with a Rohloff chain, is there a newbie's guide to joining/breaking the thing? Interested in case the eccentric won't take up all the slack.

Chadlington,
I use a Rohloff chain and bought a spare which is longer than I need. I removed the extra links with a hand held chain breaker and carry them as a small loop of chain with me in case a chain repair is needed.

Just treat it like a normal (not Shimano) chain and drive the pin as far out as you need. Right out to remove a link, still just sticking in the side plate for a rejoin.

The rejoined chain link has no need to be slackened up a bit for sideways flexibility, another benefit of a Rohloff!

Julian

[freddered]

Last time I had used up all the EBB adjustment ychain was still slightly too short to rejoin after removing a link.  i.e. The EBB adjustment is slightly less than a link.

This time I'm letting the chain go slacker before I remove a link.

PS.  I use a Power link to join it.

Next chain I buy will be made up of half-links.

[Chadlington]

Well, I did it. Lots of reading the manual and checking over and over but the EBB adjustment is done.

When I removed the screws, there was hardly any mark on the EBB shell itself at the bottom of the hole.
The bike's only three months old, but met the recommendation from the guy at Thorn who sold me the bike to adjust after the Rohloff chain after 50m.
The EBB turned flawlessly and it was easy to see how the chain tension changed.
I set the tension such that the T1-T2 measures in the book were a bit less than when I first got the bike. Given the chain had gone really quite slack, like Thorn said the Rohloff chain would, it seemed reasonable.
The screws went back in but didn't get to the 10Nm before I felt as though they were probably back where they should be.
I added some threadlock for good measure.

I'll monitor on a ride tomorrow, and will make a small mark so I can tell if there's any movement in the EBB (After about a month of ownership, there was a creaking noise from the EBB and I tightened the screws then.)

Thanks for all the advice, much appreciated.