Author Topic: Correct chain tension for my Raven  (Read 3235 times)

ChrisBarrett

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Correct chain tension for my Raven
« on: March 06, 2021, 02:08:00 PM »
It probably on here somewhere but I'm struggling to find. I'm going to adjust my chain on my Raven, what is a good tension to set it to? I see in the owners manual it says adjust when the play reaches 40mm as per the diagram but cant see a measurement to set it to.
Any help appreciated.

PH

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Re: Correct chain tension for my Raven
« Reply #1 on: March 06, 2021, 03:31:32 PM »
The advice somewhere, either the Rohloff manual or some Thorn literature, is for there to be about 10mm in either direction at the midpoint on the bottom run of chain - That is if you push it up and down there's about 20mm between the extremes.
In my experience, anywhere less tight than a drum and less slack than falling off will be fine, when mine was new I'd be a bit excessive about it, now far less so.  if anything it runs a bit better slacker.

ChrisBarrett

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Re: Correct chain tension for my Raven
« Reply #2 on: March 06, 2021, 03:51:56 PM »
Thanks so much. I was worried about having it too tight.

JohnR

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Re: Correct chain tension for my Raven
« Reply #3 on: March 06, 2021, 06:49:54 PM »

j-ms

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Re: Correct chain tension for my Raven
« Reply #4 on: March 06, 2021, 07:59:58 PM »
I keep my chains as loose as possible.  The ten centimeters both ways sounds about right to start off with ... but then don't tighten again until the chain falls off or slips under pressure.

UKTony

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Re: Correct chain tension for my Raven
« Reply #5 on: March 06, 2021, 09:05:30 PM »
until the chain falls off or slips under pressure.
Personally I wouldn’t risk damage to flesh and bone or paint and steel by waiting until this happens.

Andre Jute

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Re: Correct chain tension for my Raven
« Reply #6 on: March 06, 2021, 11:25:25 PM »
The thing to consider with the Rohloff handbook is that whatever they tell you to do is pretty much a rule, even if they don't surround it with grim warnings. So, if the chain is too tight, I'd worry about it doing harm to the Rohloff box. I start my chains with a minimum of 10mm play on each run of the chain*, taken at about mid chain, as has already been suggested in this thread, and then just let it run until the end of life of the chain. In ten years I've had only two chain drops, and in one of those the problem was caused by a branch lying on the road getting between the spokes of the wheel. In both instances the Chainglider saved the irreplaceable historic coachwork on my bike.

A chain has to be considerably slacker than 20mm total play before you can remove a link, so 20mm is really the first stop between the minimum amount of slack and the point where you can remove a link and still have 20mm Rolloff-Regulated slack. If you're a compulsive obsessive I suppose you can mess with half-links and keep a reasonably constant slack close by and on the right side of 20mm without wrecking the adjustments on your eccentric bottom bracket by impressing a channel rather than widely separated pits. But 20mm is clearly a minimum, not a fixed quantity, and has wide latitude on the higher side, probably limited more by sensible use of the bottom bracket than by the chain dropping off easily.

It's one of those things that after a while you cease to worry about because you come to understand that, as long as you follow a few non-critical rules like this, your Rohloff will probably be passed on to your grandchildren.

* Eyeballed: there's no point in landing in divorce court for getting dirty chain oil on your wife's hemming measure.

John Saxby

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Re: Correct chain tension for my Raven
« Reply #7 on: March 07, 2021, 09:00:51 PM »
On my Raven, I follow Thorn's advice and use measurements as follows:

First, mark your chainstay's midpoint (centre point of crank to centrepoint of Rohloff hub).  (I use a thin strip of black electrician's tape.)

Then, find your chain's tight spot and move that to the midpoint of the chain. (I just put a gloved finger at midpoint on the lower side of the upper chain run, raising the chain to take out its slack, and spin the cranks.  The tension on my finger tells me where the tight pot is.)  (Note here: That used to be my drill. But since I bought two lovely 36T alloy chain rings from Rivendell Bike Works, my chains no longer have tight spots.)

I follow Thorn's recommendation of 40 mm this way:

    >  Using my finger & thumb, I spread the upper & lower runs to the maximum vertical play between the two runs of the chain, and use my tape to measure the gap betw the lower edge of the top run and the upper edge of the bottom run.  (When I've got things right, that's usually around 110-120 mm on my setup.  It's Thorn's "T1" measurement.)

    >   Then, I squeeze the two runs together to get the minimum vertical play, again betw the lower edge of the top run and the upper edge of the bottom run. (Usually around 70-80 mm, Thorn's "T2".)

    >   Adjust the eccentric to give yourself more of less play.

A couple of further notes from experience:

    >  I wait until I have at least 60 mm of play before readjusting the EBB to reduce the play in the chain to 40 mm +/-

    >  Over the past 12 -18 months, I have had some irritatin' creaks and ripply noises in my chain. I finally got rid of them by (i) cleaning and renewing the ant-seize on my EBB, and (ii) tightening my EBB fixing screws to the maximum allowed (150 inch-lbs.)

Hope that's helpful, and good luck!

PH

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Re: Correct chain tension for my Raven
« Reply #8 on: March 07, 2021, 10:07:52 PM »
Thorn's guidance is on page 12 of http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf .
Thanks for that, I don't recognise it, but it may be where my 20mm comes from, 20 on the one run being pretty much the same as 40 across the two.
That is a little ambiguous though, saying don't adjust at less than 40mm, rather than adjust it to that.  It doesn't give any guidance on how tight the tightest should be, other than saying too tight is a bad thing. I think I'll stick to using that 20 on the bottom run as a starting point.  I can only remember having a chain unship once and that was a slipped EBB, going back to another thread, perfect chainline helps of course, as does a decent chainring.

PH

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Re: Correct chain tension for my Raven
« Reply #9 on: March 07, 2021, 10:12:07 PM »
The ten centimeters both ways sounds about right to start off with ... but then don't tighten again until the chain falls off or slips under pressure.
:o :o :o
With ten centimetres the biggest risk would be it dragging along the ground  ;)

j-ms

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Re: Correct chain tension for my Raven
« Reply #10 on: March 08, 2021, 03:25:59 PM »
Quote
With ten centimetres the biggest risk would be it dragging along the ground
Well spotted!  Maybe it's not just my chain that has fallen off. :-[ :-[ :-[

Rouleur834

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Re: Correct chain tension for my Raven
« Reply #11 on: May 28, 2021, 09:09:07 AM »
On my Raven, I follow Thorn's advice and use measurements as follows:

First, mark your chainstay's midpoint (centre point of crank to centrepoint of Rohloff hub).  (I use a thin strip of black electrician's tape.)

Then, find your chain's tight spot and move that to the midpoint of the chain. (I just put a gloved finger at midpoint on the lower side of the upper chain run, raising the chain to take out its slack, and spin the cranks.  The tension on my finger tells me where the tight pot is.)  (Note here: That used to be my drill. But since I bought two lovely 36T alloy chain rings from Rivendell Bike Works, my chains no longer have tight spots.)

I follow Thorn's recommendation of 40 mm this way:

    >  Using my finger & thumb, I spread the upper & lower runs to the maximum vertical play between the two runs of the chain, and use my tape to measure the gap betw the lower edge of the top run and the upper edge of the bottom run.  (When I've got things right, that's usually around 110-120 mm on my setup.  It's Thorn's "T1" measurement.)

    >   Then, I squeeze the two runs together to get the minimum vertical play, again betw the lower edge of the top run and the upper edge of the bottom run. (Usually around 70-80 mm, Thorn's "T2".)

    >   Adjust the eccentric to give yourself more of less play.

A couple of further notes from experience:

    >  I wait until I have at least 60 mm of play before readjusting the EBB to reduce the play in the chain to 40 mm +/-

    >  Over the past 12 -18 months, I have had some irritatin' creaks and ripply noises in my chain. I finally got rid of them by (i) cleaning and renewing the ant-seize on my EBB, and (ii) tightening my EBB fixing screws to the maximum allowed (150 inch-lbs.)

Hope that's helpful, and good luck!

Hello - apologies for revisiting this one. Newbie here and I've been looking for guidance about chain tension for my Mercury Mk3. I saw the guidance in the Thorn handbook and was looking for a little more detail which you have provided. Having just switched from a derailleur system I'm wondering if a simple, in my case Park Tool, chain checker could be used. Possibly a naive question but why is the recommended method as it is and not simply measured from link to link. Thanks in anticipation. Ray.

Aleman

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Re: Correct chain tension for my Raven
« Reply #12 on: May 28, 2021, 09:16:52 AM »
I use the park tool checker to determine the optimal time to change the chain, just as I do on our derailleur bikes. However, I don't worry about it. if the chain gets so stretched that it starts jumping off the chain rings, then I can adjust the eccentric to get me to a bike shop / home. If I was on a long tour I would have probably fitted a new chain anyway as a precaution. The other thing to remember with a Rohloff is "Looser is better" ... until the chain jumps off the chainring ... then its time to adjust it with the ECC

PH

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Re: Correct chain tension for my Raven
« Reply #13 on: May 28, 2021, 09:41:13 AM »
Possibly a naive question but why is the recommended method as it is and not simply measured from link to link. Thanks in anticipation. Ray.
It's two different things, for two different purposes.  One is measuring chain wear to determine if it's worn to the extent where it wears other components and the other measuring chain tension to determine if it needs adjusting to stop it unshipping.
Re the first, chain wear - The advice in the "Living with a Rohloff" pdf booklet, is to not bother trying to prolong the other components by changing chains that still have plenty of usable life, but instead judge the wear by the sprocket and replace chain and change/reverse the chainring and sprocket all at the same time.
There are differing opinions, the pros and cons are possibly about equal, but all new to all worn is simpler than trying to keep new components matched with worn.
It is a very different story with a derailleur, the worn chain effects shifting, the sprockets are worn differently and the poor ones will skip while others are fine.  You might be surprised just how worn a single chainline can get before needing anything replaced.
« Last Edit: May 28, 2021, 09:44:03 AM by PH »

JohnR

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Re: Correct chain tension for my Raven
« Reply #14 on: May 31, 2021, 08:35:50 AM »
Hello - apologies for revisiting this one. Newbie here and I've been looking for guidance about chain tension for my Mercury Mk3. I saw the guidance in the Thorn handbook and was looking for a little more detail which you have provided.
It's quite simple. Get the tension so that distance between lifting the midpoint of the chain up and pushing it down is about 4cm. That may look loose compared to what you are used to but Thorn will have accurately set up the chainline to be straight so there's no reason for the chain to want to jump off. If the chain is too tight then there's the risk of extra load on the bearings in the Rohloff hub.

You will find that a very small rotation of the eccentric bottom bracket will cause a significant change in the chain tension as the movement affects the chain twice. It's worthwhile fiddling with the chain tension, if only to discover how the system works - better to discover this at home rathr than on the road although the likelihood of your Mercury getting chain problems is very small.