Setting up rear derailleur and chain length
strauss_jon
Posts: 39
Hi all
Just trying to set up my single xt m8000 rear derailleur and chain. Couple of issues / points.
I've read that there's 2 typical ways to figure out the chain length. First is to wrap chain around chain ring and largest sprocket without going through the derailleur and removing 2 links - approx. Second is going through the derailleur and on the smallest sprocket. I thought that as they're both recommended options, the lengths would end up being at least similar. You can see from the 2 pics below that the big sprocket without the derailleur method requires the removal of a lot more links than the small sprockets method. Confusing. Which one out of the 2?
Also, i've read that the rear derailleur chain clearance when on the smallest sprocket should be minimal but not rubbing.Is what i've done below excessive? This was based on removing 2 links using method 2 above. Looks like i've removed 1 link too much - what do you reckon?
Lastly...how i can experiment with different chain lengths without having to use up multiple connecting pins? I don't think they can be inserted / removed / re-inserted can they? I'd prefer not to have to keep breaking them as they're £8 a set of 3. At the moment i stick in a pin without 'seating it in', pedal for a couple of revs, pack pedal (so chains keeps falling down to smaller cogs as they do?) and start again. Slow progress.
Cheers!
Just trying to set up my single xt m8000 rear derailleur and chain. Couple of issues / points.
I've read that there's 2 typical ways to figure out the chain length. First is to wrap chain around chain ring and largest sprocket without going through the derailleur and removing 2 links - approx. Second is going through the derailleur and on the smallest sprocket. I thought that as they're both recommended options, the lengths would end up being at least similar. You can see from the 2 pics below that the big sprocket without the derailleur method requires the removal of a lot more links than the small sprockets method. Confusing. Which one out of the 2?
Also, i've read that the rear derailleur chain clearance when on the smallest sprocket should be minimal but not rubbing.Is what i've done below excessive? This was based on removing 2 links using method 2 above. Looks like i've removed 1 link too much - what do you reckon?
Lastly...how i can experiment with different chain lengths without having to use up multiple connecting pins? I don't think they can be inserted / removed / re-inserted can they? I'd prefer not to have to keep breaking them as they're £8 a set of 3. At the moment i stick in a pin without 'seating it in', pedal for a couple of revs, pack pedal (so chains keeps falling down to smaller cogs as they do?) and start again. Slow progress.
Cheers!
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Comments
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Don't forget and extra chain required by the movement of the suspension.
Little ring on the front, little cog on the back, move the suspension until the chain becomes the slackest and just take enough links out to have the chain under tension and not have the lower chain span bumping into the top pulley.
Single front cog is no different, just far less critical to chain length and you can run it a little shorter if you like to keep the chain under higher tension in the little rear cog as you have to run this gear, unlike a double where you don't normally run that combo.
Run through all gears to check it isn't too short and that you have exceeded the derailleur capacity.
All else fails, go to the shimano tech docs website and read all about it.0 -
Think he's going to struggle to get the suspension to compress on that hardtail, don't you? ;-)Don't forget and extra chain required by the movement of the suspension.
Little ring on the front, little cog on the back, move the suspension until the chain becomes the slackest and just take enough links out to have the chain under tension and not have the lower chain span bumping into the top pulley.
Single front cog is no different, just far less critical to chain length and you can run it a little shorter if you like to keep the chain under higher tension in the little rear cog as you have to run this gear, unlike a double where you don't normally run that combo.
Run through all gears to check it isn't too short and that you have exceeded the derailleur capacity.
All else fails, go to the shimano tech docs website and read all about it.2015 Canyon Nerve AL 6.0 (son #1's)
2011 Specialized Hardrock Sport Disc (son #4s)
2013 Decathlon Triban 3 (red) (mine)
2019 Hoy Bonaly 26" Disc (son #2s)
2018 Voodoo Bizango (mine)
2018 Voodoo Maji (wife's)0 -
It's a general how to, I don't think that single ring is going to cause and derailleur capacity problems either...
So many of these so called formulas for chain length are simply just a starting point.
The only things that matter are that the chain is not too stretched on the big big and not run out of tension or bump the chasin into the pulley on the small small.
Looser is always better than tighter.
Beware suspension changes things.
If you cannot achieve that, then start looking at derailleur capacity to see what is wrong.0 -
Your premise is wrong, round the two largest and add 2 links, not remove.0
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Or even overlap by two links (minimum), adding or removing is irrelevant as you don't know how much too long or short the chain is to start with.Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0
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Cheers for your replies, just got back and not had a chance to try anything. I'm back on wed eve and will have a play then. So ill keep this post open if you dont mind.
Pointless message i know...just don't like to sound like I'm ungrateful by not replying
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The big/big plus two will often bring you up short with long cage derailleurs.
Even short cage road derailleur will come up short with 28 to 32 rear cogs on board.
If you have an spare old removeable chain link, cut the chain a bit too long and fit it, run through all the gears and figure out the length needed by folding it over itself.
Remove old link and then shorten and use joiner pin or fit a nice new snappy link.0 -
Rubbish, I think Shimano know better than you what size the chain should be seeing as how they make the mech, the cassette, the chain and the crankset in many cases.The big/big plus two will often bring you up short with long cage derailleurs.
Even short cage road derailleur will come up short with 28 to 32 rear cogs on board.
If you have an spare old removeable chain link, cut the chain a bit too long and fit it, run through all the gears and figure out the length needed by folding it over itself.
Remove old link and then shorten and use joiner pin or fit a nice new snappy link.
Big and Big + 2 works perfectly, the only caveat is that on an FS with moderate chain growth you should do it with the suspension at the worst height.
Have the chain too long and you reduce the capacity of the rear mech!Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
Derailer cage length does not dictate what length chain is needed for safe operation. The chain must be sized so it can run in the big/big combo because, if it can't and you accidentally shift into it, you will cause a hell of a lot of expensive damage if you are pushing hard. The derailer, no matter what cage length (though it must be specced to cope with the large sprocket size ie max tooth rating - or you may need a longer B tension screw or adapter) will stretch enough if the chain is measured as per Shimano and SRAM guides.
The cage length is about capacity and the ability to run all gears without slack once the above chain length is determined. Slack doesn't cause nearly as many problems as the chain being too tight - both of these gears are not desirable to use, but I see no sense in sizing the chain to allow the small/small combo which causes no damage if this gear selected, over sizing for the big/big, which will cause a lot of damage if selected. Why choose one over the other, if you don't have a mech that can't handle the extremes?0 -
Test0
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The Rookie wrote:
Rubbish, I think Shimano know better than you what size the chain should be seeing as how they make the mech, the cassette, the chain and the crankset in many cases.The big/big plus two will often bring you up short with long cage derailleurs.
Even short cage road derailleur will come up short with 28 to 32 rear cogs on board.
If you have an spare old removeable chain link, cut the chain a bit too long and fit it, run through all the gears and figure out the length needed by folding it over itself.
Remove old link and then shorten and use joiner pin or fit a nice new snappy link.
Big and Big + 2 works perfectly, the only caveat is that on an FS with moderate chain growth you should do it with the suspension at the worst height.
Have the chain too long and you reduce the capacity of the rear mech!
Shimano also specifies a minimum chain stay length.
Many bikes run shorter than this.
If you size with +2 links the chain runs at a very oblique angle and twisting the rear mech.
Further more the chain will tend to run from one side of the bottom pulley to the other side of the top pulley due to this side force.
This pushes the floating top pulley hard up against one side and messes with the indexing and prevents the pulley from floating. Size to the max length and the angle decreases dramatically.
+2 is simply a rough guideline and there is very often a better choice.
Also if you size on the long side, then if the back wheel gets changed for one with a larger cluster then you won't rip the derailleur off.0 -
The Rookie wrote:
Rubbish, I think Shimano know better than you what size the chain should be seeing as how they make the mech, the cassette, the chain and the crankset in many cases.The big/big plus two will often bring you up short with long cage derailleurs.
Even short cage road derailleur will come up short with 28 to 32 rear cogs on board.
If you have an spare old removeable chain link, cut the chain a bit too long and fit it, run through all the gears and figure out the length needed by folding it over itself.
Remove old link and then shorten and use joiner pin or fit a nice new snappy link.
Big and Big + 2 works perfectly, the only caveat is that on an FS with moderate chain growth you should do it with the suspension at the worst height.
Have the chain too long and you reduce the capacity of the rear mech!
Shimano also specifies a minimum chain stay length.
Many bikes run shorter than this.
If you size with +2 links the chain runs at a very oblique angle and twisting the rear mech.
Further more the chain will tend to run from one side of the bottom pulley to the other side of the top pulley due to this side force.
This pushes the floating top pulley hard up against one side and messes with the indexing and prevents the pulley from floating. Size to the max length and the angle decreases dramatically.
+2 is simply a rough guideline and there is very often a better choice.
Also if you size on the long side, then if the back wheel gets changed for one with a larger cluster then you won't rip the derailleur off.0 -
The Rookie wrote:Rubbish, I think Shimano know better than you what size the chain should be seeing as how they make the mech, the cassette, the chain and the crankset in many cases.
Big and Big + 2 works perfectly, the only caveat is that on an FS with moderate chain growth you should do it with the suspension at the worst height.
Have the chain too long and you reduce the capacity of the rear mech!
Shimano also specifies a minimum chain stay length.
Many bikes run shorter than this.
If you size with +2 links the chain runs at a very oblique angle and twisting the rear mech.
Further more the chain will tend to run from one side of the bottom pulley to the other side of the top pulley due to this side force.
This pushes the floating top pulley hard up against one side and messes with the indexing and prevents the pulley from floating. Size to the max length and the angle decreases dramatically.
+2 is simply a rough guideline and there is very often a better choice.
Also if you size on the long side, then if the back wheel gets changed for one with a larger cluster then you won't rip the derailleur off.0 -
Posting three times doesn't make it right....
They do, but few bikes have a CS shorter than that so not really relevant to your bad advice, it's how Shimano and SRAM and park tools state to do it, but I'm sure you know better than all of them right?Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
Actually Shimano shows two procedures.
The other one is to put it in big front small rear and the rear derailleur should have the pulleys lined up vertically.
They are both a guide, a starting point, that's all.0 -
when doing one of my bikes, it says use the vertical pully method, unless the biggest rear sprocket is 32+ then use the big/big + 20
