Chain length question/condundrum ...

[k-rod]

Howdy, y'all.

This may sound like a dumb question, but now that I'm in the final run of re-assembling my Romax, the time came to install my new (Sram pc-870) chain. I'm running a seven speed Shimano HG rear cluster, a 46/36/24 triple front ring combo, and a long-cage XT rear derailluer.

All the instructionals suggest running the new chain over both biggest sprockets (but not through the derailleurs), pulling the chain tight, noting the meeting point and then adding two links (an outer and an inner) plus the master link, for determining the appropriate lenggth for the chain.

Which i did. Cut it to allow two extra links plus the master, but when the chain is on the smallest sprockest front and back, the rear derailleur is in its full 'relaxed' mode and the chain sags down a fair bit with noticable slack. I know the bike couldn't be ridden in such a state, and I also know that the word is "you shouldn't ride a bike with the chain on both smallest sprockest" ... but when I look at both my KHS Pro-Montanna (same drive train) and my Kona Coiler (full susp), both of those bikes do not display an excessive amount of slack when the chain is positioned on both smallest sprockest (they would both be ridable in such a gearing position).

What should i do - take out two more links (one inner and one outer), so that it is then a tight fit from end to end plus one link (the master link only), rather than three, when looped around both biggest sprockets?

Any insightful and experienced advise will be largely appreciated, and thank you in advance!

 

[mattr]

A slack chain in gears that you never run is annoying, a chain that snaps is a safety concern.

I'd also be checking that you can run big/big on the other bikes as well.
Especially the full suss, chain growth can be a killer.

(I think someone on STW actually snapped a chain stay running a chain too short on his road bike)

 

[Radar]

Re:

An interesting conundrum, which I am sure has had you close to pulling you hair out.
Could be a daft question... don't s'pose you've still got the old chain to compare length to? That assumes you've had the current drive train combo working. If you haven't there might be some mileage in looking up the compatible cassette range/throw in the XT rear mech instructions.

Assuming all parts of the drivetrain are compatible, I've had this a couple of times.

On one occassion it was down to the rear mech, not the chain length. I adjusted the mech tension settings, gave everything a good spray lube, regreased and it was good to go. (Think of the rear mech moving in 3 directions, body can twist backwards as well as up, and then the arm movement. My mech body wasn't moving fully upwards nor twisting backwards - probably easier to see than describe). The other time was on my road bike, and no matter what I did couldn't resolve the issue. Ended up running a short chain (which would not run big/big).

 

[k-rod]

The rear mech is almost brand new, fully freshly greased and serviced (I'm being super meticulous on this build), and in perfect cosmetic and functioning order.

The ring set, rear derailleur, and rear cluster are exactly what I had been running before I de-constructed the bike, but ... unfortunately not knowing that this might be an issue or needed, I cut up the old chain in order to make myself a home-made chain whip (it actually turned out really nice!). While I can't be 110% certain, I'm pretty sure that the bike worked fine in all the gear/cluster combinations before, so that's why I am wondering what the best choice of actions would be.

 

[FluffyChicken]

Re:

Assuming the mech is OK.

If you run a you are you loose the loose gears, you can still pedal and be safe it just skips and charters a bit.

If you loose the two extras, you will more than likely at some point change into big-big. I know I do be it lazyness or not. The chain will get up there, probably not snap but will probably jam up there and likely pull the chain.

Up to you I know how I run and choose.


As for on the others, might have different chainstay lengths, ring size..?

 

[02gf74]

Re:

Hmm strange, a new long cage mech should take up the slack.

You put chain on over largest two sprockets, pulled it tight then marked the nearest cutting point to join it. Add two links but what is this master link you added?

How many extra links do yoy have from the cutting point?

 

[k-rod]

From the point where the two ends meet (when over both big sprockets) I added two links (one inner, and one outer), and cut the chain there. The SRAM PC-870 chain is joined with a clip-in master link, so that then ads a total of three links from the point where the two ends meet - the two links mentioned, and the master/joining link.

 

[scottproonly]

Re:

Try shifting it into big to big and see if the chain could be safely shortened at that point.if it can then this will cure your small to small slack
Kes

 

[k-rod]

Okay then, looks like I've got it sorted out. Seems the 'B-tension' screw was mal-adjusted so that the derailleur wouldn't swing round enough to take the slack when in full 'relaxed' mode. I've got the front and rear derailleurs connected and adjusted, and the chain length at meeting point plus two links plus the master-link appears to be spot on.

Now to throw the grips, bar ends, and tires on and take it for it's maiden ride ... (I'm sure she'll need some final fine-tuning adjustments).


Hoo-hah!!

 

[Radar]

Glad, you've got it working. Connecting/master links... I always count them as one of the 2 extra links, rather than them effectively being a third link. So if you have a bit of slackness you can lose another link.