Trying not to cock this up (again).
The instructions say
For full suspension bikes, check the length of the chain with the suspension in its fully extended position.
I take it this means fully extended shock (ie the lockout position), rather than with the chainring and cassette at their maximum distance apart in the stroke?
TIA
Is read that as in the position where the chainstays are at their longest.
Hence my problem. It's a bit ambiguous 🙂
The argument against that is that the guide stipulates adding more links for FS than for a hardtail, which doesn't seem logical if you were taking the measurement already at the point of maximum possible distance with no further chain growth possible.
In fairness when I’ve sized my chain on Shimano 12 speed on my full suss I’ve just done it with the bike in its normal unsagged position and made shore it doesn’t look too short I’m then51 tooth cog. All been fine with the b screw setup correctly.
Although I dislike Shimano chains as they are noisy / skippy in wet / grit / mud. Sram xx1 chains all the way - run way better. And oilslick / gold 🥰
Most bikes have a longest chain length when the shock is fully compressed. So measure it there.
Not really as in its most extended position the rear wheel axle is furthest from it's resting position.
In this position the shock may not be fully compressed due to varying axle paths of different suspension designs, the video on how to fit a SRAM 12 speed chain explains it very well the important bit is 6:30min into the vid. Then follow the Shimano guide for how long the chain should be, job done.
Most bikes have a longest chain length when the shock is fully compressed. So measure it there.
My only concern was that the Shimano instructions here:
https://si.shimano.com/en/dm/MARD001/Checking_the_chain_length
already appear to account for chain growth with the difference between HT and FS link numbers. (5-6 links for FS compared with 4-5)
I take it as they have allowed long chain for FS than hardtail so some chainstay growth has been accounted for so chain length is to be done with suspension fully extended (not fully compressed), and then that check 'A' is at full extension (of the chainstay length) noting full extension of the dimension, not the suspension.
So basically, size with bike in the stand (suspension fully extended), and after sizing and fitting do a check of chain stay at maximum growth to check enough slack though max length of chainstay.
Thanks! Just wanted to sense check before I start cutting chains.
you can always do a check with the chain fully routed and just use a cable tie or wire to join chain whilst moving suspension through full travel.
In that SRAM vid linked to above they say to allow more overlap for hardtail than full sus. Which seems a bit strange to me.
The best way to do it is just to take out a shock bolt and move it through the travel. The rules will get you close, sometimes it'll get you exactly the same answer but this way is foolproof
I remember seeing that some suspension designs actually have an s shaped compression curve just to be even more annoying. I'd fit the chain full length and then check let the air out of the shock and compress the suspension just to check. It's dead easy to take a link or two out if you think that the chain is too long.
Has been discussed before, a while ago 😉
https://singletrackworld.com/forum/topic/what-chain-length-for-full-suspension-bike/
@didnthurt problem with that other thread is that is has the usual big-big plus two links, which was fine in the olden days, but this is not suitable for current 12sp shimano setup.
But def worth a check though full suspension movement.
Done it according to Shimano's method, mech is back against the stop and not under tension in the 10t, so I suspect chain is a fraction too long. But I'll give it a go to see.
give it a go, there is very little tension when in 10t anyway. what is it like at sag point?
you do 5 or 6 links + ql?
also check the B adjust to check alignment with cage mark / big sprocket tooth, as that can take slack up if not fully adjust out to the line
the other thing i found is that if you are using 10-45 12 speed and short cage 12sp mech (XT or XTR) the shimano guide does not account for the shorter cage so you need to take a couple pf links out.
Yeah, 5 links, it starts to pull forward with a bit of sag (but I do have it locked out a fair bit too). B-screw is OK, but I'll have a play with it tomorrow.
In that SRAM vid linked to above they say to allow more overlap for hardtail than full sus. Which seems a bit strange to me.
Probably because the likelihood of you bottoming out the suspension while in the lowest gear is incredibly slim, so the slightly shorter chain stops you having loads flapping about in higher gears. I did think it strange when I fitted a new Eagle 12 chain (cassette and ring) to a new to be HT, but it works, shifts well and runs quietly.