Had an accident - chain length
Had an accident - chain length
Hello
Specialized Rockhopper Sport, Acera 8sp rear mech.
So I'm trying to work out the correct chain length, without the old one as a reference, but different sites seem to be telling me different things.
What I've got so far:
Chainstay length is 435mm (17.125")
34T cassette
44T chainring
So, 17.125 x 2 = 34.250"
34/4 = 8.5"
44/4 = 11"
34.250" + 8.5" + 11" = 53.75" (rounded to 54") plus 1" = 55" / 110 links.
Here's the complication - my rear mech has 13T guide/tensioner pulleys - do I need to add any chain length on to account for that?
This site tells me 110 links also: https://www.alpinetrek.co.uk/chain-length-calculator/ but it also says to allow extra if the jockey wheels are bigger than 10T, which they are.
Even if I scrap all this and use the Big/Big +1" measuring method, I still have these two oversized pulleys I might need to take into consideration. Something in my mind is telling me to start at 112 links and take it from there.
Thoughts?
Specialized Rockhopper Sport, Acera 8sp rear mech.
So I'm trying to work out the correct chain length, without the old one as a reference, but different sites seem to be telling me different things.
What I've got so far:
Chainstay length is 435mm (17.125")
34T cassette
44T chainring
So, 17.125 x 2 = 34.250"
34/4 = 8.5"
44/4 = 11"
34.250" + 8.5" + 11" = 53.75" (rounded to 54") plus 1" = 55" / 110 links.
Here's the complication - my rear mech has 13T guide/tensioner pulleys - do I need to add any chain length on to account for that?
This site tells me 110 links also: https://www.alpinetrek.co.uk/chain-length-calculator/ but it also says to allow extra if the jockey wheels are bigger than 10T, which they are.
Even if I scrap all this and use the Big/Big +1" measuring method, I still have these two oversized pulleys I might need to take into consideration. Something in my mind is telling me to start at 112 links and take it from there.
Thoughts?
Last edited by Darkman on 18 Apr 2021, 8:48pm, edited 1 time in total.
Re: Had an accident - chain legnth
KISS: Big- Big add two links has never failed me.
I fail to see what the pulley size has to do with it.
I fail to see what the pulley size has to do with it.
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Re: Had an accident - chain legnth
You can also do small/small (running the chain through the rear derailleur) and take enough length out that there is a bit of a gap between the guide pulley/cage and the bottom run of chain.
Last edited by gregoryoftours on 18 Apr 2021, 5:07pm, edited 1 time in total.
Re: Had an accident - chain legnth
If I knew how to ride a bike, safely, I'd do it every time.
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Re: Had an accident - chain legnth
Don't faff about measuring chainstay length, that youtube clip is the best way! My old man showed me the YouTube method almost 50 years ago and it's always worked for me.
Re: Had an accident - chain legnth
+1 - i've done it that way for - well all my bike looking after career, the only time i've had chain length issues is when i haven't used that method for some reason.gregoryoftours wrote: ↑18 Apr 2021, 2:03pm You can also do small/small and take enough length out that there is a bit of a gap between the guide pulley/cage and the bottom run of chain.
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!
Re: Had an accident - chain legnth
Big to Big + a link. Guarantees that the chain won't jam up if you select big ring to big sprocket.
You'll never know if you don't try it.
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Re: Had an accident - chain legnth
But do these methods take account of long cage mechs, or mechs with a large jockey wheel?
Re: Had an accident - chain legnth
Big sprocket to big chain ring plus one is minimum - if its a tourer you bang as many more links in as you can even allowing the chain to become slack in small to small. Because the more links the less wear and it gives you plenty of spare links incase of breakage.
If your racing & more concerned about weight keep to the minimum but never less (you need to access all combinations in the event of a mistaken shift). no need for fancy formulas & measuring chain stays.
If your racing & more concerned about weight keep to the minimum but never less (you need to access all combinations in the event of a mistaken shift). no need for fancy formulas & measuring chain stays.
Cheers
J Bro
J Bro
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Re: Had an accident - chain legnth
The assumption seems to be that pulley size and cage length isn't relevant because the chain passing almost straight through the derailleur when it pulls fully forward, so the two links accounts for the deviation? I believe cage length and pulley size make little difference to that path.fastpedaller wrote: ↑18 Apr 2021, 6:29pm But do these methods take account of long cage mechs, or mechs with a large jockey wheel?
It would be easy to try it with four links first and see.
Re: Had an accident - chain legnth
That will work if the rear mech has the capacity for the system in use, which should be the case if the bike has the original spec. However it could well lead to disaster if the rear mech doesn't have the capacity for the system in use. This is the case on two of my bikes and is the reason why a minimum chain length should be Big/Big plus 2 links.foxyrider wrote: ↑18 Apr 2021, 3:31pm+1 - i've done it that way for - well all my bike looking after career, the only time i've had chain length issues is when i haven't used that method for some reason.gregoryoftours wrote: ↑18 Apr 2021, 2:03pm You can also do small/small and take enough length out that there is a bit of a gap between the guide pulley/cage and the bottom run of chain.
Before anyone criticises me for running gears that don't work let me assure you that they do. On one of my bikes I'm running a short Ultegra mech with 50/34 and 11-32 (a GS mech would eliminate slack on small/small) and on the tandem there isn't a rear mech available that will cope with the capacity of the system without slack on small/small.
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Re: Had an accident - chain length
Ah yes you are right. Don't use short/short if there's any doubt about the rear mech's total capacity being exceeded. Could be risky!
Re: Had an accident - chain legnth
Absolutely spot on.
If I put mine on Moulton big big plus one, it's floppy and loose on small small ....................... which means if I use Method2 in that YouTube movie, I would jam up on big big.
Exactly!gregoryoftours wrote: ↑19 Apr 2021, 8:31am Ah yes you are right. Don't use short/short if there's any doubt about the rear mech's total capacity being exceeded. Could be risky!
Mick F. Cornwall
Re: Had an accident - chain length
Just try 112 first in big to big, then you will be able to work out what will happen if you take another link out, if it would still work at 110 then take another link out
Re: Had an accident - chain length
Worst case scenario for a too tight chain is:
It wont go on and the pedals jam
It tries to go on but bends the chain ring over
It goes on & buckles / collapses the chain stay.
It breaks the back axle as your effectively pulling from the middle of it when on the big sprocket.
If your lucky the chain might break first.
Worse case for a slack chain is it comes off. Which although it can have unfortunate consequences the risk is no worse than any other time the chain comes off.
It wont go on and the pedals jam
It tries to go on but bends the chain ring over
It goes on & buckles / collapses the chain stay.
It breaks the back axle as your effectively pulling from the middle of it when on the big sprocket.
If your lucky the chain might break first.
Worse case for a slack chain is it comes off. Which although it can have unfortunate consequences the risk is no worse than any other time the chain comes off.
Cheers
J Bro
J Bro