Had an accident - chain length

For discussions about bikes and equipment.
Darkman
Posts: 242
Joined: 30 Aug 2019, 8:46pm

Had an accident - chain length

Post by Darkman »

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?
Last edited by Darkman on 18 Apr 2021, 8:48pm, edited 1 time in total.
User avatar
Paulatic
Posts: 7804
Joined: 2 Feb 2014, 1:03pm
Location: 24 Hours from Lands End

Re: Had an accident - chain legnth

Post by Paulatic »

KISS: Big- Big add two links has never failed me.
I fail to see what the pulley size has to do with it.
Whatever I am, wherever I am, this is me. This is my life

https://stcleve.wordpress.com/category/lejog/
E2E info
gregoryoftours
Posts: 2234
Joined: 22 May 2011, 7:14pm

Re: Had an accident - chain legnth

Post by gregoryoftours »

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.
Percy
Posts: 18
Joined: 29 Mar 2021, 8:21pm

Re: Had an accident - chain legnth

Post by Percy »

Darkman wrote: 18 Apr 2021, 12:42pm 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.
Thoughts?
It's really quite simple.

https://www.youtube.com/watch?v=Vg2SoOOrpE8
If I knew how to ride a bike, safely, I'd do it every time.
philvantwo
Posts: 1730
Joined: 8 Dec 2012, 6:08pm

Re: Had an accident - chain legnth

Post by philvantwo »

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.
User avatar
foxyrider
Posts: 6044
Joined: 29 Aug 2011, 10:25am
Location: Sheffield, South Yorkshire

Re: Had an accident - chain legnth

Post by foxyrider »

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.
+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.
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!
User avatar
cycleruk
Posts: 6065
Joined: 17 Jan 2009, 9:30pm
Location: Lancashire

Re: Had an accident - chain legnth

Post by cycleruk »

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.
fastpedaller
Posts: 3435
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: Had an accident - chain legnth

Post by fastpedaller »

But do these methods take account of long cage mechs, or mechs with a large jockey wheel?
jb
Posts: 1782
Joined: 6 Jan 2007, 12:17pm
Location: Clitheroe

Re: Had an accident - chain legnth

Post by jb »

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.
Cheers
J Bro
alexnharvey
Posts: 1923
Joined: 10 Jan 2014, 8:39am

Re: Had an accident - chain legnth

Post by alexnharvey »

fastpedaller wrote: 18 Apr 2021, 6:29pm But do these methods take account of long cage mechs, or mechs with a large jockey wheel?
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.

It would be easy to try it with four links first and see.
iandusud
Posts: 1577
Joined: 26 Mar 2018, 1:35pm

Re: Had an accident - chain legnth

Post by iandusud »

foxyrider wrote: 18 Apr 2021, 3:31pm
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.
+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.
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.

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.
gregoryoftours
Posts: 2234
Joined: 22 May 2011, 7:14pm

Re: Had an accident - chain length

Post by gregoryoftours »

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!
User avatar
Mick F
Spambuster
Posts: 56359
Joined: 7 Jan 2007, 11:24am
Location: Tamar Valley, Cornwall

Re: Had an accident - chain legnth

Post by Mick F »

cycleruk wrote: 18 Apr 2021, 4:07pm Big to Big + a link. Guarantees that the chain won't jam up if you select big ring to big sprocket.
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. :shock:
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!
Exactly!
Mick F. Cornwall
Pebble
Posts: 1934
Joined: 7 Jun 2020, 11:59pm

Re: Had an accident - chain length

Post by Pebble »

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
jb
Posts: 1782
Joined: 6 Jan 2007, 12:17pm
Location: Clitheroe

Re: Had an accident - chain length

Post by jb »

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.
Cheers
J Bro
Post Reply