Ideal Chain Length

Raymzor

Is there a guide/ formula for working out ideal chain length? i have a 50/34 compact and an 11-25 cassette. when i run the 34-11 the chain is rubbing off the rear mech as if the chain is too long. any comments or advice?

Holyboy

Your chain is too long!!!

macnab

There is an adjuster on the derailleur that should move it away from the sprocket, have u tried that

Holyboy

Small ring/smallest sprocket and remove enough links so the chain is as close to the mech but not actually touching it, there are exceptions to this rule but not with your set up.

AltAccount

I'd tend to put it in the 50-25 and then make the chain as short as comfortably/reasonably possible - but not mental tight.

tomasrojo

This has worked for me:

SIMPLE EQUATION: L = 2 (C) + (F/4 + R/4 + 1)

L = Chain length in inches. Round the final result to closest whole inch figure.
C = Chain stay length in inches, measure to closest 1/8”. Use chart below to find decimal measurement.
F= Number of teeth on largest front chainring.
R= Number of teeth on largest rear cog.

http://www.parktool.com/blog/repair-help/chain-length-sizing

Mycroft H

Lumen will have a spreadsheet for it, guaranteed :-)

As short as you can get away with I'd imagine

deandean

Set the chain up on the largest front chainring and the largest rear sprocket.

Pull the chain tight until the derailleur is fully extended.

Add 1 link if needed.

That's your chain length.

P.S. AARGH DO NOT RUN THE 11-34! Avoid this ratio. Use your gears properly.

Lumen

53

rab!dmonkey

The instructions which come with SRAM chains recommend routing the chain around the largest chainring and the largest cog (not going through the rear derailleur), pulling it taught and adding one link to that length. Sheldon Brown concurs.

lescol

This works for me:- http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

It also agrees with Lumen...53 links

Hungrycol

tomasrojo wrote: »

This has worked for me:

http://www.parktool.com/blog/repair-help/chain-length-sizing

Lumen

The problem with over-optimising for one specific combination of gears is that you're stuffed if you want to stick a different combination on, e.g. a 28 sprocket for a hilly event or holiday.

This is fine if you have a re-joinable chain (e.g. Wipperman) - you could have a collection of 52, 53 and 54 link chains, but otherwise you're a bit stuffed.

Also, who uses 11-34 cassettes on road bikes?

ROK ON

Lumen wrote: »

Also, who uses 11-34 cassettes on road bikes?

David Millar

Captain Havoc

rab!dmonkey wrote: »

The instructions which come with SRAM chains recommend routing the chain around the largest chainring and the largest cog (not going through the rear derailleur), pulling it taught and adding one link to that length. Sheldon Brown concurs.

This is what I do.

Raymzor

Lumen wrote: »

The problem with over-optimising for one specific combination of gears is that you're stuffed if you want to stick a different combination on, e.g. a 28 sprocket for a hilly event or holiday.

This is fine if you have a re-joinable chain (e.g. Wipperman) - you could have a collection of 52, 53 and 54 link chains, but otherwise you're a bit stuffed.

Also, who uses 11-34 cassettes on road bikes?

Thanks Lumen. My cassette is an 11-25 and chain rings are 34-50. I do realise that in principal i should not cycle with the 11 rear, 34 front combo but in principal i think the chain should not be rubbing on the rear mech. time to count the links!

Raymzor

right lads and lasses, link count is 53. i recently changed cassette from 12-25 to 11-25 so this must lead to more chain slack in the bottom gear, therefore i intend shortening to 52 links. it may put extra pressure on the rear mech if i push 50/25 but i suppose this is not adviseable anyway:) it is worth noting that the formulae and guidelines dont account for running an 11 or a 12 as the lowest gear. i have also bought a chain wear tool check for wear but the chain is not too old!

Lumen

34-11 is also not advisable.

piston

Run the chain around the largest sprocket and largest chainwheel without putting it through the derailleurs and judge what length it should be then add one complete link.