measuring new chain

snig

what's the best way to measure a new chain?

I can't use the old one as it will be a different size.

I've watched 5 Youtube videos and each one showed a different way to do it, from large chainring to smallest cassette ring, to largest/largest, and even largest and 2nd largest cassette ring and not threading through the jocky wheel and adding 2 links, I guess they will work but is one method more reliable than the others?

Underscore

snig wrote:

what's the best way to measure a new chain?

With a tape measure!

snig wrote:

I've watched 5 Youtube videos and each one showed a different way to do it, from large chainring to smallest cassette ring, to largest/largest, and even largest and 2nd largest cassette ring and not threading through the jocky wheel and adding 2 links, I guess they will work but is one method more reliable than the others?

As far as I'm aware (and this is what I've always done), find the point that would allow it to just go round the largest chain-ring and largest sprocket (ignore the derailleur) and add one full link (i.e. two half-links). That's always worked for me when I've not had an existing chain to measure against.

HTH,

_

The Rookie

That is the correct process, and while a slightly different description gives the same result as using the guide that comes with Shimano and also SRAM chains.

Parktools recommend that method and fully describe it on their website.

snig

Underscore wrote:

snig wrote:

what's the best way to measure a new chain?

With a tape measure!

snig wrote:

I've watched 5 Youtube videos and each one showed a different way to do it, from large chainring to smallest cassette ring, to largest/largest, and even largest and 2nd largest cassette ring and not threading through the jocky wheel and adding 2 links, I guess they will work but is one method more reliable than the others?

As far as I'm aware (and this is what I've always done), find the point that would allow it to just go round the largest chain-ring and largest sprocket (ignore the derailleur) and add one full link (i.e. two half-links). That's always worked for me when I've not had an existing chain to measure against.

HTH,

_

Just read Park tools advice and they say add 2 links, which is a distance of one inch.

drlodge

Fit it on small-small and adjust to the longest length you can with some tension in the rear derailleur.

anthdci

drlodge wrote:

Fit it on small-small and adjust to the longest length you can with some tension in the rear derailleur.

this is how i do it, as long as possible without the chain rubbing on itself

drlodge

anthdci wrote:

drlodge wrote:

Fit it on small-small and adjust to the longest length you can with some tension in the rear derailleur.

this is how i do it, as long as possible without the chain rubbing on itself

Exactly. That way the chain is as long as possible, and can't be too short.

snig

drlodge wrote:

anthdci wrote:

drlodge wrote:

Fit it on small-small and adjust to the longest length you can with some tension in the rear derailleur.

this is how i do it, as long as possible without the chain rubbing on itself

Exactly. That way the chain is as long as possible, and can't be too short.

but wouldn't pulling the derailleur too tight leave you with a chain too short?

you would have to know what position the derailleur should be in at it's tightest point.

Think the large/large without the derailleur playing a part is the method for me.

drlodge

snig wrote:

but wouldn't pulling the derailleur too tight leave you with a chain too short?

you would have to know what position the derailleur should be in at it's tightest point.

Think the large/large without the derailleur playing a part is the method for me.

Using my method, the derailleur can only be too tight if the derailleur doesn't have sufficient capacity. And that has nothing to do with the length of the chain.

anthdci

snig wrote:

but wouldn't pulling the derailleur too tight leave you with a chain too short?

what do you mean?
The derailleur isn't not too tight, if anything it is near it's most natural state without the pressure from the chain.

edit: this guide describes how I do my chain
http://www.slowtwitch.com/Tech/Chain_How-To_-_Part_1_3279.html

mr_evil

The small-small method is best, as then you can change to a larger cassette and the chain will still be long enough.

snig

anthdci wrote:

snig wrote:

but wouldn't pulling the derailleur too tight leave you with a chain too short?

what do you mean?
The derailleur isn't not too tight, if anything it is near it's most natural state without the pressure from the chain.

yeah confusing myself was thinking large/large, then you would have to be careful not to pull the derailleur too tight if you were using the derailleur, just adding 2 links would be the safest bet.

Just tried the small/small and it probably is the better option after all as as you say, the derailleur is at it's max extension and can not be moved past that point, not the case if using the large/large method (I think)

The Rookie

Small small, what a load of tosh, but then clearly you know more about getting the chain length right than Shimano, SRAM, and KMC or Parktools......

That and spend a fortune on a lighter bike and carry more weight.....

I'll stick to the right method which is big/big and at least one pair of links overlap.

drlodge

The Rookie wrote:

Small small, what a load of tosh, but then clearly you know more about getting the chain length right than Shimano, SRAM, and KMC or Parktools......

That and spend a fortune on a lighter bike and carry more weight.....

I'll stick to the right method which is big/big and at least one pair of links overlap.

Other than saying "I'm wrong" you provide no explanation or argument. The "big/big and at least one pair of links overlap" method is based on certain assumptions which may not hold true and therefore does not guanantee the correct length, unlike my method which is certain to give you the correct length chain i.e. one that is neither too long nor too short.

"at least one pair of links overlap" - so do you mean one link, 2 links, 3 links, how many exactly? On my bike there is only one correct chain length since I am at the capacity of my rear derailleur (34-50 and 12-29) and your method is too error prone.

No idea what you are going on about with the weight bit, its clearly irrelevant to the topic. The Rookie indeed.

The Rookie

The right method guarantees it's not to short, as it provides the right length for the 'longest case', it also guarantees it's not to long unless you have the wrong mech, in the same way your small small can't guarantee it's long enough if the rear mech is wrong (capacity), having said that being too short is the more dangerous as it pulls the mech into the cassette, so I'll stick to the one hat guarantees it's not to short rather than hoping it's all specced right so may not be too short.

I would have thought it rather pursuasive that the worlds two largest drivetrain suppliers (chains, mechs, chainwheels and cassettes) use a method that although worded slightly differently gives the same length as the one I'm suggesting.

drlodge

Actually I think we are both right - both methods are doing the same thing, but from different perspectices (small-small vs big-big). Therefore as long as the rear derailleur is of sufficient capacity, both methods will work just fine. Which ever method is used I would always suggest double checking the chain in both small-small and big-big to ensure both extremities are ok. Manufacturers will suggest the big-big method to safeguard against numpties using rear derailleurs of insufficient capacity since, as you say, you really don't want to have a chain that's too short.

I guess the reason why I prefer my method is that is gives a chain length as long as possible and therefore no need to worry if you change the rear cassette for one with a lower bottom gear (e.g. changing from 12-25 to 12-28). Using small-small, the chain is already the "right" length, but using big-big it'll be too short and you'll need a new chain (or insert some links that you previously removed, if you still have them).

I recently changed from 12-27 to 12-29 and had I used big-big to size the chain, I would likely have needed a new one.

The Rookie

drlodge wrote:

I guess the reason why I prefer my method is that is gives a chain length as long as possible and therefore no need to worry if you change the rear cassette for one with a lower bottom gear.

Alternatively, I prefer it as short as possible as it weighs less (and the weight loss is free - in fact it gives me longer spare sections for possible repairs), also the rear mech gives better chain control ( - through it's operating angle and controlling less weight) though less applicable on my commuter (only 2 bunny hops each way) than on my MTB's (lots of clattering around).

Having once had the rear mech go into the cassette on a borrowed bike, I'd never want to repeat that, although as long as the 'small - small' is double checked on big big, I guess that is no less likely to happen.

mr_evil

The Rookie wrote:

...The right method guarantees it's not to short, as it provides the right length for the 'longest case', it also guarantees it's not to long unless you have the wrong mech, in the same way your small small can't guarantee it's long enough if the rear mech is wrong (capacity), having said that being too short is the more dangerous as it pulls the mech into the cassette, so I'll stick to the one hat guarantees it's not to short rather than hoping it's all specced right so may not be too short....

If you size the chain big-big, then swap cassettes, you can then end up with a chain that is too short. That's much more likely than someone starging off with a mech with insufficient capacity. Small-small ensures that the chain will be long enough in this case.

The Rookie wrote:

...I would have thought it rather pursuasive that the worlds two largest drivetrain suppliers (chains, mechs, chainwheels and cassettes) use a method that although worded slightly differently gives the same length as the one I'm suggesting.

They obviously don't expect end users to swap cassettes, or don't care if doing so will require that they purchase a new chain.

The Rookie wrote:

...in fact it gives me longer spare sections for possible repairs...

You should not repair chains like that. Unless it is still new, the spare links will be shorter than the ones already there.

t4tomo

Mr Evil wrote:

The Rookie wrote:

...in fact it gives me longer spare sections for possible repairs...

You should not repair chains like that. Unless it is still new, the spare links will be shorter than the ones already there.

Indeed, your better off with a slightly longer chain on the bike, then if it snaps whilst you are out you can repair with a quick link (which often necessitates sheding a half link or two) and not leave tyour chain too short.

The Rookie

Well this is the first time on this forum anyone has suggested anything but big big, why carry more weight and lose chain control when you don't have to.

If you fit a bigger cassette, fit a new chain or lengthen it!

Personally I think it's stupidity to have it any longer than needed, no good reason and lots of bad ones, so I'll stick to what the experts (as above) say is right thanks.

bianchibob

Try this link....has always worked for me.

http://www.epicidiot.com/sports/chain_l ... ulator.htm

supersonic

The derailers are not always of sufficient capacity - the 'big-big' method means you have no chance of causing damage should you go into this combo. I have seen frames bent from chains too short, and I see far too many derailers of insufficient capacity. Even on new bikes!

drlodge

tenratdep5 wrote:

The small-small method is best, as then you can change to a larger cassette and the chain will still be long enough

Indeed, my preferred method as this puts the chain as long as possible. I understand where the "big-big" guys are coming from but in the end, a derailleur of insufficient capacity is going to cause issues which ever way you choose, you should *always* double check big-big and small-small after fitting.

Its not an issue with my bike, since there is only 1 length that is the right one and is going to work!

The Rookie

Yes but use big-big and it just goes slack if the mech doesn't have the capacity, get the chain too short and major damage to bike and rider can ensue......fail safe would be big big