Which of these is the right method for setting chain length?
05-08-14, 03:23 PM
#51
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Thread Starter
Hey guys, I really appreciated your help in this thread. I sized the chain a couple weeks ago, everything came out great and I'm out enjoying.
Thanks again!
Thanks again!
05-08-14, 10:01 PM
#52
Keepin it Wheel
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I've said this so often it's like a Mantra.
There are 3 chain lengths.
1- the Minimum - found by the big/big +1" method (note: this is an absolute minimum method with no fudge room.
2- the Maximum - found by the small/small & take up slack method. This has some fudge room if wide range gearing exceeds RD take up capacity.
3- Correct length - anything between the minimum and maximum, according to RD cage orientation, or your preference.
I run chains near the maximum because it leaves me room to change to a larger cassette or remove damaged links if I ever need to. While some people run minimum length and carry spare links, my spares are already in the chain.
IMPORTANT -- the minimum is an absolute non-fudgeable length, so unless you're sure your gear combination is within RD capacity, measure the minimum and confirm that your length is longer. Or if confident, shift into big/big (slowly) after cutting to confirm.
BTW- if setting up a race bike always use the maximum method. The few grams of added weight are well worth it because it allows you to use a donated or neutral support wheel in a race without worry about the cassette size.
I once watched a rider with a corn cob cassette grab a donated wheel after flatting, and destroy his drivetrain at the first hill when he shifted to a sprocket too large and ran out of chain.
There are 3 chain lengths.
1- the Minimum - found by the big/big +1" method (note: this is an absolute minimum method with no fudge room.
2- the Maximum - found by the small/small & take up slack method. This has some fudge room if wide range gearing exceeds RD take up capacity.
3- Correct length - anything between the minimum and maximum, according to RD cage orientation, or your preference.
I run chains near the maximum because it leaves me room to change to a larger cassette or remove damaged links if I ever need to. While some people run minimum length and carry spare links, my spares are already in the chain.
IMPORTANT -- the minimum is an absolute non-fudgeable length, so unless you're sure your gear combination is within RD capacity, measure the minimum and confirm that your length is longer. Or if confident, shift into big/big (slowly) after cutting to confirm.
BTW- if setting up a race bike always use the maximum method. The few grams of added weight are well worth it because it allows you to use a donated or neutral support wheel in a race without worry about the cassette size.
I once watched a rider with a corn cob cassette grab a donated wheel after flatting, and destroy his drivetrain at the first hill when he shifted to a sprocket too large and ran out of chain.
I have a pretty wide range; 52/39 up front and 11-32 in back (or is it 11-34 even? I forget). I just put my KMC X9.93? .95? chain on whole, I think it is 114 links. My RD is a MTB long cage, so it can take up the slack, but it seems to me the chain is really loose/low tension, and I try to avoid small/small. If I get above the middle of the cassette in the small ring I prefer to shift up to the big ring just to take up slack. Otherwise, I get a lot of bouncing on the chainstay (so I got a neoprene/velcro chainstay protector -- it is FILTHY (with Chain-L))
So is that bad? Should I take out a few links so the small/small combination is not so floppy? (keeping enough for the big/big of course)
?
05-08-14, 10:03 PM
#53
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He knows even more about chain lube...
05-08-14, 10:45 PM
#54
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It wasn't funny at the time, and cost serious dough to fix.
...My RD is a MTB long cage, so it can take up the slack, but it seems to me the chain is really loose/low tension, and I try to avoid small/small. ..... Otherwise, I get a lot of bouncing on the chainstay ...
So is that bad? Should I take out a few links so the small/small combination is not so floppy? (keeping enough for the big/big of course)
Most RDs use idler cage springs with a number of turns. So the small change in spring wind up with different sprockets, or from using a longer or shorter chain doesn't change tension much. You can test this for yourself by pulling the lower loop forward and you'll find yourself pulling against a relatively constant spring force.
You do get changes based on the angle of the cage, because sometimes it's puling in line with the chain and sometimes almost perpendicular. So actually you might get the highest chain tension when the idler pulley is all the way back.
Large cage RDs generally result in lower chain tension because makers don' use a stronger spring to compensate for the longer arm, which needs higher spring torque to produce the same tension (kids of different weight who use seesaws understand this effect).
However the real cause of chain slap when riding small/small is much simpler. It's that the chain is riding that much lower, and closer to the stay, so it takes that much less movement to get slap. mtn bike makers know this, which is why some move the chainstay above the chain, or arc it lower.
...My RD is a MTB long cage, so it can take up the slack, but it seems to me the chain is really loose/low tension, and I try to avoid small/small. ..... Otherwise, I get a lot of bouncing on the chainstay ...
So is that bad? Should I take out a few links so the small/small combination is not so floppy? (keeping enough for the big/big of course)
You do get changes based on the angle of the cage, because sometimes it's puling in line with the chain and sometimes almost perpendicular. So actually you might get the highest chain tension when the idler pulley is all the way back.
Large cage RDs generally result in lower chain tension because makers don' use a stronger spring to compensate for the longer arm, which needs higher spring torque to produce the same tension (kids of different weight who use seesaws understand this effect).
However the real cause of chain slap when riding small/small is much simpler. It's that the chain is riding that much lower, and closer to the stay, so it takes that much less movement to get slap. mtn bike makers know this, which is why some move the chainstay above the chain, or arc it lower.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 05-08-14 at 10:54 PM.
05-09-14, 05:00 AM
#55
Senior Member
Thanks for the take on tension, that's what I enjoy about popping in here is learning things like that.
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