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Chain Length

877 views 9 replies 4 participants last post by  guppie 
#1 ·
Question-Should I be able to measure the old chain to figure how long the new one will be?
I am switching from an 8 speed to a 9. The gears are almost the same (44 large-but 32 not 34 on the Cassette) In measuring the 44 ring I find the old is 6 7/8 and the new is 7 1/4 In. (3/8 difference??) Laying them on a bench for the old at 53" chain it is about one half a link longer, but this might be stretch. I know the directions say to run the chain over both large rings and add two or three links, but have not taken the old crank and cassette off yet. (waiting for a tool kit)
:madman:
 
#2 · (Edited)
I'm scratching my head over your chainring measurement. Your chain is not flexible, being constructed of 1/2" rigid links, so it sees a 44T chainring as 22" in diameter (no more, no less).

It sounds like you're anxious to get working on this project, but trust me, just leave the chain alone until you get the drivetrain parts all mounted up. Then, as you already referenced, use the tried 'n true big-big chain sizing method:



Don't use your old chain as a starting point. The 2T difference in your cassette may have no impact, but you may be surprised at how often stock chains are sized too long for the bikes they come with.
 
#4 ·
Thanks Nate. I was trying to figure if the fount dérailleur would mount to the same hight as the old. The 7 & 1/4" measurement was the diameter not the circumference. You answered my question about 8 virsa 9 speed chain length being 1/2" and the same. the diff. from my old chain has to be stretch. I do intend on waiting but was looking for problems and trying to get answers before the build. It is my first.
 
#5 ·
Fletch6 said:
Thanks Nate. I was trying to figure if the fount dérailleur would mount to the same hight as the old. The 7 & 1/4" measurement was the diameter not the circumference. You answered my question about 8 virsa 9 speed chain length being 1/2" and the same. the diff. from my old chain has to be stretch. I do intend on waiting but was looking for problems and trying to get answers before the build. It is my first.
That's still a puzzling difference. Are you measuring tip to tip? I'd bet you'll see a smaller difference if you measure valley to valley.
 
#6 ·
Yes valley to valley comes out to 6 1/2 on old and 6 3/4 on new. This is with a tape measure and could be 1/8 or so larger difference. I measured tip to tip because I figured it might be more worn in the valley and for me it was harder to measure.
 
#8 ·
Can I assume you measure chain length the same way (big-big) even if you run a bash guard instead of a big ring? So in my case I'd actually be measuring big-middle? (rr-fr)

I've never used my big ring on a trail as I always use the middle ring. I'm not doing any DH or FR crazy stuff, just typical weekend warrior trail riding (aggressive XC). Would losing my big chainring be a problem? Why don't more XC racers do this to shave weight (- big ring, - chain links)? Or maybe they do????
 
#9 ·
guppie said:
Can I assume you measure chain length the same way (big-big) even if you run a bash guard instead of a big ring? So in my case I'd actually be measuring big-middle? (rr-fr)
There's nothing "official" from SRAM and Shimano, but after playing around with a 1x9, and based on some previous posts, adding an extra pair of links to the big-big rule is a good idea.

The traditional big-big rule assumes you'll not be running the big-big combo, and is there to protect you if you accidentally shift there. But with a 2x9 or 1x9 setup, the whole range of the cassette is fair game from your new "big ring," and the extra links allow a slightly more relaxed forward cage extension.

Throw an extra Power Link in there and see what difference the two lengths make on your bike.
 
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