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I posted this in the niner sub-forum but thought the real SS experts would be here so...

At the risk of sounding like an idiot...

I have an '08 Air 9 that I want to run SS on. So I did my research and found that everyone is running the 32/20 "magic gear". I have a truvativ 32t ring on the front and 20t from an old cassette on the back. I have a brand new SRAM 8 speed chain with 47 links plus the quick link (47 outer plates). There is definitely too much slack with this combination.

However, if I put on my old 9 speed chain with 46 outer plates plus the quick link that is stretched, the chain is way too tight and I can't even get the wheel in the drops.

Did niner change the geometry from 08 to 09? Is it possible that my chain stays are longer or shorter than the current models?

Any help is greatly appreciated!
 

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wrxg33k said:
I posted this in the niner sub-forum but thought the real SS experts would be here so...

At the risk of sounding like an idiot...

I have an '08 Air 9 that I want to run SS on. So I did my research and found that everyone is running the 32/20 "magic gear". I have a truvativ 32t ring on the front and 20t from an old cassette on the back. I have a brand new SRAM 8 speed chain with 47 links plus the quick link (47 outer plates). There is definitely too much slack with this combination.

However, if I put on my old 9 speed chain with 46 outer plates plus the quick link that is stretched, the chain is way too tight and I can't even get the wheel in the drops.

Did niner change the geometry from 08 to 09? Is it possible that my chain stays are longer or shorter than the current models?

Any help is greatly appreciated!
Chain length is critical for magic gearing. I'm not talking link or half-link but fractions of an inch. A chain that is too long by 1/10" will dip in the middle by 1 inch (if you press on it with your finger). This fact makes magic gearing unacceptable for me, chains wear out too fast.

You can't expect a one-link or even a half-link change to hit the magic gear. The odds are against it.
 

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32:20 provided excellent wear life for me on a GT Zaskar. The chain was extremely tight initially, so I used 32:19 with a tensioner for a couple of rides, then switched the cog. Might be too much of a PITA for some, but worked well.
 

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thesergeant said:
32:20 is the magic ratio BUT you have to use SRAM's PC-1 chain. A 8 or 9 speed chain just has too much slack. How do I know? I'm the one that threw the photos up and posted about it a year ago maybe. Took a little experimenting but the PC-1 chain was key.
This makes no sense. How can the chain make it work or not? All chains with 47 links are the same length. Chain stretch can obviously make a big difference, but the kind of chain can't. If a new chain is too loose, and a worn chain with an extra link is too tight, you have 2 choices: Try a different gear combination, or use a tensioner.

Mark

PS: I recommend not to use the PC1 chain. It stretches very quickly and was noisy, even when clean and well lubed.
 

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I didn't take a caliper to the rollers and chain links but there has to be some kind of difference, regardless of how small. How else can you account for the difference in tension between the SRAM 8 and 9 speed chains (which I also experienced) and the PC-1. My tension with the PC-1 was perfect. No issues with chainwear either.

The photos above are teh proof. They were't photoshopped, I swear. :) Give it a try for yourself and report back the results.
 

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thesergeant said:
I didn't take a caliper to the rollers and chain links but there has to be some kind of difference, regardless of how small. How else can you account for the difference in tension between the SRAM 8 and 9 speed chains (which I also experienced) and the PC-1. My tension with the PC-1 was perfect. No issues with chainwear either.

The photos above are teh proof. They were't photoshopped, I swear. :) Give it a try for yourself and report back the results.
I'm not sure how to explain it. ANY new 1" pitch chain will be the same length when new, be it 8 speed, 9 speed, 10 speed, or singlespeed. They will certainly stretch at different rates. So you tried brand new versions of each of those chains and they had different tensions? That would be wierd.

Mark
 

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bikeny said:
I'm not sure how to explain it. ANY new 1" pitch chain will be the same length when new,
Mark
Nominally the same length (and bicycle chains are 1/2" pitch), but engineering tolerances come into play here, and even as little as a .0005" difference per link from one make of chain to another would affect chain length by .050" over 100 links.

This difference could come from bush/pin tolerances or the tolerances of the side plate length (how much under/over the nominal 1/2" it is.

And a difference of 0.50" is enough to prevent the chain fitting (or fitting but being too tight) and being too slack.
 

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thesergeant said:
I didn't take a caliper to the rollers and chain links but there has to be some kind of difference, regardless of how small. How else can you account for the difference in tension between the SRAM 8 and 9 speed chains (which I also experienced) and the PC-1. My tension with the PC-1 was perfect. No issues with chainwear either.

The photos above are teh proof. They were't photoshopped, I swear. :) Give it a try for yourself and report back the results.
Show me a new 8 speed chain on your bike. :)
 
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