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Discussion Starter · #1 · (Edited)
Let me preface this by saying that I KNOW YOU SHOULD NOT CROSS CHAIN, but I have SRAM RED and a 'sweet spot' for me for a lot of climbs around where I live is big ring large cog. Now I used to run this all the time with no problem, but now the chain seems to want to drop from the big ring completely OFF (not just down to the small chainring). I assume that this is being caused by the rear dr being too far in when in this combo causing the angle between the front and back to be too great - when I say too far in I mean the barrell adjuster could be adjusted to slightly move the bottom pulley out. Now before people start going off about cross chaining, SRAM even says one of the advantages of RED is being able to run big big with no rub..I have no rub with front dr in this combination, but almost tore up my rear dr this morning on a climb when the chain dropped off the front rings. Thoughts???? BTW, this is on a 61cm Cervelo RS (larger size would seem to have less of a problem due to longer chainstays REDUCING angle between chain rings and cassette).
 

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I don't think it would have anything to do with the derailleur - the issue is the chainline from the top of the cassette (the point where the chain last makes contact with the big cog as it moves clockwise) to the big chainring - adjusting the derailleur will have no effect on this.
 

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Give us a little more info. Is this std. or compact and how many miles on the drive train.
 

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Discussion Starter · #4 ·
Sram Red....

jd3 said:
Give us a little more info. Is this std. or compact and how many miles on the drive train.

Compact SRAM RED crankset and SRAM red cassette 11-23. About 2100 miles on the drivetrain. Oh yeah..one other thing....if I have it in the big ring and big cog or 2nd from the big cog and back pedal, sometimes the chain actually drops down into a smaller cog...weird, huh??
 

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It's usually the chainline.
On one of my bikes, if I go big-big, I'll drop the chain every time.
On my main race bike, I can ride big-big all day, with zero noise, and zero chance of dropping the chain.
 

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thoughts...

Using the big/big on a climb is just stupid. Shift to the little ring and 2-3 cogs smaller for the same rastio. I laugh when I see some dummy climbing a Colorado mountain in the big/big becaue he's doing "big ring intervals". The FD chain rub is trivial compared to the wear you're putting on the chain. I'd check the RD alignment and quite using the big/big. It's stupid.
 

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Discussion Starter · #7 ·
Yeah...

MR_GRUMPY said:
It's usually the chainline.
On one of my bikes, if I go big-big, I'll drop the chain every time.
On my main race bike, I can ride big-big all day, with zero noise, and zero chance of dropping the chain.
I used to be able to do it all day. I did it quite a bit today, then boom, chain dropped and rear dr almost got screwed...chain was coiled around the bottom pulley! Maybe it's just a dirty drivetrain. Hmm, what a novel idea!!! Anyone else with some ideas??
 

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I asked for details because I just went through a somewhat similar problem. My details, Sram compact Rival, approx 2000 miles, while riding in the big chainring / small cog, the chain would drop to the outside. It took me, my LBS owner and his best wrench to get it fixed. The problem started with a rattling noise at about 1800 miles. This started just a winter set in and riding was less frequent so it took about 100 miles to find the source and fix it. The lock ring on the cassette was lose and that was the noise. During this 100 miles was when the chain drop problem started. I thought when I found the lose cassette that the noise and the chain dropping would stop. Noise stopped, chain still dropped. New chain, chain still dropped. We began to look at the big chainring and replaced it. It was worn pretty good. Got the new one on but chain still dropped. Many front dr adjustments and chain still dropped. Finally after replacing all this and taking apart and cleaning the cassette, the problem is fixed. I'm still not sure exactly what fix it. I think that the Sram compact chain rings really take a lot of abuse. Running small / small the chain rubs on the big chainring and causes it to wear out fast. You're about the same millage I was. Inspect your big chainring. It may need replacing.
 
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