misaligned chainline ?
11-07-09, 07:25 AM
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misaligned chainline ?
I just replaced my old 9 speed Ultegra 11-23 rear cassette with a new 12-27. I have a 9 speed Ultegra double crankset. My chain line seems to be screwed up. When in the smaller ring, my chain rubs against the inside wall of the larger ring when in the 8th cog or second to last high gear. I never use the small crank ring with the two smallest rear cogs but I never had rubbing even when I shifted into the highest cog for storage purposes. What can I do to adjust?
11-07-09, 02:11 PM
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If you never use that combo, the easiest route would be, continue not using it. 
Wider bottom bracket maybe?
Wider bottom bracket maybe?
11-07-09, 06:40 PM
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I've seen this with several Ultegra 9-speed cranksets, don't know why but it's usually just the 9-speed Ultegra doubles.
Assuming you have a conventional bottom bracket, not the newer outboard bearing type, you can easily cure this chainline problem with a 1.5 or 2mm bottom bracket spacer. It's easy to install and you won't even have to break the chain. It goes between the BB cup and the frame. It will be hardly noticeable. I put one on my wife's bike.
You should be able to use the next to smallest cog without rub on the side of the big ring.
Al
Assuming you have a conventional bottom bracket, not the newer outboard bearing type, you can easily cure this chainline problem with a 1.5 or 2mm bottom bracket spacer. It's easy to install and you won't even have to break the chain. It goes between the BB cup and the frame. It will be hardly noticeable. I put one on my wife's bike.
You should be able to use the next to smallest cog without rub on the side of the big ring.
Al
11-08-09, 06:02 AM
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Shortly after writing the question I tightened the cables which did help a touch but I think a spacer for the bottom bracket makes a lot of sense. Thank you. It still seems strange that there would be a difference within the two cassettes.
11-08-09, 08:51 AM
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Before installing a spacer that is not needed, check the chainline. Nearly all double crank has the same chainline, but it's listed as 43.5mm to a point in space, between the rings that can't be measured. The easy way to measure the chainline is from the side of the seat tube to the tip of a tooth on the little ring. Measure that distance with a precision scale and then add half the seat tube diameter. The total should be very close to 40mm.
