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Chain line question

Old 12-09-10, 09:22 AM
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Fizzaly
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Chain line question

Im just wanting to make sure i have this understood correctly, to measure if im running the correct length Spindle i measure from the center of the seat tube to the middle chain ring (im running triple) and want to get that number as close to 50mm as possible?
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Old 12-09-10, 09:48 AM
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Fizzaly, Yes. My triple measures ~51 mm using the bottle bracket rivlets as a centerline.

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Old 12-09-10, 11:20 AM
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Per Sheldon:

47.5-50mm for a mountain triple.

45mm for a road triple.

43.5mm for a road double.

Seat tube centerline to chainring centerline.

Given it's within a couple of mm, I don't worry much about it. I can always seem to get it working pretty well.
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Old 12-09-10, 11:30 AM
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More generally, the centerline of the chainrings should be as close as possible to the centerline of the cassette or single sprocket.

You can find the rear centerline distance by measuring the distance from the inside of the right dropout to the center of the cassette or sprocket, and subtracting that from the half of rear axle's width.

If you prefer not to take a few measurements and do some arithmetic, you can refer to charts for various types of bikes, as given by Sheldon Brown.
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Old 12-09-10, 11:43 AM
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Do I understand this correctly--chainline is mainly to insure most efficient power transfer? In other words, having both the cassette center cog and middle ring 48mm from the bikes center line (for example) will cause the least amount of 'cross chaining', thus be most efficient?

I have tried to make my setups match f/r for chainline, but in a couple cases, had to move the crank outward to avoid the small ring contacting the chainstay. I use whatever crank (MTB or road) will hold the rings I want to use, so they are not always 'ideal'. I am more concerned with function than fashion, so if it works, I am satisfied.
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Old 12-09-10, 11:46 AM
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Thanks just wanted to make sure i read it right
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Old 12-09-10, 11:49 AM
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Originally Posted by badamsjr View Post
Do I understand this correctly--chainline is mainly to insure most efficient power transfer? In other words, having both the cassette center cog and middle ring 48mm from the bikes center line (for example) will cause the least amount of 'cross chaining', thus be most efficient?

I have tried to make my setups match f/r for chainline, but in a couple cases, had to move the crank outward to avoid the small ring contacting the chainstay. I use whatever crank (MTB or road) will hold the rings I want to use, so they are not always 'ideal'. I am more concerned with function than fashion, so if it works, I am satisfied.
My problem is my most used gears no matter which "set" i use i get some pretty bad cross chaining and have been breaking chains. It doesn't help that i have a frankenstein bike either with a diverse mixture of road and mtb parts
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Old 12-09-10, 12:07 PM
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Originally Posted by badamsjr View Post
mainly to insure most efficient power transfer?
More to minimize wear and maximize shifting performance.

Today's more flexible chains provide similar efficiency regardless of chainline (within reason.)

I think I could make a road triple FD work with a 47.5mm chainline. I sincerely wonder if I could get it to swing wide enough to reliably and predictably shift a 50mm chainline.

Same thing goes in reverse. I sincerely wonder if I could get a mountain FD swing far enough inside to shift a 43mm chainline.

Both scenarios lie well outside the ±2-ish mm range I aim for.
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Old 12-09-10, 01:08 PM
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Originally Posted by Fizzaly View Post
My problem is my most used gears no matter which "set" i use i get some pretty bad cross chaining and have been breaking chains. It doesn't help that i have a frankenstein bike either with a diverse mixture of road and mtb parts
I hear you. I am a firm believer in "mix-n-match", but I try to keep things working as efficiently as I can, no matter what brand/type components I use.

On chains, I have found SRAM 990 Hollow pin MTB chains work very well in all my 9spd applications. Fairly light, and as strong as I could ask for.
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