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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 03-30-09, 08:50 AM   #1
fastenerpuller
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Bottom bracket, chainline- the chicken or the egg?

Hey everyone.

I am building up a bike, and I decided to use a sweet square taper dura-ace crankset I've been carrying around for years. I had the LBS remove the bottom bracket, which was a little more modern(I don't have the tools). I'd like them to put in a new BB so I can fool around with different chainring/sprocket combinations, but they insist that they need all of the parts so they can fool around with the chainline, before they'll know what bottom bracket to get.

I get the impression that they want to build up the bike for me, but I just want them to do the BB so it can be my bike. I can tell that I'll want the chainring as close to the BB as possible, but I also have a sweet, huge chainring I'd like to use if it clears. It's a dicey issue. What should I do?

In the interest of full disclosure, this bike has a 3 speed hub. (don't worry, I ride fixed too! Plus, this bike might end up as a singlespeed) I just thought that this forum would be the best to ask chainline quesitons.
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Old 03-30-09, 09:04 AM   #2
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Buy the tools, DIY :tup:
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Old 03-30-09, 09:37 AM   #3
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Determine chainline of rear hub first. Then, the bottom bracket width is chosen to align your specific crankset to the desired chainline.
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Old 03-30-09, 10:30 AM   #4
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Originally Posted by fastenerpuller View Post
Hey everyone.

I am building up a bike, and I decided to use a sweet square taper dura-ace crankset I've been carrying around for years. I had the LBS remove the bottom bracket, which was a little more modern(I don't have the tools). I'd like them to put in a new BB so I can fool around with different chainring/sprocket combinations, but they insist that they need all of the parts so they can fool around with the chainline, before they'll know what bottom bracket to get.

I get the impression that they want to build up the bike for me, but I just want them to do the BB so it can be my bike. I can tell that I'll want the chainring as close to the BB as possible, but I also have a sweet, huge chainring I'd like to use if it clears. It's a dicey issue. What should I do?

In the interest of full disclosure, this bike has a 3 speed hub. (don't worry, I ride fixed too! Plus, this bike might end up as a singlespeed) I just thought that this forum would be the best to ask chainline quesitons.
Contact Shimano, or an LBS that knows what they're doing and ask them what size spindle length you need for your BB. Is it a converted road crank, or a DA track crank?
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Old 04-06-09, 09:04 AM   #5
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Road crank. See, the thing is that there is no bottom bracket. So am I to understand that the "spindle length" is the important variable that will determine the position of the chainring and that the BB size is dependent only on the frame's BB shell dimension?

?????????
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Old 04-06-09, 09:14 AM   #6
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Ok, then there's this gobledy gook from the SA website concerning the dimension of my hub:

I've currently got a the dished 18t sprocket that comes with the thing, but the sprockets are very cheap and I will probably go with a smaller one unless I can fit the 52t chainring. I guess I'll measure it when I get home- from work!

• Chain Line: 1/8” Flat 13T ? 19T - 44.6 43.0
• Chain Line: 1/8” Dished 17T ? 22T - 46.3 44.7 42.9 41.3
• Chain Line: 3/32” Flat 16T - 44.8 44.2 43.2 42.6
• Chain Line: 3/32” Dished 17T ? 22T - 46.6 45.0 42.4 40.8
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Old 04-06-09, 09:49 AM   #7
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I just moved a crankset from one bike to another. I have the tools but didn't know what length spindle would work until it was installed and checked the clearance with the chain ring and chain stay.
I got a 110mm UN 54 and it was too short.
No problem..When I bought it I just asked the store, (with whom I have a relationship) if it's too short can I exchange it? Of course, so I took it back and got a 113mm and it's just right.

Buy the tools, you won't regret it. I have used the crank puller and BB tool many, many times.
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Old 04-06-09, 10:24 AM   #8
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Don't worry so much about your hub. Yes, it's important, but each crankset has a different BB spindle length requirement. You can always space out the cog if you need to move it to get your chainline just right. The BB cup size is different than the spindle length. The cup size is either going to be a 68mm or 73mm. I will wager that it's a 68 though, as you said it was a DA crankset. Which model DA is it. I'll see if I can hunt down the proper spindle length for you to get this resolved. My guess is that it's going to be either 110mm or 113mm. Probably the 113mm because of the 3spd hub.
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