Bicycle Mechanics - Bottom Bracket
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According to Sheldon Brown, a Phil Woods bottom bracket with,
68 mm Cartridges will have approximately 2.5 mm of the rings extending from both sides of a 68 mm shell. The 68 mm cartridge in a 73 mm shell will allow the rings to be flush with the shell.This crankset,
asks for a 103mm bottom bracket for a 42mm chainline (assuming a 68mm shell).
My question is, since I have a 73mm bottom bracket shell width do I need to account for this in the spindle length? Should I therefore get a 108mm spindle to compensate for the 5mm lost on the shell width? Thanks.
02-12-09, 11:01 PM
Im not a bicycle mechanic and I am currently undergoing a Bottom bracket issue myself. Apparently the forum is a bit shy of people that can match a particular crank with a particular bike with a particular Bottom Bracket. The advice that I have gotten from two separate mechanics at my LBS is that you really need to conduct a trial and error process once you've found the cranks you want because you also have to consider the amount of arch in the crank arms. I know this didnt help much but I didnt want you to think that you got left hanging. Its not a good feeling especially with a complicated issue like this that someone should standardize.
02-13-09, 12:13 AM
The 42mm chain line fighure is the measurement from the center of the bb shell (centerline of frame) to the middle of the chainring, usually measured from the center of the seat tube to the center of the ring.
Now, if you were to use a phil bb with a 103mm spindle in either a 68 or 73 mm shell the chain line should be the same. as sheldon states, the cups on a 68 shell will stick out about 2.5 mm on each side. that adds up to 5mm, the exact diffefence between a 68 and 73. This means that when you install the phil 103 bb in your 73 mm shell the cups will be flush with the frame, not sticking out as they would in a 68mm bb shell. As long as you use a phil 103 mm bb axel you will be fine.
Keep in mind that you can adjust the chain line with phil wood bottom brackets to fine tune your chain line.
The reason this will work with the phill bb is because of the fact that the phil wood bb does not use a fixed cup like most other bottom brackets. if you were to use a standard cratridge bottom bracket then you would probabbly run into some problems due to the spindle being offset to one side.
disclaimer: i just got back from drinking at my friends house so this makes sense in my head. apologizes if my explanation is completely whack.
I am not sure if I am making this harder than is should be or I just don't understand but, it is my understanding that the crankset asks for a 103mm bottom bracket assuming a 68mm shell width. If I were to use these cranks with a 73mm shell width do I need to compensate with a 5mm longer spindle since the spindle wont be extending as far beyond the shell with a 73mm width?
02-13-09, 11:00 AM
I think what the previous post was trying to say was that the long bottom bracket shell will be used with a bottom bracket cartridge that has caps that will actually fit mostly within the bottom bracket shell. The 68 mm bottom bracket shell has caps that actually protrude out and make your bottom bracket shell essentially longer by 5mm which makes the total exposed spindle length the same for either application.
oh, duh. Definitely a case of over thinking or just plain stupidity on my part. Thanks Calvin.
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