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Old 07-12-12, 11:17 AM   #1
mwilden
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What size bottom bracket??

I recently bought a used 1999 Trek 2000t. Drivetrain is completely shot on it. I got a great deal on a new HG chain and a Shimano CS-HG50 13-26t 8 speed cassette, which is same exact configuration as stock. Front chain rings need replaced on it also but its looking like it will just be cheaper to replace whole crankset. Bike currently runs 30/42/52t chainrings with 175mm square taper RSX cranks. The Shimano 2303 crankset has same exact configurations. My question is this... My current bottom bracket is 68x118, will that work with the 2303 crankset or should I replace BB with a shorter spindle? If so any recommendations on which model BB I should go with? Thanks for your input!!!
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Old 07-12-12, 12:29 PM   #2
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I recently bought a used 1999 Trek 2000t. Drivetrain is completely shot on it. I got a great deal on a new HG chain and a Shimano CS-HG50 13-26t 8 speed cassette, which is same exact configuration as stock. Front chain rings need replaced on it also but its looking like it will just be cheaper to replace whole crankset. Bike currently runs 30/42/52t chainrings with 175mm square taper RSX cranks. The Shimano 2303 crankset has same exact configurations. My question is this... My current bottom bracket is 68x118, will that work with the 2303 crankset or should I replace BB with a shorter spindle? If so any recommendations on which model BB I should go with? Thanks for your input!!!
Most crankset specs. list a suggested spindle length, so you could try checking there. Or id the current BB is still in the frame, mount the crank, measure the chainline (distance from the center between inner and outer rings to center of frame, or from center of chainrings (eyeball is close enough) to side of a frame tube + half the diameter) and see if you need to move it in, and by how much.
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Old 07-12-12, 02:06 PM   #3
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Most crankset specs. list a suggested spindle length, so you could try checking there. Or id the current BB is still in the frame, mount the crank, measure the chainline (distance from the center between inner and outer rings to center of frame, or from center of chainrings (eyeball is close enough) to side of a frame tube + half the diameter) and see if you need to move it in, and by how much.
Great info, thank you. This may be a dumb question but what is the chainline supposed to be?
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Old 07-12-12, 02:47 PM   #4
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Great info, thank you. This may be a dumb question but what is the chainline supposed to be?
I hate remembering every spec. so I always measure and confirm. Measure from the middle of the cassette, out to the inside of the dropout and subtract that from half the dropout width.

But you can always look it up here (scroll most of the way to the bottom for the centerline info)
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Old 07-12-12, 04:16 PM   #5
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IIRC, Shimano recommends a 113mm spindle with 2203/2203 cranks for a 45mm chainline.
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Old 07-12-12, 09:22 PM   #6
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mwilden, It's best to try the new crankset on the old BB. Specs can sometimes change with oversize seat tubes. You want the middle chainring to align between the 4th and 5th rear gear, but this isn't an absolute requirement. An oversized seat tube effects the swing, or arc of the FD sometimes requiring a slightly longer BB spindle.

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