Sizing the correct Bottom Bracket Trek 5200
11-08-16, 09:53 AM
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Sizing the correct Bottom Bracket Trek 5200
I am looking to replace the crank and bottom bracket on my Trek 5200 road bike.(2004) Nashbar has a compact double road crank that requires an Isis bottom bracket. The Octalink presently on the bike is 109.5 mm. The Isis Cranks on the Nashbar site are 108, 113. Will the 108 work on the Trek? Thanks in advance for any assistance.
11-08-16, 11:22 AM
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The length of the current bottom bracket is correct for the former crank but means nothing for the new one. You will have to find out what the new crank requires. Ask Nashbar what it needs.
11-08-16, 01:28 PM
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The 108/113 is probably for bikes that have a 130/135 OLD. Pick the correct size for the rear width.
11-08-16, 01:42 PM
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Think of your bottom bracket as an adapter that connects your crank to your frame. So obviously it has to match each of them.
1. The big majority of frames are machined for English threaded bottom brackets. There are some other designs but I'm pretty sure that your frame isn't one of those. English bottom brackets come in 2 widths 68 mm and 72 mm. Carefully measure your bottom bracket shell to know for sure which one you need.
2. Now to match the crankset. You already know you need an Isis BB to match the hole in your Isis crank. The crank also determines (mostly) the spindle length that you need. Don't guess. Check with Nashbar, they'll know which length that you need. Sometimes the recommended length is listed as something like 108/113. If that's the case, measure the distance between your rear dropouts. It'll probably be 130 mm or 135 mm. If it's 130, pick 108. If it's 135, pick 113. That way your chain will line up better with your cassette.
1. The big majority of frames are machined for English threaded bottom brackets. There are some other designs but I'm pretty sure that your frame isn't one of those. English bottom brackets come in 2 widths 68 mm and 72 mm. Carefully measure your bottom bracket shell to know for sure which one you need.
2. Now to match the crankset. You already know you need an Isis BB to match the hole in your Isis crank. The crank also determines (mostly) the spindle length that you need. Don't guess. Check with Nashbar, they'll know which length that you need. Sometimes the recommended length is listed as something like 108/113. If that's the case, measure the distance between your rear dropouts. It'll probably be 130 mm or 135 mm. If it's 130, pick 108. If it's 135, pick 113. That way your chain will line up better with your cassette.
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11-08-16, 02:32 PM
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thanks
Thanks for the advice. Should make things fairly straight forward.
