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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 02-24-09, 02:25 AM   #1
maxbicyclemax
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Bottom bracket, crank exchangeablity??

What are some of the important measurements of bottom brackets, threads, width, brearing sizes etc.

So if i want to change my "mmm, sora" crankset on my giant, do i have to stick with Shimano??

i see on ebay brands like, Raceface, FSA, Sram etc what measurements need to match, (i know about crank length)

anyone know of a website with exploded views of the BB?
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Old 02-24-09, 09:55 AM   #2
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BB shell width/threading/spindle length are going to be your major concerns.

If it's a Giant, it's probably standard threading, you'll need to measure the spindle and BB shell to see what size you need.

You can use whatever BB meets your measurements, but Shimano pretty much nails the quality/price equation.
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Old 02-24-09, 11:23 AM   #3
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Bottom bracket type will be important. If you have cartridge BB, Is your BB spindle square taper (I'm thinking not because I am inferring a relatively new bike) or octalink (maybe, depending on how old crankls are). Or do you have external bearings with integrated spindle cranks (i.e. spindle is part of crankset not part of BB -- so relatively new cranks)? If you can find cranks that work with your current BB, it'll save you a few bucks, but you might look for a deal on a crankset/BB combo to ensure a good match between the two.
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Old 02-24-09, 11:40 AM   #4
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Quote:
Originally Posted by maxbicyclemax View Post
What are some of the important measurements of bottom brackets, threads, width, brearing sizes etc.

So if i want to change my "mmm, sora" crankset on my giant, do i have to stick with Shimano??

i see on ebay brands like, Raceface, FSA, Sram etc what measurements need to match, (i know about crank length)

anyone know of a website with exploded views of the BB?
Tell us what type of BB it uses. It's one of three kinds

1) Square Taper
2) Octalink
3) External BB

Ignore the last BB shown "ISIS", it's not that.



This is external.



The two black cups protruding from the frame.

If you are willing to change the BB out with a new crankset purchase than this whole issue is moot. Assuming you have a recent giant road bike. It's almost definitley a 68mm shell, british threading.

The rest of the specs you need for matching the bb, the crankset will tell you. For example what type of interface, required length etc.
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Old 02-26-09, 12:12 AM   #5
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hey thanks guys

yes it is a new bike 08, and yes it has external brgs
there is no clamp or shaft on the right/sproket side so id say spindal is part of the crank

so how do i remove the crank?
will only shimano crank/spindals combos fit into this BB?
68mm thread, how is that measured?

cheers guys
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Old 02-26-09, 12:41 AM   #6
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Here's the manual for your cranks http://techdocs.shimano.com/media/te...9830614887.pdf. You could change out with other Shimano road cranks, not sure about other brands with the road cranks, think Race Face interchanges fine.
68mm would be the width of your bottom bracket shell.
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Old 02-26-09, 07:58 AM   #7
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Basically, you choose a new crank, then choose the BB that matches. Has to have the right length spindle. If you spend enough, the newest cranks come with integrated BBs.
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Old 02-26-09, 12:08 PM   #8
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"If you spend enough, the newest cranks come with integrated BBs."

You DO NOT WANT integrated BBs, unless you've got PLENTY of $. Being able to swap out a $25 bottom bracket is infinitely preferable.
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