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Old 08-23-08, 06:34 PM   #1
otakux
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Need help understanding bottom brackets

Hi I have a 2008 allez and I'm not so impressed with the stock crank that it came with and I want to replace it. I was would like to understand more about bottom brackets but primarily I would like to know what type would fit my bike. Thanks
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Old 08-23-08, 07:28 PM   #2
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Hi I have a 2008 allez and I'm not so impressed with the stock crank that it came with and I want to replace it. I was would like to understand more about bottom brackets but primarily I would like to know what type would fit my bike. Thanks
Since it's a Specialized, I'm 99.9% sure it accepts a standard English-threaded bottom bracket. Beyond that, you need to make the bottom bracket work with whatever crankset you want to put on the bike.

According to the Specialized website, there's 10 different "Allez" bikes, ranging from $700 to $3700. Maybe you just bought the wrong bike.
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Old 08-23-08, 08:41 PM   #3
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Maybe you just bought the wrong bike.
Wtf?

How does not being impressed with stock crank leads to "you bought the wrong bike"?

Anyways. The first thing the OP needs to do is select the crankset. The bb follows automatically.
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Old 08-23-08, 09:46 PM   #4
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The BB is the big shaft that holds both cranks. Ur not happy with the cranks, fine replace them, but u don't necessarily need to replace the BB, unless yer unhappy with that too.

BB = thick shaft with bearings.
Cranks = the arms.

The cranks are attached to the BB via big bolts.

Last edited by jsmithepa; 08-23-08 at 09:52 PM.
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Old 08-23-08, 11:03 PM   #5
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The BB is the big shaft that holds both cranks. Ur not happy with the cranks, fine replace them, but u don't necessarily need to replace the BB, unless yer unhappy with that too.

BB = thick shaft with bearings.
Cranks = the arms.

The cranks are attached to the BB via big bolts.
Assumes new crank will require the same type of bottom bracket standard and the same spindle length (does not apply to newer 2-piece systems).

Since bottom brackets are the much cheaper part, find the crank you want and get a new matching BB unless, of course, the old BB happens to match.
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Old 08-23-08, 11:31 PM   #6
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Being a 2008 I'd suspect that it uses either an ISIS or Octalink BB and cranks depending on who Specialized bought parts from that year.

If it's like my older Stumpjumper the Strongarm II cranks are Octalink compatible but hardly of exotic construction. I suspect from the dished out backside and the overall ( shaped cross section that FSA made them for Specialized.

A step up to one of the Shimano Hollowtech cranks would be a positive step up in rigidity and lighter weight all in one go. And assuming you have Octalink cranks there would be no need to replace the BB unless you want to go with one of the new external bearing types... which ARE much lighter and even more stiff.
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Old 08-23-08, 11:47 PM   #7
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According to the Specialized site, the Allez Triple and Allez Double use a square taper BB; Allez Elite Compact uses external bearings (w/2-piece crank).

If it's one of the lower-end models, I'd upgrade the BB standard if you're going to replace the crank anyway.
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Old 08-24-08, 06:08 AM   #8
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Being a 2008 I'd suspect that it uses either an ISIS or Octalink BB and cranks depending on who Specialized bought parts from that year.
Actually, none of the above. According to Specialized's web site, the two lower line Allez models use Suguino cranks (double or triple) and a "Sport" square taper bb. The Elite model uses a Tiagra 2-piece crank and a Suguino external cup bb.

By 2008, both Octalink and ISIS were pretty much out of fashion for new bikes. Shimano now makes only two Octalink road bottom brackets; the Dura Ace track-only bb and the 105-level for double and triple road cranks.
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