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arrive, at which point I will build it up from components. Question is, should I use a 3mm spacer on the right side of the bottom bracket? I read that someone had used a 3 mm spacer on the BB to reduce chainring rubbing on the 12, 13, 14, and 15, when on the 39 ring in the front. Is this a good idea? Do you need a wider BB (70 as opposed to 68), or can you use the same BB is you use the spacers?

Thanks,
 

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Miggity Mac Daddy
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Just FYI, the 70 vs 68 refers to BB outside diameter and is dictated by the frame. The spindle length, I think what you are referring to is usually 102-109 mm for a double and higher for triples.

In regards to the Giant frame needing spacers, I can't help you there. I suppose its a possibility if the chainstays are really short or something, making the angle tight, but a well adjusted fr. der should be clear of the chain. If its rubbing the fr. der. you could always trim it with the shifter a little to clear the chain. A well designed/well maintained frame shouldn't need spacers in the BB but I haven't really worked on a giant up close so for all I know, i could be dead wrong. Sorry, hope that helps though.
 

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You talking to me?
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736 Posts
Try it without the spacer first

packfill said:
arrive, at which point I will build it up from components. Question is, should I use a 3mm spacer on the right side of the bottom bracket? I read that someone had used a 3 mm spacer on the BB to reduce chainring rubbing on the 12, 13, 14, and 15, when on the 39 ring in the front. Is this a good idea? Do you need a wider BB (70 as opposed to 68), or can you use the same BB is you use the spacers?

Thanks,
It would be really easy to add the spacer after the fact if you have a problem with chain rubbing the FD. The spacer will probably run you about a buck so go ahead and buy it next time your order something or go to the LBS.

The 68mm and 70mm dimensions refer to the BB Shell width (left ot right). See pic attached (from Sheldon Brown). As far as I know your BB needs to match the BB shell width of your frame... but then again maybe a 70mm BB would work in a 68mm shell?

If you've got a really tight angle due to a short chain stay dimension you can also add a small washer to the bolt furthest towards the rear of the FD that holds the portion of your FD together that surrounds the chain. It doesn't get you much, but you probably don't want to mess with the width of the FD too much anyway.

Bryan
 
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