Correct bottom bracket size question. Help please!
captain_vimes
Posts: 262
I recently bought two nice SAB carbon frames from Planet X but did not note the correct bottom bracket size from the details on the website when ordered and by the time I went back to check the adverts had gone.
Phoned Planet X and there we not that helpful saying they "were sure they were English 73mm, but had no way of checking" despite the information having been in the original advert.
Now I have a few spare brackets about so first offered up an English 68mm, which was too small as expected. So then I offered up an English 73mm, and this too slipped into the bottom bracket shell, being just too small in diameter to catch the threads! From simply this experience I think I need something like a 75 to 77mm diameter?
So what do I have here? The frames are road bike frames (one is 575 Racing, can't remember the name of the other). They are relatively modern, probably no more than 3/4 years old, and the rest of the SAB frames seem to be advertised as standard or oversize English threads?
I am not an expert by any means, but this really has left me at a loss.
Help please! :shock:
Phoned Planet X and there we not that helpful saying they "were sure they were English 73mm, but had no way of checking" despite the information having been in the original advert.
Now I have a few spare brackets about so first offered up an English 68mm, which was too small as expected. So then I offered up an English 73mm, and this too slipped into the bottom bracket shell, being just too small in diameter to catch the threads! From simply this experience I think I need something like a 75 to 77mm diameter?
So what do I have here? The frames are road bike frames (one is 575 Racing, can't remember the name of the other). They are relatively modern, probably no more than 3/4 years old, and the rest of the SAB frames seem to be advertised as standard or oversize English threads?
I am not an expert by any means, but this really has left me at a loss.
Help please! :shock:
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Comments
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73mm is the stated WIDTH.
English refers to the thread pitch and Diameter.
the 68 and 73 are the same diamter but work with different length BB Shells.
what happens when you try and fit incorrect BBs
http://www.sheldonbrown.com/gloss_bo-z.html#bottom"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown0 -
Opps! :oops:
Well I did say I was not an expert, but that is a bit of an embarrassing mistake.....
I will read up from the links and hopefully solve my problem from there.
Thanks for your swift replies!0 -
The original ads say "BSA" BB. So that's "English" threading, and as it's an older road frame almost certainly 68mm BB shell width. However an English BB is 1.37" diameter thread, equivalent to 34.8mm, and an Italian BB is 36mm diameter - so if you were offering up an English threaded BB it's possible it could just slip inside the Italian 36mm thread (as yours did), although Italian BB shells were usually 70mm.
Maybe take it to you LBS and ask them to identify the BB threads, but I'm leaning towards Italian threaded.0 -
Going to get me an Italian BB and give it ago.0
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Well remember that in that case both sides are "conventional" threads - ie do up clockwise.0
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It will be an Italian thread. Only the Italians use it and then only sometimes. BSA threaded BB will slip inside for sure.http://www.thecycleclinic.co.uk -wheel building and other stuff.0
