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PostPosted: Wed Feb 04, 2009 11:32 am 
Retro Guru
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Joined: Wed Dec 19, 2007 10:05 am
Posts: 961
Location: Brussels
Hi folks,
I've read in a few places that Truvativ GXP external bottom brackets use different bearings to Shimano/Race Face/FSA, and hence the BB units are interchangeable. However, I'm yet to find the details of how - or why - they differ.

Does anyone know what the difference is? Are they truly non-interchangeable? I have Truvativ GXP setups on two bikes, one BB is going fine but I seem to have killed the other rather quickly - though Belgian mud undoubtedly helped.

Cheers, Gareth.


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PostPosted: Thu Feb 05, 2009 11:09 am 
Old School Grand Master

Joined: Wed Jun 29, 2005 11:18 am
Posts: 15807
Location: near cwmcarn
I picked up a King BB a few months back. still totally smooth despite high mileage & no cleaning. I'll let you know how I get on..
Image


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PostPosted: Thu Feb 05, 2009 2:08 pm 
Retro Guru

Joined: Wed Aug 16, 2006 12:36 am
Posts: 586
The Truvativ BB on my cross bike is slowly dying. I was chatting to my friend who is a mechanic and he said that the diameter of the shaft is not uniform on truvativ cranks and the bearing size differs between left and right cups.


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PostPosted: Fri Feb 06, 2009 8:53 am 
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Joined: Wed Dec 19, 2007 10:05 am
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Location: Brussels
After reading the above response, I poked around a bit and by the power of google found this article:

http://www.velonews.com/article/85783

written by Lennard Zinn, who knows a thing or two about the tech side. The actual question is more detailed and complex than mine but the gist of it is that, indeed the NDS bearing in the Truvativ setup is 2mm smaller in diameter than the DS, with the spindle diameter stepped down.

However, they use the same standard bearing on both the DS and NDS, which in turn is the same as on the equivalent Shimano/RF/FSA units - and presumably third party ones like King, Hope etc. The step-down is achieved via a plastic top-hat shim - which in principle can be removed from the old knackered Truvativ one and fitted to the shiny new 'standard' one.

Doubtless it'll be a little more involved than that, but I have a spare LX one in the shed so I'll give it a go over the weekend. Truvativ bearings don't have the best reputation (max. complement bearing + crap seal = premature failure) so it'll be good to see if Shimano fares better - or if it's actually possible to upgrade to King or Hope. Beyond that, now that the various diameters are known, it might be possible to retro-fit some decent bearings into the existing cups (eg Enduro bearings, like BETD do) and put it all back together.

Cheers, Gareth.


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PostPosted: Fri Feb 06, 2009 9:01 am 
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Joined: Wed Dec 19, 2007 10:05 am
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Location: Brussels
By the way Scant, have you re-greased the King BB at all in that time, or has it just stayed naturally smooth?

EDIT: just seen the " ... no cleaning ...", must improve rudimentary reading skills :roll:


Last edited by garethrl on Fri Feb 06, 2009 9:25 am, edited 1 time in total.

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PostPosted: Fri Feb 06, 2009 9:10 am 
retrobike rider / Gold Trader
retrobike rider / Gold Trader
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Joined: Thu Dec 08, 2005 12:29 pm
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Location: London
I never thought I'd say it, but that King is a very sexy looking bottom bracket (I'll add my own fnar, fnar)


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PostPosted: Fri Feb 06, 2009 10:38 am 
Retro Guru

Joined: Wed Aug 16, 2006 12:36 am
Posts: 586
Interesting read. Let us know how you get on. I was primed to buy new cranks so I could avoid buing a Truvativ BB. If tranfering the shims is the only mod needed I'll buy a Hope unit.


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