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PostPosted: Fri Jul 20, 2012 8:28 am 
Retro Guru
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Joined: Wed Jan 28, 2009 11:50 pm
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Location: Where ever the beer (or Vodka) flows.
If your doing Time Trials on the road (or on the track), in the dry where every 1/10 of a second counts and you are going to strip every bearing after each event, then go for oil.
For bikes that get ridden everywhere, in all conditions, for the enjoyment of cycling (or commuting), I'd go for grease, seals, a bit more drag/effort and the longevity of components. :wink:


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PostPosted: Fri Jul 20, 2012 11:16 am 
Old School Grand Master
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Location: A veritable floating palace
Sadly, longevity of components isn't an accusation you could level at external bottom brackets, or indeed pretty much any modern bike component.


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PostPosted: Fri Jul 20, 2012 12:54 pm 
retrobike rider
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Joined: Thu Oct 14, 2010 1:33 pm
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Location: Brighton
what was the reason for the birth of external BBs? i kind of missed the whole revealing and they just seemed to appear on the scene for me...

is it more about weight saving?

to me, if i think about it, the stress is now concentrated on the 2 ends of the BB shell, rather than dissipated throughout the length of the shell and bottom bracket spindle....
i could be wrong, i've literally just spent about 10 seconds thinking about it.... :roll:


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PostPosted: Fri Jul 20, 2012 1:01 pm 
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Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8204
Location: New Forest, UK
The reason is that it allows a fat tube for the BB shaft. A larger diameter is stiffer. The outboard bearings allow the fat shaft to fir through a conventional frame. A better solution is to use a larger hole in the frame - like BB30.

Whether any of us need the extra stiffness is perhaps debatable. However the larger bearing should be able to take the loads better as it has more balls / rollers to support the load. The pitifully short lives of Octalink / ISIS BBs shows the effect of compromising by shrinking the bearings. However, fitting the bearing outboard does put it in the way of muck and introduces alignment and flex problems with the external cups.

Whether BB30 is a properly done solution I'm not sure - I've heard a few tales of failed bearings, which shouldn't happen if the idea is conceived properly.


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PostPosted: Fri Jul 20, 2012 3:55 pm 
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twain.......cost...........yes it looks all mr fancy pants, but it allows the makers to save on raw materals and offering you a lighter product for more money that lasts less.


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PostPosted: Fri Jul 20, 2012 10:47 pm 
BoTM Winner / Gold Trader
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Joined: Fri Feb 26, 2010 12:36 am
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Location: Burlington, ON Canada
hamster wrote:
The reason is that it allows a fat tube for the BB shaft. A larger diameter is stiffer.


Up to a point. I'm on vacation and my books are at work, but IIRC it is up to 50x (dia.vs wall thickness). After that you run the risk of impact or torsional collapse.


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PostPosted: Fri Jul 20, 2012 11:49 pm 
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Joined: Tue Feb 24, 2009 2:44 pm
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Location: Tamaris
twain wrote:
random thought, and please humour me on this.
could magnets (strong opposing types) be used to create frictionless movement on certain bike components such as bike pedal axles, wheel axles, headsets etc....


just sat here spinning a pedal at my desk and the thought entered my head.
would be cool to see a pedal spin on its axle all day long.....


As a kid I had an idea for a mag lev train after playing with some magnets, imagine my surprise when I found it was already being done with electromagnets. I also had an idea for a mag lev spring as a damper, this one electromagnetic so damping can be adjusted with higher current. I had loads of crap ideas as a kid.


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