Couple quick answears on bars

[jdbubb@ix.netcom.com (Dan Bubb)]

Dan Smith wrote:
> 
> >From working in a bike shop, here's the difference between chromoly and aluminum. Chromoly has >thick, but small diameter tubes, where aluminum has the opposite.

Aluminum has to have a bigger cross section to make up for its lack of
stiffness, so this is the normal situation. Big tube with the minimum
wall thickness the manufacturer thinks he can get away without the tube
denting too easily.

> Aluminum is stiffer,

Aluminum may seem stiffer in the applications you're familiar with, but
the fact of the matter is the deflection of aluminum is 10,000,000
lbs/sq. in. and the deflection of steel is 30,000,000 lbs/sq.in. 
Aluminum is 1/3 as stiff as steel. The particular alloy is almost
irrelevant as far as stiffness is concerned. Pure aluminum is just as
stiff as 7075-T6 aluminum although nowhere as strong. Same with 1010
carbon steel vs. chromoly. Same stiffness, different strength. 

> lighter and doesn't rust but has zero give. Just my $0.02.

"zero give" is the same as zero deflection. Again, if you're talking
just about material properties aluminum will deflect 3 times as much for
a given load. Your experience takes into account design variations and
material properties. The material itself is more prone to deflection,
but the design variations compensate for this....in this application.

The other Dan
> 
> Dan
> 
> --- Neal Tovsen <nealtovsen@yahoo.com> wrote:
> >> Aluminum really wouldn't be a good choice for this
> >> part.
> >> Aluminum is ~1/3 the weight of steel, but it's also
> >> <1/3 as stiff as
> >> steel. So, the weight to stiffness ratio is roughly
> >> the same and you'd
> >> have to really bulk up the aluminum part to make it
> >> stiff enough to make
> >> it worthwhile.
> >
> >Ahhh...the same sorts of things could be said about
> >advanced composites. Yet F1 cars use aluminum and
> >composites more than steel, because that logic doesn't
> >take design into account. Comparatively oversized,
> >thin-wall aluminum tubing can be both stiffer and
> >lighter than steel. Autotech does this with their
> >strut tower bars. The concept was pioneered in the
> >bicycle industry by people like Cannondale.
> >Cannondale, Trek, and similar bikes are STIFF and very
> >lightweight. Conversely, I've seen (and ridden) some
> >cheap aluminum bikes that had steel-like tubing
> >diameters with thicker walls to compensate. As you
> >suspect, they weren't any lighter than a decent steel
> >bike.
> >
> >I think the stiffness of a well-built aluminum bar
> >would actually work better than steel for this
> >purpose, in addition to being lighter. Chromoly bikes
> >can be made to be almost as light as aluminum, but
> >they tend to have much more compliant (some would say
> >"spongy" or "springy", others would say "lively")
> >characteristics. Aluminum bicycles are often
> >characterized as being too stiff. Well, that't good
> >for us. We want a bar that is RIGID.
> >
> >If I only had a TIG welder...
> >
> >Neal
> >
> >--- Dan Bubb <jdbubb@ix.netcom.com> wrote:
> >> Aluminum really wouldn't be a good choice for this
> >> part.
> >> Aluminum is ~1/3 the weight of steel, but it's also
> >> <1/3 as stiff as
> >> steel. So, the weight to stiffness ratio is roughly
> >> the same and you'd
> >> have to really bulk up the aluminum part to make it
> >> stiff enough to make
> >> it worthwhile.
> >> Dan
> >>
> >> Bob wrote:
> >> >
> >> > Stock  is 3/4''with .125 walls this can be changed
> >> if people want to cut
> >> > weight, haven't got a weight yet
> >> > Kicking around the thought of a handfull of tig
> >> welded aluminum ones.
> >> > Price still haven't got that figured yet
> >> > Mounting to the same place as Kevins with a plate
> >> on top to spread  presure,
> >> > will come with all bolts.
> >> > Hope to have all things figured out tomorrow
> >> > Bob
> >> >
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