Threaded versus threadless headset

Jennifer Donleavy writes:

Now that you mention it, that's the setup (with track clamp) I have
but I still don't like the way it performs. I climb hills standing
and find the forward reach of the stem and its 0.875 dia post an
unnecessary torsion bar between me and the bicycle.

Yeah, I know! Are those track clamps even available anymore? I
can't find one anywhere. Did you buy it recently or is it from the
old days?

I got my fork built with the split extension by a friend who has old
track bicycles with that sort of clamp. It's all SSTL anyway but that
doesn't stop the steertube from rusting just the same.

I'm looking forward to a new fork with suitable steertube to get
rid of that.

What about a steel stem? That's the solution I am considering --
having a tubular steel stem tig welded by a local frame builder.
Would that be a good, safe solution? Do they break from the notching
like I am expecting my current stem to do?

You can have mine when I get the new fork.

Jobst Brandt

Palo Alto CA

"Al Frost" wrote:

Besides if you are breaking your quills then you need to
take up a different activity.

Why, when he can buy a fork with a threadless steerer?

James Thomson

In article ,
(JP) wrote:

wrote in message
...
Al Frost writes:

That depends on whether the old system is a burden on maintenance
and safety. I'm going to change because I have had enough problems
with quill stems to warrant it. Besides, the safety margin in a
0.975 dia aluminum stem is nowhere near that of a 1.25 dia tubular
stem.

Now there's logic for you! Assuming that your 1.25" steerer and
your 0.975" quill were not hollow and there were made of similar
materials then your conclusion of a higher safety margin would be
sound. But they are not. The wall thickness of a steerer is much
less than that of a quill. Even though the outside diameter of the
steerer is much larger the quill retains it's strength with
increased wall thickness. Besides if you are breaking your quills
then you need to take up a different activity.

Oops! The strength of a round cross section is given primarily by its
outside diameter. That is why bicycle frames are made of thin walled
tubing instead of solid bars. Most of the aluminum inside the stem is
just excess weight. Meanwhile consider the thin skin of an aircraft.

Maybe we should make stems, and bicycles for that matter, from rolled
aluminum foil, then.

We would, except for the "beer-can effect" of too-easy denting. Really
light aluminum road frames and some MTB monocoque frames (the Norco VPS
bikes come to mind) already push the limits of frame wall thinness
against the limits of reasonable dent resistance.

The other limit is UCI regulations, which give a maximum diameter for
tubes, IIRC.

--
Ryan Cousineau, http://www.sfu.ca/~rcousine
President, Fabrizio Mazzoleni Fan Club

wrote in message ...
I got my fork built with the split extension by a friend who has old
track bicycles with that sort of clamp.

What is this track clamp?

It's all SSTL

??

(I'm feeling ignorant today)

"Bob M" wrote in message
news
On Fri, 22 Aug 2003 18:17:25 GMT, wrote:

Al Frost writes:



snip

I'd rather to be able to lower and raise the
handlebars (perhaps even during a ride) without taking 15 minutes to take
the stem off and switch spacers.
--

Cerebral palsy or some other dyskinesis?



--
Robin Hubert

"Bob M" wrote:

Personally, I cannot tell any strength difference between my quill stem on
my old Trek and the threadless system on my new LeMond.

--
Bob M in CT
Remove 'x.' to reply

This reminds me of my one experience with a broken stem. This was about 20
years ago when I was in junior high or high school. I pulled out the quill
stem on my bike and was shocked to see that the quill was in two pieces,
cracked all the way around. It was held together only by the expander bolt.
The crack was well below the level of headset locknut. I don't recall for
sure whether or not that was the first time I pulled the stem out (but
probably not), so I don't know if it broke during my use or earlier (the
bike was a hand-me-down). I put the stem back (deeper) into the steerer
tube and kept on riding that bike through high school. Not the smartest
thing, but I didn't have money and I figured it had enough unbroken quill
length to not to break again.

"Robin Hubert" wrote in message
ink.net...
"Bob M" wrote in message
news

I'd rather to be able to lower and raise the
handlebars (perhaps even during a ride) without taking 15 minutes to
take
the stem off and switch spacers.
--

Cerebral palsy or some other dyskinesis?

Best post of the day!

Bill "impressed" S.

Dianne who? writes:

I got my fork built with the split extension by a friend who has
old track bicycles with that sort of clamp.

What is this track clamp?

The steertube extends without threads above the head set, is split
and gets clamped with a ring and pinch-bolt.

It's all SSTL

Stainless steel abbreviated from the KBD.

Jobst Brandt

Palo Alto CA

In article ,
(JP) wrote:

Ryan Cousineau wrote in message
...
In article ,
(JP) wrote:

wrote in message
...

Oops! The strength of a round cross section is given primarily by its
outside diameter. That is why bicycle frames are made of thin walled
tubing instead of solid bars. Most of the aluminum inside the stem is
just excess weight. Meanwhile consider the thin skin of an aircraft.

Maybe we should make stems, and bicycles for that matter, from rolled
aluminum foil, then.

We would, except for the "beer-can effect" of too-easy denting. Really
light aluminum road frames and some MTB monocoque frames (the Norco VPS
bikes come to mind) already push the limits of frame wall thinness
against the limits of reasonable dent resistance.

So you're saying that ultra thin wall aluminum frames aren't strong
enough? At this extreme strength is not simply derived from the
diameter of the tubing, it's based on frame design, the way the tubes
are arranged, just as an airplane's aluminum skin would be inadequate
without its internal skeleton. Try folding an empty beer can. Its
weakness is not just observable as proneness to denting.

No, I'm saying that thin-wall aluminum frames are quite strong in the
ways that matter for a cyclist: they're stiff and resist being
compressed, flexed, or twisted. The arrangement of tubes on a UCI-legal
bicycle is largely fixed: there is little leeway for one design to have
a more rigid arrangement of tubes than another, for the same material in
the same dimensions.

The biggest constraint on making tubes as thin and large-diameter as the
normal stresses of a bike frame would prefer is that at some point you
would build a bike with featherweight, huge-diameter tubes, but the wall
thickness (being so much less important than the outside diameter for
determining rigidity) would be so low that the tubes would have too
little dent resistance. Dent resistance isn't part of what happens to a
bike when it gets ridden, but bikes need some dent-resistance so they
don't get dented when not being ridden, especially since dents in round
tubes (or in the wrong place on any tube) greatly compromise strength.

Empty beer cans do fold easily, but they don't need dent resistance at
that point in their life, and their walls are less than .013" thick.
Beer cans are remarkable structures, being very carefully analyzed and
costed, and a beer can is effectively a double-butted tube, with thicker
material at the top and bottom of the can. They are tremendously strong
for their weight, and a very optimized design. Internal gusseting can
make any design stronger, but for a given weight, it's not the way to
go, since you can get more strength (at least against torsional and
bending loads) by making the cylinder diameter larger.

Notes on aluminum cans:
http://www.psc.edu/science/ALCOA/ALCOA-light.html

Dent-resistance in aluminum cans:
http://www.psc.edu/science/ALCOA/ALCOA-model.html

An aircraft's skin is a stressed structure, a "monocoque" design. The
frame inside the skin is part of the structural strength of a plane, but
not as much as you would think. One important function the inner frame
provides is a place to mount interior fittings. Meanwhile the important
job of keeping the aircraft from twisting, flexing, or folding is done
mostly by the exterior skin, not the inner frame.

The other limit is UCI regulations, which give a maximum diameter for
tubes, IIRC.

Right. When you reach the UCI limit for tube diameter, you also reach
a limit for wall thichness beyond which strength will be inadequate.

Strength is a function of both tube diameter and tube wall thickness,
not to mention alloy and heat treatment properties.

It is, but the former completely dwarfs the latter, and the last two
aren't part of this discussion.

Let me put it to you another way: given the same amount of aluminum
(that is, the same weight, and of course the same alloy/heat treatment)
in two different round tubes spanning the same distance (say, 60 cm, the
top tube length of a large but typical bike), the one with the larger
diameter will always be stronger against torsion and bending, and Jobst
will correct me, but I think compression too.

The other tube will of course have thicker walls, but it won't be as
strong because diameter trumps wall thickness.

Now, "your" tube will take less damage if I take a hammer and try to put
a dent in the side of both tubes. And in the real world, I eventually
make "my" tubes so thin that they get crumpled by passing breezes,
aluminum foil style. At the point where the tube doesn't have enough
wall strength to resist ordinary wear and tear (you know, people
touching the frame , it will dent easily, and once it is dented, it
will no longer be a nice round tube, and its strength will be badly
compromised. Going back to the beer can analogy, it's easy to dent an
empty beer can, and a dented beer can is much easier to crush than an
undented one, because it collapses around the dent, causing more folding
and "dents", and then the thing loses all resemblance to a tube and
falls down.

That's not to say that I disagree with Jobst's conclusion that the
wider diameter stem will be stronger for a given weight, but I'm
guessing that the difference in strength between typical threadless
and quill stems is not a meaningful consideration, unless you are
pushing the design to its limit for weight savings. The bottomline in
the real world of off the shelf components is weight (and business
costs) versus adjustibility.

It's a positive attribute of a design which has other more important
advantages: threadless stems have no quill to seize or invisibly bulge
the steer tube. As several have already noted, these advantages are not
enough that most of us need to rush out and change our headsets, but all
things being equal, threadless is preferable.

As for the adjustability issue, stem reach is at least as important as
stem height for establishing a proper fit, but nobody seems to mention
that if anything, it is much easier to change out a threadless stem for
one of different reach than it is to change many threaded stems, since a
threaded stem without much excess cable may require detaching cables to
fully remove the stem. Not to mention that while removable-cap
threadless stems are nearly universal, removable-cap threaded stems are
at best only moderately available. If you're trying to get your
handlebars into the right position by adjusting the height without
changing the reach, you're just trying to get an ill-fitting bike into
the least-worst position!

--
Ryan Cousineau, http://www.sfu.ca/~rcousine
President, Fabrizio Mazzoleni Fan Club

Ryan Cousineau wrote:
...
Let me put it to you another way: given the same amount of aluminum
(that is, the same weight, and of course the same alloy/heat treatment)
in two different round tubes spanning the same distance (say, 60 cm, the
top tube length of a large but typical bike), the one with the larger
diameter will always be stronger against torsion and bending, and Jobst
will correct me, but I think compression too....

The compressive strength of both tubes will be the same. However,
slender structural members loaded in compression will fail by buckling:
i.e. the member will bow out in one direction (at which point it is no
longer loaded simply in compression, since bending moments have been
introduced.

The larger diameter tube will be more resistant to buckling, so it can
carry a greater compressive load.

Tom Sherman - Quad Cities USA (Illinois side)