Butted Tubing Stiffer than Straight Gauge?



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Joe Stafford

Guest
I have a question. I recently asked a maker of nice titanium frames (they make a frame I am very
interested in purchasing) about their butting process and if they had a straight gauge tubing
options as well for heavier riders. I thought it might require some large diameter straight pipe to
get the stiffness in the BB for a heavy rider like me. I'm guessing the response I got was from
someone more involved in marketing than design. I'm going to call them to try and clarify this but I
wasn't to run it by you folks first to see if I am making sense. Maybe I'm wrong and they really can
do this with tubing.

The reply I got back they told me that straight gauge tubing is not stiffer than butted tubing and
listed their axioms of tubing stiffness.

1. Stiffness depends on the length of the tube.
2. Stiffness depends on the diameter of the tube.
3. Stiffness depends on the thickness of the end section of tube that joins the tubes.
4. A butted frame will always be lighter than an equivalently stiff straight gauge frame.

I agree with the first two statements. But I am having trouble understanding how a tube that is
thinner in the middle than a straight gauge tube (of the same diameter) would be more
torsionally/laterally resistant than a heavier tube that is the same thickness for the entire length
of the tube.

Even if you could get tubing where the butted ends were much thicker than available in straight
gauge tubing, wouldn't the total stiffness of the tube be determined by the average wall thickness
over the entire length of the tube and not just the thickness at the ends of the tube.

Maybe a butted frame can always be lighter than an equivalently stiff straight gauge frame but I
would think then the butted frame would have to use larger diameter tubing to make up for the loss
of material in the tube. Or maybe the reduction in stiffness by going to butted tubing is so
insignificant as to be unnoticeable in frames using the same diameter tubing? In my frame size I can
apparently loose a pound of metal from the frame and still maintain the same stiffness and
durability.

Thanks

Joe
 
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Tim McNamara

Guest
In article <[email protected]>,
"Joe Stafford" <[email protected]> wrote:

> 1. Stiffness depends on the length of the tube.

Fundamentally a tube is a spring. Shorter springs are stiffer, all other things (like diameter)
being equal. I doubt that there's a huge difference in stiffness between a 55 cm tube and a 60
cm tube. There's a big difference between a 55 cm frame tube and a 300 cm frame tube, to be
absurd about it.

> 2. Stiffness depends on the diameter of the tube.

Larger diameter tubes are harder to twist (torque) and harder to bend until the wall thickness
becomes too thin ("beer can" effect). The use of larger tubes allows thinner walls to provide the
same stiffness, and usually some weight savings in the process.

> 3. Stiffness depends on the thickness of the end section of tube that joins the tubes.

Not so sure I buy this one. But the engineering types can address this.

> 4. A butted frame will always be lighter than an equivalently stiff straight gauge frame.

Well, tube sets of identical length and diameter will be lighter if butted versus straight gauge.
Let's not let them mix apples and oranges.

"Stiffness" is really a much overemphasized and overplayed issue in marketing. But then, since the
difference between most road bikes is pretty small, they have to hype something.
 
R

Robin Hubert

Guest
"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]rp.supernews.com>,
> "Joe Stafford" <[email protected]> wrote:
>
> > 1. Stiffness depends on the length of the tube.
>
> Fundamentally a tube is a spring. Shorter springs are stiffer, all other things (like diameter)
> being equal. I doubt that there's a huge difference in stiffness between a 55 cm tube and a 60 cm
> tube. There's a big difference between a 55 cm frame tube and a 300 cm frame tube, to be absurd
> about it.
>
> > 2. Stiffness depends on the diameter of the tube.
>
> Larger diameter tubes are harder to twist (torque) and harder to bend until the wall thickness
> becomes too thin ("beer can" effect). The use of larger tubes allows thinner walls to provide the
> same stiffness, and usually some weight savings in the process.
>
> > 3. Stiffness depends on the thickness of the end section of tube that joins the tubes.
>
> Not so sure I buy this one. But the engineering types can address this.
>
> > 4. A butted frame will always be lighter than an equivalently stiff straight gauge frame.
>
> Well, tube sets of identical length and diameter will be lighter if butted versus straight gauge.
> Let's not let them mix apples and oranges.
>
> "Stiffness" is really a much overemphasized and overplayed issue in marketing. But then, since the
> difference between most road bikes is pretty small, they have to hype something.

Especially when combined with "compliant" in the same breath.

--
Robin Hubert <[email protected]
 
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Ron Hardin

Guest
Reynolds double-butted 531 gives a very whippy frame, I can tell you that.
--
Ron Hardin [email protected]

On the internet, nobody knows you're a jerk.
 
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Todd Kuzma

Guest
Tim McNamara wrote:

> "Stiffness" is really a much overemphasized and overplayed issue in marketing. But then, since the
> difference between most road bikes is pretty small, they have to hype something.

If you mean ride quality, I'd agree. However, frame stiffness, particularly torsional stiffness is
quite important for larger riders and/or touring cyclists who will carry gear. A frame that is not
sufficiently stiff for its intended load can exhibit odd handling characteristics (from the 2 wheels
being in 2 different planes when the frame twists), chain rub, and high-speed shimmy.

Many frames today are designed to be lightweight and to accomodate racers: folks who are generally
fairly light and carry no gear whatsoever. This is not necessarily ideal for those who have other
requirements.

I rode one particular super-light titanium frame that I was able to noticeably flex when standing. I
could rub the chain on both sides of the front derailleur cage.

Todd Kuzma Heron Bicycles LaSalle, IL 815-223-1776 http://www.heronbicycles.com
 
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Tim McNamara

Guest
In article <[email protected]>,
"Joe Stafford" <[email protected]> wrote:

> I probably got a response from someone in marketing/sales who really doesn't have much knowledge
> about the engineering aspects of their frames and may actually believe in vertical compliance.

I don't know about IF specifically, but practically no small bike makers have engineers designing
their frames. They build bikes based on the lore of the trade and practical experience- which is not
to say that they can't build a good frame. Trek, Cannondale, Giant, etc. probably actually employ
engineers, draftsmen, etc. But it's very unlikely in a small shop like IF.
 
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Mark Hickey

Guest
"Joe Stafford" <[email protected]> wrote:

>The reply I got back they told me that straight gauge tubing is not stiffer than butted tubing and
>listed their axioms of tubing stiffness.
>
>1. Stiffness depends on the length of the tube.

As Tim said, this is pretty much a linear function - and not really important when comparing two
frames (the assumption being that both have to have similar length tubes to fit).

>2. Stiffness depends on the diameter of the tube.

This is very true, and tends to dwarf other considerations.

>3. Stiffness depends on the thickness of the end section of tube that joins the tubes.

Stiffness at the ends of a butted tube affects the stiffness at the ends of a butted tube - that is
inarguable. However, a thin center section doesn't really change its mind about how to react to a
torsional load based on the thickness of the ends - and since the center, thinner-walled section is
by definition "less stiff", that's where a lot of the flex will occur.

>4. A butted frame will always be lighter than an equivalently stiff straight gauge frame.

There are too many variables to be able to use the word "always". If the "equivalently stiff staight
gauge frame" is just exactly adequately stiff enough (but no more), removing material from the
center of the tubes is NOT going to make it stiffer (this should be obvious). In the real world, a
butted frame that's adequately stiff CAN be lighter than a straight gauge frame that's adequately
stiff. However, in that same real world, the drawbacks are that the tubes will be much easier to
damage (especially if they're thin-walled oversize tubes), and the cost of shaving each gram by
butting the tubing may far exceed the cost of shaving weight elsewhere on the bike.

>Maybe a butted frame can always be lighter than an equivalently stiff straight gauge frame but I
>would think then the butted frame would have to use larger diameter tubing to make up for the loss
>of material in the tube. Or maybe the reduction in stiffness by going to butted tubing is so
>insignificant as to be unnoticeable in frames using the same diameter tubing? In my frame size I
>can apparently loose a pound of metal from the frame and still maintain the same stiffness and
>durability.

You can lose significant weight (not sure about a pound - but let's assume that's the case). And
assuming they use larger diameter pipes, it's true they can make the frame as stiff as a straight
gauge frame (like one of mine f'rinstance). However, there's no way it's as "durable" - though
hopefully that's never going to be an issue (most riders try to keep from doing things that would
bend their tubes no matter how robust they are).

Please don't take ANY of the above as a knock on IF - from what I've seen they make really nice,
well-crafted bike frames that appeal to the "high-end buyer" with their nice aesoteric touches.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
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Joe Stafford

Guest
I wonder if butted frames actually fail more often in the field than straight gauge. I had
originally been leaning towards some straight tubed Ti frames from some small builders until I ran
into the IF. But for what they are asking for their frame, it would be nice to have some more
information about their design process and their tubing choices. I've actually ridden a friend's
large Habanero MTB, it was pretty stiff for a stock Ti frame but I still would have like to have a
BB a little stiffer than that as it did seem to rub a bit for me but it was stiffer than other Ti
bikes I've tried. Does the Habanero have even bigger diameter tubing options available on customs?

I checked around on the web today and found some interesting pages on Sheldon Brown's page regarding
Rinard's frame tests. In there he actually has two equivalently sized Holland frames, one butted,
one straight gauge, and lo and behold the straight gauge frame is about 25% stiffer in their tests.
It didn't say what the weight differences were, however, which would be interesting. At least
somebody did some tests.
 
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Matt O'Toole

Guest
"Tim McNamara" <[email protected]> wrote in message
news:[email protected]...

> I don't know about IF specifically, but practically no
small bike
> makers have engineers designing their frames. They build
bikes based
> on the lore of the trade and practical experience- which
is not to say
> that they can't build a good frame. Trek, Cannondale,
Giant, etc.
> probably actually employ engineers, draftsmen, etc. But
it's very
> unlikely in a small shop like IF.

Ah, but companies like Easton and True Temper *do* have real engineers, designing the tube sets the
small framebuilders buy.

Matt O.
 
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Joshua Putnam

Guest
In article <[email protected]>, [email protected] says...
> Reynolds double-butted 531 gives a very whippy frame, I can tell you that.

That would depend on *which* double-butted 531 you're using. My touring frames are anything but
whippy, being double-butted 531 1.0/0.7/1.0 -- the thin center section is as thick as the butted
ends of some racing tube sets.

--
j[email protected] is Joshua Putnam <http://www.phred.org/~josh/> Braze your own bicycle frames. See
<http://www.phred.org/~josh/build/build.html
 
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Mike Jacoubowsk

Guest
> Reynolds double-butted 531 gives a very whippy frame, I can tell you that.

Ron: I thought you only rode Huffys? Did you have one from the days when Huffy owned Raleigh for a
short time? Even then I don't think they ever used 531 in any of the Huffy-branded bikes... :>)

--Mike-- Chain Reaction Bicycles http://www.ChainReactionBicycles.com
 
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John Carrier

Guest
> I wonder if butted frames actually fail more often in the field than straight gauge. I had
> originally been leaning towards some straight tubed Ti frames from some small builders until I ran
> into the IF.

Doubtful. The failure prone areas are the welds and anyplace the tube is compromised for fittings (a
overstress-test Merlin frame failed at the shifter boss).

If you're in the market for a custom Ti bike, you might contact Tom Kellogg at Spectrum cycles. Very
nice bikes. His steel creations are pretty special as well.

R / John
 
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Todd Kuzma

Guest
John Carrier wrote:

> If you're in the market for a custom Ti bike, you might contact Tom Kellogg at Spectrum cycles.
> Very nice bikes. His steel creations are pretty special as well.

Tom's brazing and welding may be very good, but based on the "technical" articles on his website, I
wouldn't trust his understanding of bicycle science. He parrots nearly every bicycle myth out there.

Todd Kuzma Heron Bicycles LaSalle, IL 815-223-1776 http://www.heronbicycles.com
 
A

Appkiller

Guest
I go between 205 and 225 lbs (depending on when in the season you weigh me) and I can't grind the
chain into either side of the front der of my Paramount ti (essentially a Serotta Concours) when it
the der is properly adjusted.

This has been an un-compensated plug for Serotta, for your consideration.

And it is butted all over, seat tube, down tube, chain and seat stays. Not particularly light by
current standards (~3.5 lbs). Nice n stiff.

As an aside, I saw Waterford's top frame (R-33) is now 2.9 lbs of custom drawn True Temper OX steel.
I wonder if it would support my bulk?

App
 
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Mark Hickey

Guest
"Joe Stafford" <[email protected]> wrote:

>I've actually ridden a friend's large Habanero MTB, it was pretty stiff for a stock Ti frame but I
>still would have like to have a BB a little stiffer than that as it did seem to rub a bit for me
>but it was stiffer than other Ti bikes I've tried. Does the Habanero have even bigger diameter
>tubing options available on customs?

Depends on the age of that frame. The MTB frames are now built with a 40mm down tube, and it's an
option on any custom road or 'cross bike. It's also the tube that is used to make the 48 x 32mm oval
down tube.

>I checked around on the web today and found some interesting pages on Sheldon Brown's page
>regarding Rinard's frame tests. In there he actually has two equivalently sized Holland frames, one
>butted, one straight gauge, and lo and behold the straight gauge frame is about 25% stiffer in
>their tests. It didn't say what the weight differences were, however, which would be interesting.
>At least somebody did some tests.

That would make sense to me. Once you consider that the tubes in the main triangle in a straight
gauge ti frame only weigh around a pound and a half, it's easy to see that you're not going shave
TOO much weight from them unless you make the walls "silly-thin".

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
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Joe Stafford

Guest
Mark,

I think that particular frame was purchased in 2000. When did the change occur in the tubing?

> Depends on the age of that frame. The MTB frames are now built with a 40mm down tube, and it's an
> option on any custom road or 'cross bike. It's also the tube that is used to make the 48 x 32mm
> oval down tube.
 
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Mark Hickey

Guest
"Joe Stafford" <[email protected]> wrote:

>I think that particular frame was purchased in 2000. When did the change occur in the tubing?

As I recall it was in '98 or '99. Certainly before 2000.

>> Depends on the age of that frame. The MTB frames are now built with a 40mm down tube, and it's an
>> option on any custom road or 'cross bike. It's also the tube that is used to make the 48 x 32mm
>> oval down tube.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
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Andy Dingley

Guest
On Fri, 9 May 2003 23:22:38 -0400, "Joe Stafford" <[email protected]> wrote:

>I have a question. I recently asked a maker of nice titanium frames (they make a frame I am very
>interested in purchasing) about their butting process

Don't ask Ti frame makers questions about butting. Ti is such a pain to work with that it affects
such "obvious" choices like seamless tube over welded, or the use of butting. Some companies will
turn to flannel here and sell you all sorts of shaggy dog stories, rather than come out honestly and
say "We'd do it if we could, but you can't do that in Ti"
 
B

Bluto

Guest
"Joe Stafford" <[email protected]> wrote:

> The reply I got back they told me that straight gauge tubing is not stiffer than butted tubing and
> listed their axioms of tubing stiffness.
>
> 1. Stiffness depends on the length of the tube.
> 2. Stiffness depends on the diameter of the tube.
> 3. Stiffness depends on the thickness of the end section of tube that joins the tubes.
> 4. A butted frame will always be lighter than an equivalently stiff straight gauge frame.
>
> I agree with the first two statements. But I am having trouble understanding how a tube that is
> thinner in the middle than a straight gauge tube (of the same diameter) would be more
> torsionally/laterally resistant than a heavier tube that is the same thickness for the entire
> length of the tube.
>
> Even if you could get tubing where the butted ends were much thicker than available in straight
> gauge tubing, wouldn't the total stiffness of the tube be determined by the average wall thickness
> over the entire length of the tube and not just the thickness at the ends of the tube.

Their case for butted tubing is a good one, inasmuch as material strain is proportional to stress.
Bending stress concentrates at the joints in a bike frame, so the material in these areas
elastically deforms proportionally more than the less-stressed material in the center section of the
tube. Therefore thickening those areas of highest stress will have a more pronounced effect on
stiffness than evenly distributing a similar amount of additional material.

Torsional stress around the axis of a tube is dispersed along the entire length of the tube, so
butting does not effectively stiffen a tube against torsion.

In practice, it is much more economical to use straight gauge tubing to gain a little more stiffness
over a butted frame of equivalent end wall thickness. Structurally speaking, though, the frame would
be stronger, more durable, and even slightly stiffer in some respects, if it were made with a
heavier gauge of butted material.

As an example, in the same tube diameters and material, a .9mm wall straight gauge tubeset would be
stiffer (but no stronger) than a .9/.6/.9mm tubeset, but a 1.1/.8/1.1mm tubeset would probably be
stiffest and would certainly be strongest of the three.

Chalo Colina
 
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