Re: Titanium vs Aluminium - relative weights

[James Annan]

James Thomson wrote:


> Are you suggesting that the carburizing could be responsible for
> eliminating the endurance limit in this steel?

I'm saying I read it on the internet (not specifically referring to
that steel, but in general). I don't know if it is true. It did
not seem implausible that surface hardening could increase
vulnerability to fatigue failure (cf anodised aluminium rims), but
I did not check it futher and am not an expert on this.

> Mostly though I take issue with prejudicial stuff like this:
>
> Oh, the myth purveyors have a ready list of excuses
> about how that test isn't fair, it picked on the poor steel
> frames, and in Real Life the steel would be bound to
> outlive the others. Steel is Real, after all, and they _know_
> that it doesn't fatigue, cos that old fart in the bike shop
> said so...
>
> SOP when prejudice comes up against evidence, sadly.
>
> You do know better.

Maybe, but I also know from the last year and a half's
tedious personal experience that there is always a vocal
element who will do their best to denigrate any and all
evidence that disagrees with their firmly-established
prejudices. It _is_ SOP when prejudice comes up against
evidence, and the quality of the evidence appears to have
little or nothing to do with it. There is not, and never
will be, a perfect test, but we have to use what evidence
there is.

Fortunately, in Real Life, even those who (initially)
disagree with me, are usually genuinely interested in
finding out the truth so tend to approach things with
a more open and objective mind.

James

 

[James Thomson]

"James Annan" <[email protected]> wrote:

> > > > > Furthermore, there are some steels used for bicycles that
> > > > > may well not have a fatigue threshold even in principle - how
> > > > > many steel advocates even know this, and which steels to
> > > > > look out for?

> > > When I wrote that, I had just found a page describing some
> > > deddacciai tubing as "lightly carburized" - whether or not this
> > > is enough to completely eliminate the fatigue threshold is of
> > > not course not known (to me). Oddly, I can't find that page
> > > again now.

> I'm saying I read it on the internet (not specifically referring
> to that steel, but in general). I don't know if it is true. It did
> not seem implausible that surface hardening could increase
> vulnerability to fatigue failure (cf anodised aluminium rims), but
> I did not check it futher and am not an expert on this.

That doesn't seem like a very impressive stick to beat those naughty steel
advocates with. I'd avoid waving it around in public if I were you.

> > Mostly though I take issue with prejudicial stuff like this:

> > Oh, the myth purveyors have a ready list of excuses
> > about how that test isn't fair, it picked on the poor steel
> > frames, and in Real Life the steel would be bound to
> > outlive the others. Steel is Real, after all, and they _know_
> > that it doesn't fatigue, cos that old fart in the bike shop
> > said so...
> >
> > SOP when prejudice comes up against evidence, sadly.

> > You do know better.

> Maybe, but I also know from the last year and a half's
> tedious personal experience that there is always a vocal
> element who will do their best to denigrate any and all
> evidence that disagrees with their firmly-established
> prejudices. It _is_ SOP when prejudice comes up against
> evidence, and the quality of the evidence appears to have
> little or nothing to do with it. There is not, and never
> will be, a perfect test, but we have to use what evidence
> there is.

To me it looks more like a pre-empting - setting up a prejudice against
anyone who might disagree with the results of the test or have objections
to its procedures. A warning to those with doubts to keep their traps shut.
I think it makes it hard to proceed to a discussion that isn't
unnecessarily adversarial.

Of course there will never be a perfect test, but in using the evidence we
have, we have to weight it according to its plausibility. This test, "the
best available" - which, after all, only tests one example each of a dozen
different frames - could be made far more convincing by calibrating the
load with real strain data. Until that happens, I think every reference to
this test should bear the warning: "Caution! Questionable loads were used
in the production of these data." - though I can see that that isn't going
to happen.

> Fortunately, in Real Life, even those who (initially)
> disagree with me, are usually genuinely interested in
> finding out the truth so tend to approach things with
> a more open and objective mind.

Progress from initial Disagreement to final Truth.

I'm waiting for my list of hypothetical coincidences.

James Thomson

 

[James Annan]

"James Thomson" <[email protected]> wrote in message news:<[email protected]>...

> To me it looks more like a pre-empting - setting up a prejudice against
> anyone who might disagree with the results of the test or have objections
> to its procedures.

Just getting my retaliation in first

> A warning to those with doubts to keep their traps shut.
> I think it makes it hard to proceed to a discussion that isn't
> unnecessarily adversarial.

"Proceed"? Since when has there been a discussion on this topic that
was other than "unnecessarily adversarial"?

> > Fortunately, in Real Life, even those who (initially)
> > disagree with me, are usually genuinely interested in
> > finding out the truth so tend to approach things with
> > a more open and objective mind.
>
> Progress from initial Disagreement to final Truth.

We can hope, but more realistically, we can learn to ignore those who
are not interested in the truth.

> I'm waiting for my list of hypothetical coincidences.

Sorry Sir, the dog ate my homework.

How about:

1. That the spectrum of loads that a frame sees in normal use falls
entirely below the fatigue threshold of a steel frame. (I would
probably dispute that there _is_ a clear upper limit to the loads that
a frame experiences in normal use over an extended lifetime).

2. That a wide range of frames made from different steels, tube
gauges, frame sizes and assembly methods can all have fatigue
thresholds of approximately the same value.

3. That builders with a range of experience, training and skill level
can possibly design and build frames with endurance thresholds which
are reliably above the largest loads encountered, despite both of
these factors being not only unknown but effectively unknowable.
(Doesn't seem likely to me that the builders would have any particular
motivation for this even if they could do it - all that matters is
that the failure rate is adequately low in practice.)

4. That every steel frame that does fail in real life was "defective"
in some way, or else "abused".

5. That loads of a "reasonable" level (below the threshold of a steel
frame) will cause a detectable fatigue problem for well-built
aluminium frames that already survived 200,000 high-load cycles in the
test.

6. That the S/N curves of Al frames are systematically steeper than
those of steel frames (hadn't come across this until you suggested
it).

7. That the firm clamping of the head tube in the test leads to some
particular bias against the steel frames.

That do for now? Of course, these are not entirely coincident but
partially overlapping. I have yet to see any evidence in support of
any of them. Have you?
That's not to say there is no hint of truth behind any of them, of
course.

James

 

[James Thomson]

"James Annan" <[email protected]> wrote:

> Just getting my retaliation in first

A strong tactic! I'm taking notes.

> "Proceed"? Since when has there been a discussion on this
> topic that was other than "unnecessarily adversarial"?

Medium duly noted, and point accepted.

> > I'm waiting for my list of hypothetical coincidences.

> Sorry Sir, the dog ate my homework.

Don't let it happen again. Now go sit down.

> How about:

> 1. That the spectrum of loads that a frame sees in normal use falls
> entirely below the fatigue threshold of a steel frame. (I would
> probably dispute that there _is_ a clear upper limit to the loads that
> a frame experiences in normal use over an extended lifetime).

> 2. That a wide range of frames made from different steels, tube
> gauges, frame sizes and assembly methods can all have fatigue
> thresholds of approximately the same value.

> 3. That builders with a range of experience, training and skill level
> can possibly design and build frames with endurance thresholds which
> are reliably above the largest loads encountered, despite both of
> these factors being not only unknown but effectively unknowable.
> (Doesn't seem likely to me that the builders would have any particular
> motivation for this even if they could do it - all that matters is
> that the failure rate is adequately low in practice.)

> 4. That every steel frame that does fail in real life was "defective"
> in some way, or else "abused".

> 5. That loads of a "reasonable" level (below the threshold of a steel
> frame) will cause a detectable fatigue problem for well-built
> aluminium frames that already survived 200,000 high-load cycles in the
> test.

> 6. That the S/N curves of Al frames are systematically steeper than
> those of steel frames (hadn't come across this until you suggested
> it).

> 7. That the firm clamping of the head tube in the test leads to some
> particular bias against the steel frames.

The statements fall into two broad groups. One group concerns the question:
does a practical fatigue threshold exist in steel frames? The second: are
the conditions of this test likely to reproduce the results seen on the
road?

First group: 1,2,3,4

> 1. That the spectrum of loads that a frame sees in normal use falls
> entirely below the fatigue threshold of a steel frame. (I would
> probably dispute that there _is_ a clear upper limit to the loads that
> a frame experiences in normal use over an extended lifetime).

"Entirely" is only a condition if you insist on _eternal_ life. I'd rather
not deal in absolutes. All that's necessary in practice is that a
statistically significant weighted proportion of the load experienced by
the frame falls below the endurance limit. As an upper load limit for a
given frame, I'd suggest the minimum load required to macroscopically yield
it (bend it).

> 2. That a wide range of frames made from different steels, tube
> gauges, frame sizes and assembly methods can all have fatigue
> thresholds of approximately the same value.

I don't see why that should be a condition. Surely they only need to have
endurance limits above a certain significant minimum value.

> 3. That builders with a range of experience, training and skill level
> can possibly design and build frames with endurance thresholds which
> are reliably above the largest loads encountered, despite both of
> these factors being not only unknown but effectively unknowable.
> (Doesn't seem likely to me that the builders would have any particular
> motivation for this even if they could do it - all that matters is
> that the failure rate is adequately low in practice.)

Again, this is a condition for eternal life. The same remarks as number 1.
"Unknowable" I disagree with: It's possible to determine both
experimentally. Your parenthetical point is realistic, of course.

> 4. That every steel frame that does fail in real life was "defective"
> in some way, or else "abused".

That's a tricky one. In a sense it's valid, because you can define "defect"
and "abuse" to span the entire set of failures. If you assume that a steel
frame should (effectively) never fail unless defective, then one that does
fail that isn't defective must have been abused (overloaded).

On the other hand, it's also a truism for any material. If your frame fails
through no obvious defect in a lifetime you consider inadequate, you should
probably have bought a sturdier frame.

Second group: 5,6,7

> 5. That loads of a "reasonable" level (below the threshold of a
> steel frame) will cause a detectable fatigue problem for well-built
> aluminium frames that already survived 200,000 high-load cycles
> in the test.

That depends entirely on the relative frequency of those lower loads, of
course. We need a load spectrum.

> 6. That the S/N curves of Al frames are systematically steeper
> than those of steel frames (hadn't come across this until you
> suggested it).

I suggested this to account for the possibility that the test results might
still be misleading _in_the_hypothetical_absence_of_an_endurance_limit.
That is, to reorder the results with a lower test load, the S/N curves
_must_ cross - either as a result of the curves of the different frames
having markedly different gradients, or because the steel (and titanium)
frames have an endurance limit.

In practice, I think we agree that the curves must and do cross. The
interesting question is where.

> 7. That the firm clamping of the head tube in the test leads to
> some particular bias against the steel frames.

That's not impossible. Restraints are much harder to model than loads, and
the less stiff frames would suffer more from an unrealistically stiff
fixture. This comes back to the need for a strain calibration.

> That do for now? Of course, these are not entirely coincident but
> partially overlapping. I have yet to see any evidence in support of
> any of them. Have you?

See above.

> That's not to say there is no hint of truth behind any of them, of
> course.

Of course.

James Thomson

 

[James Annan]

James Thomson wrote:

> "James Annan" <[email protected]> wrote:
>
>
>>Just getting my retaliation in first
>
>
> A strong tactic! I'm taking notes.

Don't come the raw prawn!

>
>>Sorry Sir, the dog ate my homework.
>
>
> Don't let it happen again. Now go sit down.

I consider my wrists slapped.

> "Entirely" is only a condition if you insist on _eternal_ life. I'd rather
> not deal in absolutes.

So would I. But (at the risk of being accused of settting up a
straw-man) it seems fairly common for people to make claims to the
effect that a well-built steel frame will last indefinitely whereas any
aluminium one will inevitably fail eventually. This is the claim that I
believe is at best extremely misleading and more likely just flat-out wrong.

I'm sure that there are some aluminium frames with poor lifespan and
steel ones with ample durability. But (for example) I'd back a
Cannondale tandem against anything, cos they have been around for a
fairly long time with a good share of the market and appear to have a
very low failure rate. Just heard from someone who has over 50,000 miles
on theirs - perhaps not huge by comparison with some singles, but a fair
use nevertheless (ours is at about 30,000 miles). They are not
particularly heavy, either.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

 

[James Thomson]

"James Annan" <[email protected]> wrote:

> I'm sure that there are some aluminium frames with poor
> lifespan and steel ones with ample durability. But (for example)
> I'd back a Cannondale tandem against anything, cos they have
> been around for a fairly long time with a good share of the market
> and appear to have a very low failure rate. Just heard from someone
> who has over 50,000 miles on theirs - perhaps not huge by
> comparison with some singles, but a fair use nevertheless (ours
> is at about 30,000 miles). They are not particularly heavy, either.

We're dangerously close to having one of those icky finding-common-ground
moments.

I've always thought Cannondale tandems were lovely, and if I came across
one of their early-nineties track bikes (metallic sky blue, steel
round-bladed fork, Suntour Superbe Pro group) in my size at the right
price, I'd snap it up.

They also have most of the elements in place to produce a Moulton-beating
small wheeled, fully suspended city bike, and are one of the few big
companies that are adventurous enough to actually bring it to market.

What I'd really like to see them make though is a fast touring frame with
geometry like the old ST500, 57mm calliper brakes, CAAD3 frame
construction, and a 1 1/8" external Aheadset. I'd buy one like a shot.

Then when it broke, I'd go right out and buy another.

James Thomson

P.S. Did you know that their lifetime warranty explicitly excludes fatigue
failure?

http://www.cannondale.com/policies/bike_warr_policy_ce.html

 

[Marten Hoffmann]

[email protected] schreef ...

> What I'd really like to see them make though is a fast touring frame with
> geometry like the old ST500, 57mm calliper brakes, CAAD3 frame
> construction, and a 1 1/8" external Aheadset. I'd buy one like a shot.

I don't know what the ST500 geometry was like, but how about the T2000?
It even sports a Brooks saddle
http://www.cannondale.com/bikes/05/ce/model-5TR2.html
Allright, it has cantilever brakes instead of caliper brakes, but still
.....


Or the more sports oriented Sport Road 800?
http://www.cannondale.com/bikes/05/ce/model-5RR8Y.html
This one even has caliper brakes!

> Then when it broke, I'd go right out and buy another.
>
> James Thomson
>
> P.S. Did you know that their lifetime warranty explicitly excludes fatigue
> failure?
>
> http://www.cannondale.com/policies/bike_warr_policy_ce.html

Makes you wonder what 'fatigue failures' are. Recently I witnessed my
first ever cracked Cannondale. This was a 2002 or 2003 Mountain Tandem.
The cracks started at the wishbone tube at the back. This is a flattened
tube in which they insert the rear rack bosses on the "short" side. When
they took it to the dealer who e-mailed photos to Cannondale Europe,
they were forbidden to ride one more kilometre! They received a new 2004
frame on which all other parts were bolted - at C'dales cost.

--
Regards,
Marten

 

[James Annan]

James Thomson wrote:


> We're dangerously close to having one of those icky finding-common-ground
> moments.

You can have a virtual hug and a kiss if you like - but only the
Parisian type, no tongues, this is a family newsgroup

> What I'd really like to see them make though is a fast touring frame with
> geometry like the old ST500, 57mm calliper brakes, CAAD3 frame
> construction, and a 1 1/8" external Aheadset. I'd buy one like a shot.
>
> Then when it broke, I'd go right out and buy another.

I have vaguely considered getting one of their road or touring bikes
several times, since they seem to be just about the only manufacturer
confident enough to build a frame that would fit me (largest size of
either model) but the lack of S&S couplers puts me off.

> James Thomson
>
> P.S. Did you know that their lifetime warranty explicitly excludes fatigue
> failure?
>
> http://www.cannondale.com/policies/bike_warr_policy_ce.html

I was aware of that, but I'm not sure how it works out in practice. It
certainly doesn't seem like a very clever bit of marketing.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

 

[Marten Hoffmann]

[email protected] schreef ...

> I was aware of that, but I'm not sure how it works out in practice. It
> certainly doesn't seem like a very clever bit of marketing.

Well, I can imagine that if a frame breaks after, say, 120.000 kms over
bad roads, fatigue is the principal cause of this. And in this case, it
is not unexpected. If it breaks after 120 kms, fatigue cannot be the
cause so it must be faulty manufacturing.

I would guess it somewhat protects C'dale from people who thoroughly use
their bikes and at the same time expect them to live forever. On the
other hand, C'dale might still decide in individual cases to reward a
warranty claim even when fatigue is probably the cause of a frame
breaking.

--
Regards,
Marten

 

[James Thomson]

"Marten Hoffmann" <[email protected]> wrote:

> I don't know what the ST500 geometry was like, but how about
> the T2000? It even sports a Brooks saddle
> http://www.cannondale.com/bikes/05/ce/model-5TR2.html
> Allright, it has cantilever brakes instead of caliper brakes, but still

Not nearly close. The ST500 was roughly 73 parallel in my size (58cm), with
a longer top tube than the new T2000 - closer to a road bike geometry with
longer chainstays. A 58cm Cannondale road frame fits me well, but the close
clearances really limit its usefulness. I'd have to get an extra large
T2000 to get the right top tube length, which (because of the sloping top
tube) would put the bars much higher than I like them.

> Or the more sports oriented Sport Road 800?
> http://www.cannondale.com/bikes/05/ce/model-5RR8Y.html
> This one even has caliper brakes!

Same problem I'm afraid. I'm also conservative enough to prefer an external
headset - although there are probably enough Hiddensets in use now to
guarantee spare parts for the foreseeable. And what were they thinking when
they chose those grotesque mudguards? (I assume they were thinking "D'oh!
We didn't leave clearance for real mudguards.")

Thanks for the suggestions anyway.

> > P.S. Did you know that their lifetime warranty explicitly
> > excludes fatigue failure?

> > http://www.cannondale.com/policies/bike_warr_policy_ce.html

> Makes you wonder what 'fatigue failures' are. Recently I witnessed
> my first ever cracked Cannondale. This was a 2002 or 2003 Mountain
> Tandem. The cracks started at the wishbone tube at the back. This
> is a flattened tube in which they insert the rear rack bosses on the
> "short" side. When they took it to the dealer who e-mailed photos
> to Cannondale Europe, they were forbidden to ride one more kilometre!
> They received a new 2004 frame on which all other parts were bolted
> - at C'dales cost.

I've heard similar stories. I guess it gives them the option of exercising
discretion depending on the amount of use the bike has had. A superlight
road frame returned after a dozen racing seasons might not receive the same
treatment.

James Thomson

 

[Marten Hoffmann]

[email protected] schreef ...

> Not nearly close. The ST500 was roughly 73 parallel in my size (58cm), with
> a longer top tube than the new T2000 - closer to a road bike geometry with
> longer chainstays. A 58cm Cannondale road frame fits me well, but the close
> clearances really limit its usefulness. I'd have to get an extra large
> T2000 to get the right top tube length, which (because of the sloping top
> tube) would put the bars much higher than I like them.

I see, you're after l-o-o-o-n-g frames

> Same problem I'm afraid. I'm also conservative enough to prefer an external
> headset - although there are probably enough Hiddensets in use now to
> guarantee spare parts for the foreseeable. And what were they thinking when
> they chose those grotesque mudguards? (I assume they were thinking "D'oh!
> We didn't leave clearance for real mudguards.")

Well, it's not quite Cannondale who invented these, rather it was SKS
(IIRC). And though not quite pretty - to say the least - I figure they
will keep road spray at bay quite well and will fit practically any road
bike w/o fender clearance.

> Thanks for the suggestions anyway.

My pleasure.

--
Regards,
Marten