Re: 20 year-old stem and handlebars = flirting with danger?

hey peter

thanks for the detailed response. bottom line, you raise valid points.
i think however that we may be talking past each other a bit - we
don't disagree on everything.

that said, i'm kinda too tied up to give you the response you deserve at
this point, so forgive me. the points we should discuss some other time
are "high-alloy" & also strain aging, which i should have mentioned
before. later.

regarding philosophy on disposable bike components, you validly raise
the safety vs. economics question. again, that's a long debate, but
it's ultimately the consumer that decides what's what. if they won't
pay for certified defect free materials with guaranteed fatigue
performance, then they won't get it. period. you're right that
everything /could/ be better, but by that same analogy, we could all
drive cars with million mile engines for a modest extra cost, but noone
goes there. ultimately it's the market place that drives the product.

jb

Peter Cole said:

"jim beam" <[email hidden]> wrote in message
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Peter Cole said:

"jim beam" <[email hidden]> wrote

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>for two materials with the same work history, very roughly, yield is
>affected by composition. higher yield would indicate higher alloy.
>higher alloy reduces/eliminates fatigue endurance limit.

That's just a repeat of the same claim, still without examples.

peter, with respect, why don't you tell me /why/ i'm wrong? restating
your opinion does not qualify.

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Well, can you give some examples of frame tubing that has these
characteristics? 4130 variants are common in steel bike frame tubing, it's
been around for a long time and its characteristics are well known. Ditto

for

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the Ti alloys used.

why snip the relevant stuff? if you don't understand the principle, how
can you apply it in practise?

nothing's changed in the last 48 peter, answer's still the same. and
"4130" is not exactly dominant outside the u.s.

OK, your claim is that "high-alloy" steel doesn't have a fatigue limit.

Your explanation is:
"in principle, it works like this: in steel, fatigue endurance is due to
dissolved carbon being able to lock dislocations. at higher carbon
contents, the steel is no longer a simple solution but has multiple
phases, and these generally have a negative impact on an actual fatigue
endurance limit, even though they increase strength of the material."

"High-alloy" means a steel with more than 5% non-carbon ingredients.

You don't give examples of the alloys you're referring to, you do mention
Reynolds 853 and Columbus SLX, though only to say you don't have numbers.

SLX is/was apparently "Cyclex", about a 2% alloy, 0.27% carbon
The higher strength Nivachrome/Thermachrome are similar alloys, still not
"high-alloy".

853, True Temper OX, are "air hardening" steels. AerMet 100 is another. I
couldn't find composition data on the first two, but AerMet 100 is
"high-alloy" (~28%). I assume the compositions of the other two are similar.
AerMet has excellent fatigue charateristics.

I don't understand your reference to high carbon content. AerMet is 0.23%
carbon. Was there some other alloy you had in mind that is "high-alloy" and
high carbon, that exhibit this poor fatigue performance? How much carbon is
high enough to exhibit your claimed endurance reduction?

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I'm all for pushing the envelope in frames and many components, but bars,
stems, forks, cranks, and spindles (crank/pedal)? Nah, that's nuts.

that's your opinion. why don't you have a problem with other
consumables like tires? how about cars? they don't have infinite life
either & their cost is somewhat less insignificant than a handlebar.

I'm talking about safety, not economics. Reducing tire weight by 10% will,
roughly speaking, reduce the service life 10%. Reducing a handlebar weight 10%
will reduce its life 10x or more. It's a bad trade-off economically. It's
irresponsible from a safety POV. Average consumers don't understand
non-linearity. It's worse than meaningless to tell someone to replace bars
after X years, since that's not a valid measurement of fatigue life. You can
eyeball a tire to see what's left, you can't do that with a handlebar.