Titanium and Frame Size

dhk wrote in message ...

Donald Gillies Wrote:
(Chalo) writes:

As I pointed out, there is no strength-to-weight advantage. Titanium
is desirable for its corrosion resistance and its high-tech glamor,
but has few other properties to recommend it over steel or aluminum
for bike frames.

Aluminum has a "zero" fatigue cycle endurance limit.

An Aluminum frames loses strength every time you ride it. Every
fatigue cycle is above the endurance limit, which is zero. Once you
ride an Aluminum frame enough times, IT WILL CRACK / FAIL.

Steel and Titanium has a "nonzero" fatigue cycle endurance limit.

If you ride a Steel or Titanium frame with stress levels below its
endurance limit, THE FRAME WILL BE IMMORTAL.

- Don Gillies
San Diego, CA

Correct in theory, except that few people buy a steel or Ti frame that
heavy anymore. I believe that lightweight steel or Ti at anywhere near
the weight of AL will fatigue and fail also. A quality AL frame at 2.5
lbs is going to last most of us longer than we care to ride it. You
could build a 5 lb AL frame that would last forever too, but there's
little market for them. To me, any comparison in life only makes sense
if you're comparing frames of equal weight.

I've got one of those "immortal" steel frames you talk about....a 531
lugged frame on my '74 Raleigh Gran Sport. Probably weighs a good 6
lbs, with a rock-harsh ride to go with it. I'm letting it rust in
peace.


How about its actual weight?

Trevor

"Donald Gillies" wrote in message
...
(Chalo) writes:

As I pointed out, there is no strength-to-weight advantage. Titanium
is desirable for its corrosion resistance and its high-tech glamor,
but has few other properties to recommend it over steel or aluminum
for bike frames.

Aluminum has a "zero" fatigue cycle endurance limit.

An Aluminum frames loses strength every time you ride it. Every
fatigue cycle is above the endurance limit, which is zero. Once you
ride an Aluminum frame enough times, IT WILL CRACK / FAIL.

Steel and Titanium has a "nonzero" fatigue cycle endurance limit.

If you ride a Steel or Titanium frame with stress levels below its
endurance limit, THE FRAME WILL BE IMMORTAL.

This is a very naive interpretation of the material science. It assumes that
steel/Ti frames are never stressed beyond fatigue threshold, which is
obviously not true since those frames crack and fail in use also. It also
assumes that the (calculated) fatigue life of an aluminum (or carbon fiber)
bike will be short relative to the actual years of potential use, also false,
since there are many old aluminum bikes in circulation that have been ridden
hard for many years. The fatigue curve for aluminum is *very* non-linear, so a
fairly small increase in material extends the fatigue life orders of
magnitude, making fatigue failure happen in relatively "infinite" time.
Lastly, it ignores the pragmatic reality that most frames fail from either a
design or manufacturing flaw, quality control and design soundness loom as
much larger reliability issues than material. Other factors to consider in
longevity are corrosion, impact damage resistance, and cost to repair, the
various materials have different tradeoffs in those areas, none being
obviously better in all respects.

"Donald Gillies" wrote in message
...
(Chalo) writes:

As I pointed out, there is no strength-to-weight advantage. Titanium
is desirable for its corrosion resistance and its high-tech glamor,
but has few other properties to recommend it over steel or aluminum
for bike frames.

Aluminum has a "zero" fatigue cycle endurance limit.

An Aluminum frames loses strength every time you ride it. Every
fatigue cycle is above the endurance limit, which is zero. Once you
ride an Aluminum frame enough times, IT WILL CRACK / FAIL.

Steel and Titanium has a "nonzero" fatigue cycle endurance limit.

If you ride a Steel or Titanium frame with stress levels below its
endurance limit, THE FRAME WILL BE IMMORTAL.

This is a very naive interpretation of the material science. It assumes that
steel/Ti frames are never stressed beyond fatigue threshold, which is
obviously not true since those frames crack and fail in use also. It also
assumes that the (calculated) fatigue life of an aluminum (or carbon fiber)
bike will be short relative to the actual years of potential use, also false,
since there are many old aluminum bikes in circulation that have been ridden
hard for many years. The fatigue curve for aluminum is *very* non-linear, so a
fairly small increase in material extends the fatigue life orders of
magnitude, making fatigue failure happen in relatively "infinite" time.
Lastly, it ignores the pragmatic reality that most frames fail from either a
design or manufacturing flaw, quality control and design soundness loom as
much larger reliability issues than material. Other factors to consider in
longevity are corrosion, impact damage resistance, and cost to repair, the
various materials have different tradeoffs in those areas, none being
obviously better in all respects.

"Donald Gillies" wrote in message
...
(Chalo) writes:

As I pointed out, there is no strength-to-weight advantage. Titanium
is desirable for its corrosion resistance and its high-tech glamor,
but has few other properties to recommend it over steel or aluminum
for bike frames.

Aluminum has a "zero" fatigue cycle endurance limit.

An Aluminum frames loses strength every time you ride it. Every
fatigue cycle is above the endurance limit, which is zero. Once you
ride an Aluminum frame enough times, IT WILL CRACK / FAIL.

Steel and Titanium has a "nonzero" fatigue cycle endurance limit.

If you ride a Steel or Titanium frame with stress levels below its
endurance limit, THE FRAME WILL BE IMMORTAL.

This is a very naive interpretation of the material science. It assumes that
steel/Ti frames are never stressed beyond fatigue threshold, which is
obviously not true since those frames crack and fail in use also. It also
assumes that the (calculated) fatigue life of an aluminum (or carbon fiber)
bike will be short relative to the actual years of potential use, also false,
since there are many old aluminum bikes in circulation that have been ridden
hard for many years. The fatigue curve for aluminum is *very* non-linear, so a
fairly small increase in material extends the fatigue life orders of
magnitude, making fatigue failure happen in relatively "infinite" time.
Lastly, it ignores the pragmatic reality that most frames fail from either a
design or manufacturing flaw, quality control and design soundness loom as
much larger reliability issues than material. Other factors to consider in
longevity are corrosion, impact damage resistance, and cost to repair, the
various materials have different tradeoffs in those areas, none being
obviously better in all respects.