Butted aluminium tubes - Why?

[Brucey]

uh-huh...

If you take a butted tube and a PG tube and suspend them, when struck, they both will ring like a bell, quite nicely.

Funny that, isn't it?

So for my money, this idea of 'vibration transference being somehow different in butted tubes' and that this is somehow 'unrelated to the frame stiffness' is another one of these things that might well be fairy stories, but that get written in cycle magazines by lazy journalists anyway, with no substantiation whatsoever.

Note that the one thing that journalists have been unwilling to write for decades is that a more expensive frame is less stiff, because the idea that 'more stiffness is always good' has been peddled by them for so long. So they start waffling about 'vibration transference' and such instead.

I think that if you constructed two frames of identical stiffness using otherwise similar PG and butted tubes, that it wouldn't make any difference to the ride quality (even if they were different in other ways).

More usually there is a difference in the material properties and/or the frame stiffness, between butted and PG frames and this has a real effect; one that you can measure, and one that you can feel; no fairy stories required...

cheers

[Vorpal]

I'm with Brucey on this one. And actually I would argue that vibrations will transfer more easily in thin material than thick, as the additional mass will generally act to dampen vibration. Good tubes have a nice ring to them; I even made chimes from some scrapped frame tubes, once.

Heavier tubes, and soft steel do a good job of deadening vibrations, but that doesn't make for a better ride.

[sreten]

Hi,

FWIW the Youngs modulus, i.e. stiffness of a material doesn't vary much.

The strength does, by various treatments.

Ergo a lightweight high quality steel frame will be less stiff than a cheap steel frame.

Butting allows further weight loss without compromising joint
strength, and always inevitably results in a less stiff frame.

Alternatively, butting compensates for the reduction in the strength properties
of raw tubing caused by the jointing method, nowadays nearly always welded.

It is true alumunium frames are very stiff, because they have no fracture limit,
but they are not meant to be "stiff", its just that they generally are. Butting
allows you to shed weight, which will reduce stiffness, but it is still high.

"two frames of identical stiffness using otherwise similar PG and butted tubes"

Can't be done sensibly unless your comparing a plain tube road bike
to a loaded touring butted tube bike, i.e. if the same stiffness
the butted tube bike will be much stronger on the joint limits.

Butting is always a good idea. Not using it adds frame weight and as
side effect increases stiffness, but not strength. Fracture limits
mean aluminium frames tend to be a lot stronger and stiffer than
steel, by dint of the fact they tend to weigh about twice as much
as they would need to, to be equivalent to a steel frame, but
are still noticeably lighter than the steel frame, and a lot stiffer.

rgds, sreten.

Steel below a certain stress level does not fracture, (it does above).
Aluminium fractures to some extent at all stress levels, and so to
reduce stress alumininium frames are heavier than they need to be.

[Vorpal]

I think what you mean is that stresses below the fatigue strength in steel will not cause fatigue failures. That is breakage due to long term, repeated stress. Aluminum does not have a definite fatigue strength and will eventually fail in fatigue. The design of an aluminum bicycle must have sufficient strength to withstand a normal lifetime of repeated stresses. Welding introduces stress risers, and increases the likelihood of failure, which means yet thicker tubing.

What a normal lifetime of repeated stresses is, is entirely up to the company and it's designers. The capability of modern technology to predict such things is quite good.

[Brucey]

...indeed.

However, whilst it is possible to predict what the service stresses are in a certain geometry, it seems difficult to consistently produce that geometry, and not something that is much, much, worse from time to time.

In addition, the microstructure of the material (and therefore the properties) may deviate wildly from that used in any predictions, as might the levels of any pre-existing (residual) stresses. I've seen quite a few aluminium frames crack near the weld overlap regions and in these regions things are invariably much more horrible that you might expect.

So a (hopefully small) proportion of aluminium frames will fail prematurely, and none will last for ever. Hence my advice is to carry out regular inspections of your frameset if you don't want a nasty surprise.

cheers

[Vorpal]

...indeed.

However, whilst it is possible to predict what the service stresses are in a certain geometry, it seems difficult to consistently produce that geometry, and not something that is much, much, worse from time to time.

In addition, the microstructure of the material (and therefore the properties) may deviate wildly from that used in any predictions, as might the levels of any pre-existing (residual) stresses. I've seen quite a few aluminium frames crack near the weld overlap regions and in these regions things are invariably much more horrible that you might expect.

So a (hopefully small) proportion of aluminium frames will fail prematurely, and none will last for ever. Hence my advice is to carry out regular inspections of your frameset if you don't want a nasty surprise.

cheers

But a statistical analysis of manufacturing variations can be included in predictive models (variation simulation analysis); good process control can ensure that parameters remain within required boundaries. In theory, all premature failures, except those caused by abuse can be prevented. In reality, however, most companies either do not have sufficienct process controls to prevent all premature failures, or they specify tolerances that cannot be adequately controlled, rather than designing around actual, known capabilities.

[NATURAL ANKLING]

Hi,
http://www.williamsbikes.com/Material-T ... ep_45.html

Just wondering if some frame makers ditch the FEA stress analysis then carry on regardless.............

http://www.hera.org.nz/Folder?Action=Vi ... %20you.pdf

Edited -Aluminium frame.
http://www.wpi.edu/Pubs/E-project/Avail ... _Frame.pdf

[Vetus Ossa]

Interesting reading the comments on Vitus frames. I have had two 979’s and a 992 in years gone by and never found them flexible, though many seem to find them so. What I did find is that they were probably the nicest, most comfortable frames I have possibly ridden. For me they had it all, they were fast, handled well and above all were a superbly smooth ride. They all sadly had to go to make way for the next project as I needed funds for the build. I am seriously thinking about building another…anyone have a nice 53cm to sell?
I also had a Cannondale once, one of the ones with large tubes, and that was completely the opposite, it was so uncomfortable to ride on rough roads (read all roads) that it had to go.

[Keezx]

I've ridden an Alan frame from the late 70ties for a couple of months specially for the bumpy dune paths over here and really like it. The flex absolutely did n't bother me.
Sold it because it was 1 size too big.

[markyp]

My 52cm vitus 979 is a bit too rigid if anything. Maybe the larger frames were a bit flexy!

[Brucey]

My 52cm vitus 979 is a bit too rigid if anything. Maybe the larger frames were a bit flexy!

larger frames are definitely a lot more flexy; no doubt whatsoever about that. FWIW the one I had was a touch over 23" which would normally be too big for me, but the top tube was OK for length and the flutes on the campag seat pin came all the way out so I thought 'why not?' and rode it for a fair while.

cheers

[Des49]

I had a Vitus Duralinox 979 aluminium frame for a while. Since sold.
Superbly light and the ride was delightful.

I too enjoyed my time with a 979 frame, my first specific racing bike. Yes it flexed a bit but at the time I didn't think it affected me. Didn't own the frame long enough to check durability (it was stolen while racing in Ireland, of course Sean Kelly was racing one then too so I suppose this made it more desirable for some low life). I am sure I would have broken it sooner or later. One person I knew did have his frame break on the seat tube just above the bottom bracket half way through a hill climb.

From that frame I went to a custom built Columbus SPX frame, stiffer yes, but faster I cannot tell.
Still using this same frame 28 years on.

[willcee]

vitus , Now theres a conundrum, Sean KELLY arguably the most successful user of the FRENCH manufacturer , now raised from the ashes by Chain Reaction, was invited by the chairman of a local cycle club, and a good friend of mine, to address an off season club meeting while he was at home in Ireland, during winter months some years ago, he agreed and duly attended a well attended warm hospitable meeting and they had a question and answer session for much of the evening,Kelly, once in cycle company and off camera is a totally different persona than he appears in season and in harness.. asked about Vitus, the bikes mentioned here, he said that what annoyed him while he was contracted to the company was that every cyclist in Ireland and many in GB had strived to own one, and maybe just because he was doing great things on his, and he admitted that he broke nearly every one they gave him..!!!asked about a race where it was a critical time trial and he had ridden a road race bike instead of his TT machine, and amazed at the amassed memory detail.. he replied laughing, ''the fecking yoke broke while i was out warming up and they hadn't a spare, thats why''... on another matter i do have a 100 mile old... 56 vitus 979 with full super record, badged as dave kane cycles, immaculate and well over 30 years old here in my shed.. will

[RickH]

Continuing on the Vitus theme - I bought a 979 in 1988 (I'd traded my old road bike - a Hill Special - for a Muddy Fox MTB in 1988. Much as I like the MTB, & it has been my steed of choice in the snow today, I missed the road bike.

I really liked it & rode 10s of thousands of miles on it, up to & including a 2700 miles in 30 days (28 riding days) supported ride from San Francisco to Atlanta in '96. It even got much abused for several years as a commuter with Freedom Bikepacking Limpet low riders (U-bar that went on the QR spindle & velcro straps round the forks) for my stuff. Sadly it went walkabout (in a non functioning state) after several years of neglect in the mid-Noughties but I still have fond memories of it & the places I rode on it.

Rick

[willcee]

my vitus.. will