ALU- Frames - How long...

[twowheelsgood]

There was a long thread about this on the old C+ site. Basically fatigue stress on a modern frame would under normal use take around 110 years to be an issue. This came from the labs of one of the major manufactures (I think Trek). It's very unlikely a steel frame, even given care would last as long due to corrosion.

Early frames were not built well enough. It is generally much more difficult to build a frame in aluminium and more so again for titanium (usually has to be welded in a vacuum chamber!).

Presumably you all use steel wheels then because your lightweight aluminium rims go through a complete stress cycle every time the wheel goes around?

 

[asterix]

Aluminium rims are supported by spokes (steel on mine).

It is also interesting in this context that springs are almost invariably made from steel due to its resistance to fatigue.

 

[Smokin Joe]

What about cranks, brake calipers, stems and so on? Who uses steel because aluminium is likely to fail at any moment?

By all maean if you prefer a steel frame ride one, but let's forget this tosh about aluminium being an unsafe and short lived material.

 

[Milo]

Good I have an ALU bike was starting to get the fear then.

 

[Mr Pig]

What about cranks, brake callipers, stems and so on? Who uses steel because aluminium is likely to fail at any moment?

I agree, I wouldn't go back to steel. I'm doing to ask the next time I go into the bike shop what they've experienced, although many failures happen on older bikes that will never see a bike shop.

It's an interesting subject but a tricky one to find hard evidence about.

 

[Chris James]

Came to this late.

First off, aluminium alloys are good materials to build bike frames out of. Principally due to their low density and to a degree to thier corrosion resistance.

However it is true that al has a fatigue life and steel doesn't. The comparison between airframes and bike frames is unwarranted as airframes are not welded. They are rivetted and / or bolted, which limits the build of of stress due to the compression cycle. They can also be replaced modularly.

Likewise al has a good general corrosion resistance, but a poor localised corrosion resistance to road salts. Hopefully people with al frames also keep them clean!

An al frame is unlikely to spectacularly fail and simple inspection shoudl pick out any cracks developing.

As far as stems, seat posts etc being in al. These do not see the high stresses that a frame does. They are also cheaper to replace than a frame should they fail.

As far as rims go, anyone who has ridden a bike with steel rims know that they brake extremely poorly and would rather take teir chnaces with aluminium!

The life of an al frame is difficult to predict as it depends on the design and fabrication of the frame as well as its usage. In any case the average cyclists seems more interested in weight and constant upgrades than longevity.

 

[Smokin Joe]

I would take issue with some of those points. Bars, stems, cranks and particularly brake calipers must take more stress than a frame does.

 

[fossyant]

Don't get me started on alloy handle bars...... I ain't gonna say anything as my bars are 'well old'...........well used etc......

 

[Chris James]

I would take issue with some of those points. Bars, stems, cranks and particularly brake calipers must take more stress than a frame does.

Really? Look at the cross section of a crank for example and divide the force applied by your legs to get the stress experienced by the material.

Then think of how thin bike tubes are and how little area takes the force.

 

[Smokin Joe]

What about the force going through a brake caliper when a fifteen stone rider has to stop from 50mph on a descent? Or on the bars when you are out of the saddle sprinting?

 

[gbb]

This is not really going anywhere IMO...
It doesnt really need discussion whether alloy cranks, calipers etc are any good...they just are. As a rule of thumb, they've stood the test of time, and stood it very well.

Alloy frames....much the same applies, but it has to be said, the failure rate is higher.
Significantly so ?...probably not.
To a point where we should be concerned with modern frames ?...definately not. And thats from someone who has had an alloy frame failure.

 

[Chris James]

What about the force going through a brake caliper when a fifteen stone rider has to stop from 50mph on a descent? Or on the bars when you are out of the saddle sprinting?

Yes, lots of force. You are confusing stress and force though. They are not the same.

 

[Chris James]

This is not really going anywhere IMO...
It doesnt really need discussion whether alloy cranks, calipers etc are any good...they just are. As a rule of thumb, they've stood the test of time, and stood it very well.

Alloy frames....much the same applies, but it has to be said, the failure rate is higher.
Significantly so ?...probably not.
To a point where we should be concerned with modern frames ?...definately not. And thats from someone who has had an alloy frame failure.

I agree with this. I suspect early aluminium frame failures were due to inadequate tube thicknesses in order to take full advantage of the low density of aluminium alloys for light frames.

In the lght of experience they have probably bulked up the frames sufficiently to still maintain a weight advantage whilst keeping the practical working life of the frame long enough so they are unlikely to fail with normal use. Whatever normal use is.

 

[User482]

What about the force going through a brake caliper when a fifteen stone rider has to stop from 50mph on a descent? Or on the bars when you are out of the saddle sprinting?

What are the bolts holding the caliper to the frame made of?!

 

[Mr Pig]

Really? Look at the cross section of a crank for example and divide the force applied by your legs to get the stress experienced by the material.

Then think of how thin bike tubes are and how little area takes the force.

Interesting site:

http://materials.open.ac.uk/mem/mem_ccf.htm