Aluminium frames appear to be resurgent in challenge to carbon fibre frames, in both light weight, and compliance. Is this sensible with regard to durability, and longevity? Aluminium has problems in situations where it is subject to continual flexing, which leads to fatigue failure. (Sudden snapping.) Those of us into sea sports (windsurfing in particular) were continually having to replace alloy booms (built to unavoidably flex somewhat) on nearly a yearly basis, and blessed the day composites (carbon fibre) took their place. Carbon fibre, provided it does not exceed its design limits of flexing, is almost impervious to fatigue.
It will be interesting to see if these lightweight alloy bikes with higher compliance (comfort) now challenging the role of carbon fibre (why, for goodness sake?) are indeed long lasting and durable? I would assume not! I used a Boardman Comp (£600) road bike originally but laid it up after 5 years use for fear of fatigue failure around the welds of the bottom bracket area. The current pair of carbon fibre bikes should be impervious to fatigue, apart crash failure, and should see me out.
M.T.B.'s successfully use alloy frames but they are not subject to smoothing compliance in that the full suspension plays that role, and the frames can be kept rigid. I see no downside in their design.
An interesting point and I concur totally with your concerns. I think in this context "compliant aluminium" is a functional oxymoron, since to be "compliant" it needs to be able to flex, which is going to kill it all the more quickly.
I had a Scandium alu frame (As thin walled as it gets) for seven years and it was still in A1 condition when I sold it to a guy who subsequently went on to race it.
People who question the safety of aluminium for frames are happy to ride about with alloy bars and stem, cranks, seatposts, rims and hubs etc without worrying about a catastrophic failure.
I think this is a legitimate question of application. IMO finishing kit is less stressed than other areas of the frame, while also typically better-placed to resist any cyclic loading it does encounter as it's typically made in one part, while the frames I've seen fail (including my own) have gone around welds which I imagine are already subject to stress concentrations from the welding process.
It's not like every ally frame is going to immediately drop to bits and kill its rider, however conceptually the concern is legitimate and far more relevant to ally than other materials.
This thread is cheerfully ironic to me as I just found horizontal scores on the upper inside of my nearly new giant aluminium road bike, which has a carbon fork - worried about the fork imploding under load, I was under the impression that carbon is less durable than metal
CFRP will degrade over time with cyclic loading as individual fibres break / fibre-epoxy bonds break down; however the fatigue limit of this material is far higher than others. The concern is that all this can go on with zero outward signs of impending doom; while of course the whole process can be hastened by one or more non-trivial impacts.
There's also the fact that its properties are anisotropic - meaning it's potentially very strong in one direction and really not so much in another - so when subjected to loading or impact in a direction other than those specifically accounted for in its design (such as a bike falling and the top tube striking the edge of something hard) the outcome is likely to be far more severe than it would be for an equivalent metal frame.
I have heard a few stories about giant frames cracking around the junction of seat and top tube , i reckon its something to do with the sloping top tube in their design in the earlier models .
Heard of 2 replaced by giant under warranty and seen another personally which i found and stripped for parts
Yes, this seems to be a popular mode of failure, and where mine went - on a bike that sadly pre-dated their more generous warranty provisions by several years.
Some thoughts as to what might have precipitated the failure in my case are mooted in
my thread on the subject..
