Aluminium frame longevity
Discussion
In the push bike world, aluminium frames have a limited lifespan of 5-10 years. I've never heard of this being applied to motorcycles, but given it's a similar material and even aluminium planes only last 30-40 years, so does this mean there'll be a day when my '96 VFR frame going to crack or worse still fail altogether?
it's very unlikely it will have a shelf life as such, frames on motorbikes although made of a material which does degrade somewhat over time are made with such huge tolerances as to make the damage done in normal activities through the flexing of the frame immaterial.
I would expect a frame that hasn't been involved in a serious crash to have an almost infinite life.
for example the engine block in my 1936 race car is made from Aluminium and provides the very flexible steel chassis with some extra rigidity, yet it's over 70 years old and does not have any cracks in it (as yet), even if it did crack, they could almost certainly be repaired.
There is a slight difference with bicycles as they are made to be a light as possible, and all aircraft components have some sort of shelf life, due to heat cycles, vibration, flex, risk aversion, etc, etc
I would expect a frame that hasn't been involved in a serious crash to have an almost infinite life.
for example the engine block in my 1936 race car is made from Aluminium and provides the very flexible steel chassis with some extra rigidity, yet it's over 70 years old and does not have any cracks in it (as yet), even if it did crack, they could almost certainly be repaired.
There is a slight difference with bicycles as they are made to be a light as possible, and all aircraft components have some sort of shelf life, due to heat cycles, vibration, flex, risk aversion, etc, etc
Edited by biffonracing on Wednesday 20th August 16:43
I can remeber this very question being asked by everyone when Suzuki launched the first alloy framed roadbike, the RG250 in 1983...turns out it was rather pointless, I never heard of any problems with those and a fair few are still on the road.
Slightly on topic, I did read in CB mag that the Steve Wheatman who has a collection of works RG500s, doesnt allow the carbon fibre framed bikes of the mid 80s to be riden because of concerns of the strength of those frames 30 years on..
Slightly on topic, I did read in CB mag that the Steve Wheatman who has a collection of works RG500s, doesnt allow the carbon fibre framed bikes of the mid 80s to be riden because of concerns of the strength of those frames 30 years on..
podman said:
I can remeber this very question being asked by everyone when Suzuki launched the first alloy framed roadbike, the RG250 in 1983...turns out it was rather pointless, I never heard of any problems with those and a fair few are still on the road.
Slightly on topic, I did read in CB mag that the Steve Wheatman who has a collection of works RG500s, doesnt allow the carbon fibre framed bikes of the mid 80s to be riden because of concerns of the strength of those frames 30 years on..
That's good to know. Though I have come accross some aluminium valve covers on cars with small cracks in, but I doubt they have the same factor of safety built in.Slightly on topic, I did read in CB mag that the Steve Wheatman who has a collection of works RG500s, doesnt allow the carbon fibre framed bikes of the mid 80s to be riden because of concerns of the strength of those frames 30 years on..
Funnily enough I've read carbon bicycle frames don't seem to have a fixed life span, it appears they're limited only by impacts etc. But then that contradicts the same logic for the aluminium frames which from that point of view you'd be correct, all very odd
VeeFource said:
That's good to know. Though I have come accross some aluminium valve covers on cars with small cracks in, but I doubt they have the same factor of safety built in.
Funnily enough I've read carbon bicycle frames don't seem to have a fixed life span, it appears they're limited only by impacts etc. But then that contradicts the same logic for the aluminium frames which from that point of view you'd be correct, all very odd
The problem with composites (especially older materials) is that they can be weakened by moisture and UV light. When they do fail, they tend to do so suddenly and catastrophically.Funnily enough I've read carbon bicycle frames don't seem to have a fixed life span, it appears they're limited only by impacts etc. But then that contradicts the same logic for the aluminium frames which from that point of view you'd be correct, all very odd
Aluminium work hardens when deformed, and cyclic stress can cause fatigue failures; there's a lot of history with this in old aluminium framed aircraft. However motorcycle frames are designed to be very strong and stiff, so fatigue is rarely a problem. On a push bike the entire frame visibly twists if you have someone mashing the thing up a hill, and given the thin wall tubing and general ultra-light construction, fatigue is more likely to rear it's head.
That's not to say alloy motorcycle frames are invulnerable, both Suzuki and Kawasaki have had to recall sports bikes due to some embarrassing frame failures.
Ooh, slightly worried now, as my alloy mountain bike is 15 years old now! Plus I am not a light lad, so I hope it won't collapse under me on a ride! 
The good news is, it seems fine still...
However....this isn't a totally stupid question, and I think it is probably down to the flexing and 'duty cycles' that metal might go through.
For example - aluminium aircraft airframes are limited by their 'compression / decompression' cycles. Once they've reached a certain amount of cycles, that is that, they are scrapped.
Anecdotally - back in my racing days, we did notice a degradation of handling characteristics after a couple of hard seasons. We always replaced all the headstock / rear arm bearings, plus mounts and suspension...but some frame fatigue did become evident after a while. The worst case we saw, was the frame starting to flex, to the extent that the top edges of the engine started to make gouge marks on the inside of the frame. Once we started to see those, we had to weld in one or two cross-braces.
But even after doing that, a two or three season-old frame often started to give us a few problems with suspension chatter, to the point that eventually, it had to be scrapped..
The good news is, it seems fine still...
However....this isn't a totally stupid question, and I think it is probably down to the flexing and 'duty cycles' that metal might go through.
For example - aluminium aircraft airframes are limited by their 'compression / decompression' cycles. Once they've reached a certain amount of cycles, that is that, they are scrapped.
Anecdotally - back in my racing days, we did notice a degradation of handling characteristics after a couple of hard seasons. We always replaced all the headstock / rear arm bearings, plus mounts and suspension...but some frame fatigue did become evident after a while. The worst case we saw, was the frame starting to flex, to the extent that the top edges of the engine started to make gouge marks on the inside of the frame. Once we started to see those, we had to weld in one or two cross-braces.
But even after doing that, a two or three season-old frame often started to give us a few problems with suspension chatter, to the point that eventually, it had to be scrapped..
Ray Luxury-Yacht said:
Anecdotally - back in my racing days, we did notice a degradation of handling characteristics after a couple of hard seasons. We always replaced all the headstock / rear arm bearings, plus mounts and suspension...but some frame fatigue did become evident after a while. The worst case we saw, was the frame starting to flex, to the extent that the top edges of the engine started to make gouge marks on the inside of the frame. Once we started to see those, we had to weld in one or two cross-braces.
But even after doing that, a two or three season-old frame often started to give us a few problems with suspension chatter, to the point that eventually, it had to be scrapped..
What kind of bike was that from if you dont mind me asking.But even after doing that, a two or three season-old frame often started to give us a few problems with suspension chatter, to the point that eventually, it had to be scrapped..
graphene said:
ianrb said:
The BMW S1000R has a recommended life of 80K miles.
Is that for the frame? Seems like an irrelevant figure considering how different the stresses could be according to how those miles are accrued.Is this really the case - I've got 2 bikes, both with 70+k on them. Bl00dy glad I'm expecting to have to put new frames on them.
as I recall from studies decades ago. Aluminium is different from steel when it comes to fatigue. Steel will only suffer from fatigue/stress issue if its loaded near its maximum strength (90%), whereas Aluminium will always eventually fail is subject to load cycles. Clearly with a low load is may be a very very long time. Anybody with a slightly less dusty/rusty knowledge care to comment.
Edited by balls-out on Thursday 21st August 13:40
I always assumed that if it was the case, manufacturers would warn of it. But then are they even liable if the bike's so far out of warranty? I doubt you'd get far suing for a car chassis which failed due to corrosion, but then they'd argue you could tell visually before hand during MOT etc.
How are you supposed to be able to tell when your headstock tube is going to fall off with a material which gives no apparent warning?
How are you supposed to be able to tell when your headstock tube is going to fall off with a material which gives no apparent warning?
Biker's Nemesis said:
Ray Luxury-Yacht said:
Anecdotally - back in my racing days, we did notice a degradation of handling characteristics after a couple of hard seasons. We always replaced all the headstock / rear arm bearings, plus mounts and suspension...but some frame fatigue did become evident after a while. The worst case we saw, was the frame starting to flex, to the extent that the top edges of the engine started to make gouge marks on the inside of the frame. Once we started to see those, we had to weld in one or two cross-braces.
But even after doing that, a two or three season-old frame often started to give us a few problems with suspension chatter, to the point that eventually, it had to be scrapped..
What kind of bike was that from if you dont mind me asking.But even after doing that, a two or three season-old frame often started to give us a few problems with suspension chatter, to the point that eventually, it had to be scrapped..
Oh, and after re-reading my post, we didn't 'scrap' the frames as such - we just sold the bikes
There are aluminium planes from WW2 still flying... it's down to applying suitable NDT techniques to areas under stress to determine what, if any, weakness is present.
Having seen pics of the airframes of Tucano trainers used by the RAF, I wouldn't be worried my bike was about to fall apart
Having seen pics of the airframes of Tucano trainers used by the RAF, I wouldn't be worried my bike was about to fall apart
balls-out said:
as I recall from studies decades ago. Aluminium is different from steel when it comes to fatigue. Steel will only suffer from fatigue/stress issue if its loaded near its maximum strength (90%), whereas Aluminium will always eventually fail is subject to load cycles. Clearly with a low load is may be a very very long time. Anybody with a slightly less dusty/rusty knowledge care to comment.
Close. Steel does have a fatigue endurance limit, usually around 40% of it's yield stress. So that means that if the stress is lower than this value, it will never fail due to fatigue, but if it's above it then it will. How many cycles it takes (one cycle = stress applied, then removed) depends on how high the stress is. Edited by balls-out on Thursday 21st August 13:40
Aluminium does not have a fatigue endurance limit. Put it through enough cycles and it will fail. (See generic graph attached - stress on y-axis in horrible units, cycles to failure on x-axis) Again the number of cycles to failure depends upon how high the stress is; keep the stress low enough and you'll be looking at millions of cycles to failure. In a big, rigid motorbike frame, this is probably the case.
If failure occurs, it shouldn't be sudden. You'll have cracks forming initially, which will gradually grow, before finally failing catastrophically. If you spot cracking (in high stress areas, headstock weld etc) then the frame has probably had it. Watch out for any big scratches/gouges in these areas, they provide ideal crack initiation points and can greatly accelerate the time to failure.
Edited by grahamr88 on Friday 22 August 11:35
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