Structural Integrity.
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Mustard



Joined: 28 Dec 2010
Posts: 306

PostPosted: Thu Nov 24, 2016 10:08 am    Post subject: Structural Integrity. Reply with quote

Yet again the structural integrity of modern lightweight bikes is brought into question. A 50 year old Australian man was killed when the alloy steering tube on his carbon fork catastrophically failed as he was pounding up a slight hill. His bike was several years old and had done a lot of miles.

The coroner questioned whether modern lightweight bikes should have a certified life span of safe usage? (Miles/age.)

The latest alloy bikes are lighter than ever, but despite the claims of superior alloy and all that, alloy has limitations with regard to flex, and fatigue failure. (As in aircraft, which use 'superior' alloy as a matter of course.)

Is there not a weight/strength limit below which it seems unsafe to venture, IF the bike is expected to last for a reasonable length of time, and/or miles?
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Robmet



Joined: 04 Jan 2010
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PostPosted: Thu Nov 24, 2016 6:02 pm    Post subject: Reply with quote

Interesting stuff.

Difficult to know where or how to draw a line, its also hard to predict what sort of life a bike will lead when it leaves the shop.
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Gunner



Joined: 15 Apr 2007
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PostPosted: Thu Nov 24, 2016 8:53 pm    Post subject: Reply with quote

Robmet wrote:
Interesting stuff.

Difficult to know where or how to draw a line, its also hard to predict what sort of life a bike will lead when it leaves the shop.



Totally agree.

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Roberto



Joined: 03 Jan 2014
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PostPosted: Thu Nov 24, 2016 9:44 pm    Post subject: Reply with quote

When I built my CR1 up the frame felt like it was made from toilet roll tubes, really scarily light.

Took a while before I stopped butt clenching when hitting pot holes Very Happy

Also, when torqueing up the stem on the carbon steerer I had to go well past the max torque otherwise the headset would come loose.

We have a local climb/descent with a cattlegrid half way down, hitting that at 30mph plus is so scary.

BUT ive also heard it said that the UCI lower weight limit of 6.8kg or 15lbs is outdated and bikes could be safe at much lower weight.

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Mustard



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PostPosted: Fri Nov 25, 2016 9:06 am    Post subject: Reply with quote

Obviously, that coroner would have been aware that how a lightweight machine is used (or abused) introduces an uncertain element in how it must react, BUT!

As Roberto said,how many 'hits' (potholes-cattle grids- cobbles- rough roads- all taken at speed) can a lightweight aluminium structure with all different weights of rider take before suffering fatigue failure? THAT could obviously be tested to destruction by the manufacturers. (Including lightweight carbon structures.) I believe some (Specialized for one) do their own internal tests, but surely there should be some independent agency to lay down riules.

It's also misleading for manufacturers to set arbitrary weight limits on riders, as though any weight which doesn't exceed that limit is safe, but any weight above it is unsafe. (Again, all depends on how hard the bike is ridden.)

What seems to be happening is that lightweight bikes are now seen as consumer discardables -i.e. constantly being replaced almost year on year by the latest and greatest and even lighter still must have! So what's to stop them pushing the boundaries?

Perhaps some independant authority needs to be involved with destruction testing as in other industries, setting out reasonable standards of safety. I believe some manufacturers (Specialized for example) test their own products so.

With the ever growing danger of more and more traffic, and often aggressive car drivers on the roads, any sudden bike failure could easily prove fatal. I find it odd that many renew crash helmets on a regular basis, whether they have been damaged or not, yet never give a thought to their thin tubed (skinny) bike failure!
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Richard A Thackeray



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PostPosted: Fri Nov 25, 2016 12:13 pm    Post subject: Reply with quote

Was it Kinesis, who recently issued a recall on certain forks, due to similar fears
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Robmet



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PostPosted: Fri Nov 25, 2016 2:59 pm    Post subject: Reply with quote

I think most of the bigger brands will have their own in house testing facilities, there are also the CE marks and associated tests and I think Germany has its own higher level tests for bicycles to be sold in Germany.

The problem is with structures that are designed to be as lightweight as possible then you are always going to reduce their overall capacity compared to more robust (heavier) structures. Is it a risk the consumer should be informed about and left to their own decisions? I know that personally I wouldnt buy a 2nd hand light weight bike, it would just play on my mind about its history.

Now my Supersix is coming up 4 years old i've started thinking about whether it should be replaced for basically similar reasons? Confused
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Richard A Thackeray



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PostPosted: Sat Nov 26, 2016 12:50 am    Post subject: Reply with quote

Robmet

I have a 1994 Dyna-Tech; one of the bonded titanium frames (the rest is 653)

After a Ridley superceded it, I used it as a commuter for several years, whilst it was retired/replaced by a Ribble (mainly because I wanted proper mudguards, & bigger tyres than '20' section) it was still going strong

It's still hanging in the garage, & barring a sticky right STI lever, it's a comfortable superbly handling bike

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Robmet



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PostPosted: Sat Nov 26, 2016 4:47 pm    Post subject: Reply with quote

Richard, I know the ones. My mate used to ride his until without warning one ride:



The downtube let go.
Shocked
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Gunner



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PostPosted: Sat Nov 26, 2016 7:36 pm    Post subject: Reply with quote

Shocked Shocked Shocked Shocked
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Richard A Thackeray



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PostPosted: Sat Nov 26, 2016 8:20 pm    Post subject: Reply with quote

Robmet wrote:
Richard, I know the ones. My mate used to ride his until without warning one ride:



The downtube let go.
Shocked

Mine's the road-bike

I was thinking more in terms of the life-expectancy of the adhesives used for the lug-to-tube joints
Then again, it was meant to be aerospace standard



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Roberto



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PostPosted: Sat Nov 26, 2016 11:14 pm    Post subject: Reply with quote

Robmet wrote:
Richard, I know the ones. My mate used to ride his until without warning one ride:



The downtube let go.
Shocked


That frame could easily be repaired with gaffa tape, the bigger problem is how did he stop the USE seatpost from sliding down its shim Laughing

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Mustard



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PostPosted: Sun Nov 27, 2016 8:51 am    Post subject: Reply with quote

Drill a series of small holes through the seat tube (as with alloy or carbon windsurfing extensions) and insert pin at required height. Doubt it would weaken it unduly.

Or, just wrap a few turns of Gorilla 'Gaffa tape' around it! Wink
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Robmet



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PostPosted: Mon Nov 28, 2016 11:25 am    Post subject: Reply with quote

Mustard wrote:
Drill a series of small holes through the seat tube (as with alloy or carbon windsurfing extensions) and insert pin at required height. Doubt it would weaken it unduly.

Or, just wrap a few turns of Gorilla 'Gaffa tape' around it! Wink


Not as much as the 1" gap in the downtube?
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Mustard



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PostPosted: Mon Nov 28, 2016 5:01 pm    Post subject: Reply with quote

I was joking about your 'bigger' seat post problem Rob. I had similar with a carbon one, but a couple of winds of tape around where it entered the seat tube did actually stop it slipping down.

As for the frame, well... I once bodged up an old bike frame snap by cutting a gap between the two parts to leave room to insert a couple of distance pieces (tube, for bolts, to stop crushing the frame tube) and drilled and bolted two strongish alloy shaped half tube plates, one either side, bolted hard up against the distance pieces with no free play between the holes and bolt sizes. (The tricky part.)

It actually held together for a try, but It wasn't really worth the effort (An old heavy bike.) But it filled a few hours of faffing and fiddling time, much preferable to sitting watching bleeding television!! Rolling Eyes
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