Frame failure - your experiences please

Vantage

The dogs chew toy
I had a Proflex Attack LE Fail once. The main frame was 6061 alu but the rear triangle was chromoly. The rear chainstay cracked as a result of worn bushes which caused side to side play.
The LBS at the time sent it to Rainbow of Bury to have it welded and beefed up.
Then some scrote nicked it from my parents front garden as I was visiting them.
 

Milkfloat

An Peanut
Location
Midlands
I have only destroyed frames through accidents, I would count myself unlucky if one did go. However, most of my frames have a lifetime warranty which I would try to claim on if needed.
 

Globalti

Legendary Member
I've seen a few witness cracks on carbon frames especially older frames with thick glossy brittle paint, which cracked in areas of flexing. I've seen carbon frames damaged by sharp impacts and point loads. I've seen them snapped in high speed accidents. But I can't remember seeing a carbon frame that has just broken in normal use.
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
Any material has weaknesses, and TBH, it's never influenced my decision.

In 'the stable'

2 steel road bikes from early 90's - race and training bike.
1 steel MTB from early 90's
3 lower end Carrera and Ridgeback alloy MTB's
1 x alloy Pinnacle hybrid
1 x alloy and carbon fixie road bike
2 x alloy full suspension MTB's - one of which gets really used.

None have fell to bits, even the alloy/carbon fixie has been crashed a fair bit by cars - it's still intact.

Titanium bikes seem more prone to poor weld failures.

I wouldn't worry about the material used.
 

ColinJ

Puzzle game developer
I've seen a few witness cracks on carbon frames especially older frames with thick glossy brittle paint, which cracked in areas of flexing. I've seen carbon frames damaged by sharp impacts and point loads. I've seen them snapped in high speed accidents. But I can't remember seeing a carbon frame that has just broken in normal use.
Former forum member bromptonfb (and various other names) woke up in hospital with his family around him after the front of his CF mountain bike broke off in "normal use"!

Steel can fail if you let it go rusty. Here's a picture of the fork of one very fortunate cyclist that I met out on the road. He had felt his bike 'go wobbly' just after a steep descent and spotted this when he stopped to investigate...

dead_forks_large-jpg.jpg
 

Smokin Joe

Legendary Member
All those people who don't trust aluminium frames because they are "Weak" seem to be quite happy to stomp all their weight on aluminium cranks, pull violently against their aluminium bars and stem and trust their aluminium calipers to bring them to an emergency stop on a 50mph descent.

And to fly off on their holidays on an aluminium framed airliner.
 

roubaixtuesday

Über Member
I've owned steel, alu, carbon and Mrs T. has a Ti.

Two experiences of frame failure.

My steel touring bike cracked at the "ears" on both seat stays, after ~ 20 years and many 10s of thousands of miles.

Mrs Ts ti failed with a crack to the seat stay after far less usage, apparently a poor quality tube.

No failures on other materials.

So in my obviously unrepresentative and anecdotal experience, your trust in steel may be misplaced.
 

dan_bo

How much does it cost to Oldham?
Location
Failsworth
Former forum member bromptonfb (and various other names) woke up in hospital with his family around him after the front of his CF mountain bike broke off in "normal use"!

Steel can fail if you let it go rusty. Here's a picture of the fork of one very fortunate cyclist that I met out on the road. He had felt his bike 'go wobbly' just after a steep descent and spotted this when he stopped to investigate...

View attachment 504317
Good lad Sean.
 

ColinJ

Puzzle game developer
All those people who don't trust aluminium frames because they are "Weak" seem to be quite happy to stomp all their weight on aluminium cranks, pull violently against their aluminium bars and stem and trust their aluminium calipers to bring them to an emergency stop on a 50mph descent.
I've broken 2 aluminium cranks! :laugh:

Here's one I just cracked, though I'm sure it would have broken if I hadn't noticed the damage when cleaning the bike.

504321


[*** THIS is to save @Yellow Saddle having to tell me that I had overtightened the bolt! :laugh: ***]
 

FrankCrank

Professional layabout
Many moons ago, I broke the frame on my Raleigh Chopper, but it was used and abused in such a way that it was no real surprise. Jump forward a few decades, and this one happened very recently
1581554413483.png

It was a dozen years old or more, fairly light usage I would say, and the brand is not one you see nowadays. When I bought the bike, I recall reading that it was a rebadged Dahon, but this may not be the case. Anyways, it's replacement is a Raleigh Twenty from '77
 
When I volunteered at London Edinburgh London a rider turned up at Barnard Castle on an expensive steel bike.

Can't recall the make, but the crossbar had come out of the lug at the head tube.

He had fixed it with a chain of cable ties running around the head tube and seat post.
 
Location
Loch side.
I've broken 2 aluminium cranks! :laugh:

Here's one I just cracked, though I'm sure it would have broken if I hadn't noticed the damage when cleaning the bike.

View attachment 504321

[*** THIS is to save @Yellow Saddle having to tell me that I had overtightened the bolt! :laugh: ***]
Is this a challenge? I am now gonna tell you that you didn't overtighten the cranks....in a manner of speaking.

Cracked cranks don't really crack the way most people think they do. That's because it is impossible to crack a crank by overtightening the bolt in one go. If you install a crank right now and turn that bolt way beyond the recommended 40N limit and on and on, the bolt will break but the crank will be perfect. To understand how a crank eventually does break, I've designed this little analogy which I've been using in the Yellow Saddle Labs for years.
Look at this photo.

504341


The brush represents the crank and the dark surface represents the crank spindle. At this stage the crank is just installed loosely on the spindle and the bolt isn't in yet. As you turn the bolt, the crank quickly settles in a position where there is no more space between the crank and the square taper spindle and the fit is perfect. The straight-down bristles represent the fact that there's no friction between the crank and spindle yet and therefore no lateral force (left to right) between the crank and spindle. Everyone is happy, it's just nice and snug.

Now, we torque the bolt and this happens.
504340


The crank is being forced into a place where it doesn't want to go. The friction between crank (red) and spindle (grey) creates a force between the two that wants to push the crank to the right. Unfortunately for poor Mr Crank, he cannot move to the right because the bolt is pushing it left.
Eventually you settle on 40Nm of torque and the crank and bolt and spindle is in equilibrium with no more movement. The crank still feels the pain because internally, it is being pushed to the right. The fabric of the crank feels this ever-present force that wants to push it off.

Now you go for a ride. When you ride, you push against the crank and the square hole in the crank pushes on the spindle and the whole thing moves forward. But what's happening inside the crank is what's so interesting. At the four corners of the square taper, we're now changing the pressure pushing between crank and square spindle. At the leading edges of the square the crank is pushing harder against the spindle and at the trailing edges, pressure is slightly relieved.

Have a look at this sketch.

504343


The spoon shaped thing above is a nice Campagnolo aluminium crank. The square in the middle is the square taper crank spindle.

As the crank rotates cockwise, various points between crank and spindle change pressure. The arrows pointing towards the spindle indicates an increase in pressure and the arrows pointing away, a decrease.

Now imagine the crank interface as the brush above. At the beginning, before riding, all the bristles were bent backwards. But as soon as you put significant force on the crank, some of the bristles relieve pressure and return to the position in photo 1.

If you now stand on the crank when coasting, the opposite sides get relieved and so on and so on.

The nett effect is that the crank moves away from the crank bolt and further up the taper. That's because it is the only direction it can move to decrease pressure - the bolt prevents it from moving the other way and besides, the built-in pressure wants to be relieved in a certain direction only.

The crank crank thus tightens itself with use. Now Johnny DIY comes along with his fancy new torque wrench and during routine maintenance "ckecks" the torque on the crank and guess what, he finds it is only 20NM, not 40NM like in the beginning. The logical conclusion is that the bolt has loosened itself. However, it hadn't turned one iota, the crank distanced itself from the bolt and not it feels loose. DIY Johnny obliges, again and again, until the crank cracked.
 
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