Frame failure - your experiences please

swee'pea99

Legendary Member
Had a rear dropout snap once, at the point where it entered the main frame. Old steel frame, very lightweight, bought off ebay. No markings or decals - I think it had once been a team bike, specially made. Lovely thing it was. But when I bought it it had solid rubber tyres, obviously for awhile (they were very worn) and the ride was horrendous, as you might imagine. My theory was that the lack of pneumatic 'buffering' had overloaded that joint with impact-stress, leading to the failure. I kept it for a few years, hoping to find someone to fix it for me, but I never did and in the end I dumped it. :sad:
 
OP
wafter

wafter

Regular
Location
Oxford
Cheers guys - some proper horrors there but also some commendably high miles!

You're right to go with steel, more confidence inspiring.
The bird poop welding on the stays on your bike are an offence to my eyes although they have smothed the main tubes.
Thanks - I obviously think so although steel's clearly not without it's issues either. Didn't consciously notice the difference in the welds until you pointed it out, but yeah.. they're not the prittiest. That said it is an old, entry-level bike and the aesthetics of the welds are the least of its problems now!

Are you serious? Tell us more.
I don’t think carbon fibre frames degrade over time and are prone to fail, people shouldn’t peddle this nonsense.
I probably didn't phrase that very well as it implies poor fatigue performance which seemingly isn't the case providing its been designed correctly and made well. However, CFRP has its own set of perculiarities / weaknesses relative to metals, including:

- Anisotropic mechanical properties; meaning the materials' strength varies according to the direction of loading - making CFRP susceptable to damage if loads are applied in directions other than those principally accounted for in its design. A good example is the slew of examples of cracked seatpost tubes, seatposts and damaged steerer tubes due to people tightening seatpost clamp and stem bolts to torques intended for use on ally frames. Due to the fibre orientation in the the round sections involved, they're very strong under axial loading but very poor under radial loading.

- Poor impact resistance; meaning that unexpected impacts can be a lot more destructive to CFRP components than comparable metal items. Again plenty of examples on the net of CFRP frames that have fallen onto rocks / been hit against railings etc and failed as a result, when an equilvelent metal might have bent and certainly not failed catastrophically. This behaviour is worsened by the typical anisotrophy above.

- Greater potential for critical defects during manufacture due to increased complexity of process; such as inclusions / voids and porousity in the resin matrix.. which can serve as crack / failure initiation points and are very difficult to detect through inspection without specialist tools.

- Low strain to failure behaviour; i.e. the material exhibits little to no plastic deformation when loaded past its yield point so ofthen there are no visible signs of damage / impending failure until it goes bang.. unlike metals which will deform plastically (bend, dent etc) past thie yield point and give some sort of warning as result.

I also thought I read somewhere about a failure mode whereby over time fibres could break one by one / bonding could fail at the fibre / matrix interface (thereby reducing strength over time), however I can't find much on this subject relative to CFRP so perhaps it was in relation to another composite - most likely GRP.

So in summary I'm not saying CFRP is necessarily an inferior nor unsuitable material for bike frames, however it displays a lot of properties that require special consideration relative to metals, make me uneasy about my own abiity to assess its continued serviceability as the bike ages and hence diminish my confidence in riding it. We've all hit those massive unavoidable potholes in the past - personally on a metal fork I'd be confident that if it's not noticeably bent or cracked all's good; rightly or wrongly I don't feel the same about composite.

I found an apparently good example of sudden, low-load failure of a CFRP fork on this very forum, while Luscher Technic's youtube channel offers a lot of insight into the construction, assessment and failure of CFRP parts (his stuff on fork / steerer tube failure - like this one - makes pretty uncomfortable viewing tbh).


This one was interesting.

View attachment 504296
Wow - what's the story behind that? I'm guessing a big impact / landing..?

Never ever had a frame fail on me, ever. Must be something certain riders do to their bikes, maybe they are not so smooth in their cycling style or just too heavy for their bikes.
Not in my case; seatpost insertion good, rider mass in the mid-high '70 kgs.. unless I have a particularly waggly arse during the pedal stroke :tongue:

The night before the Cairgorm sportive which starts with a 45mph free wheel descent down from the Cairgorm Ski Centre I cleaned my Scandium Kinesis Gran Fondo to discover a massive crack on the right chainstay and almost identical one on the left chainstay :ohmy: Unfortunately it was just out of its three year warranty; Kinesis did give me 25% off a new frame which allowed me to afford a Ti Gran Fondo (I loved the Gran Fondo geometry but had doubts over another scandium).
That's a blow considering that it was only just out of warranty, although granted 25% is better than nowt as a gesture of good will.

I did actually contact the shop about my frame, but apparently it pre-dates the introduction of thier lifetime frame warranty. Bit disappointing given the lowish mileage but time-wise I guess I got my money's worth.

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.
Gutted - thieiving scumbags :sad:

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
Wow - that was a lucky escape by the looks of it :ohmy:

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.
Personally my issue is not that it's "weak", more that the effectively wears out through cyclic loading as at has no fatigue limit. To play devil's advocate I've never known modern, non-square taper cranks fail through this mechanism (few stress-raisers in the form of welds or sharp corners). I'd also guess that unless you're a complete powerhouse attacking huge gradients at low cadence the loading is probably negligeable.. might be different for downhill / MTB applications though.

Again bars see very little loading in normal use compared to the parts of the bike that support the bulk of the rider's mass, while calipers are usually pretty thick to give some stiffness, typically have few stress raisers and again I've never known them physically break in use. Besides, all of these parts are a lot smaller, cheaper and easier to replace than a frame.

I'd wager than your average commercial airliner is subject to somewhat more regular and rigerous inspection than your typical cycle, too ;)


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.
Thanks - looks like you might be right and I guess I was doomed from the off with my optimism re. Steel, although I still feel more confident in this material than the alternatives.

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
View attachment 504327
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
That looks pretty conclusive! Did it fail while riding? Did you escape unscathed? Looks like it could have caused a nasty accident...
 
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I buy my ‘workhorse’ bikes from Decathlon. They’ve all come with a lifetime warranty on frames, and a couple extended to forks. I’ve only had one failure where the weld on the top tube to head tube was. They replaced it with no quibbles. All the others have been fine. I’ve only got one CF bike, I’ve had it for 6 years, and it’s still going strong, with ( I really don’t know for sure but think it’s over 25000 ) miles on it, and I’ve been wiped out by a car on that one. I know of people with steel alloy framed bikes who have suffered failures far more readily. Remember folks “steel is real” so is rust:okay:
 
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Globalti

Legendary Member
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
View attachment 504327
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
Wow, that's a fundamentally bad design, all the weight and braking stress carried by one weld adjacent to the folding joint.
 
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I don’t think carbon fibre frames degrade over time and are prone to fail, people shouldn’t peddle this nonsense.
Absolutely right. There was some theories about the resin degrading over time, or the CF failing due to the mechanism entailed in it absorbing shocks in ‘normal use’, but none of it has been definitively proved. However, if you crash a CF bike, or shock it in ways that are outside of what could be termed ‘normal use’ the frames could ( and do ) start to change structurally significantly enough to cause noticeable differences / possible failures. But you almost certainly won’t get any deg, from normal usage / age.
 

Globalti

Legendary Member
Think of a bike frame tube as like a cardboard tube; if you can find a way to stress it without folding or creasing it, it's an extremely strong structure. But as soon as you add point loads in the form of an area of damage or something attached to the end you introduce stress risers and potential failure. It's the reason why the only way to tear Sellotape is to nick the edge with your teeth. As engineers like @Yellow Saddle will tell you, welding, especially if done badly, alters the properties of the material and introduces weakness at points of the greatest stress like tube junctions. That's why I like carbon frames; done well they are almost a rigid cardboard tube that has morphed into an extremely strong triangle with lovely smooth junctions to pass the stress through. But injure the tube with a sharp object and it's finished.
 

ColinJ

Puzzle game developer
Have a look at this sketch.

brush-3-jpg.jpg


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.
Is "cockwise" an engineering term for the rotation of penis-shaped objects, such as the crank in your diagram! :laugh:

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.
Aha... I AM 'Johnny' - I do just that.

Ok, I'll stop!
 

Jody

Veteran
I've snapped a frame at the head tube many years ago. It had taken an awful amount of abuse though.

I'm amazed how strong frames are these days, given the weight of a rider and how much force that puts through when you hit a pothole/jump/drops.
 

dave r

Dunking Diddy Dave Pedalling Pensioner
Another one here who hasn't broken a frame yet.
 

FrankCrank

Professional layabout
That looks pretty conclusive! Did it fail while riding? Did you escape unscathed? Looks like it could have caused a nasty accident...
Unscathed, luckily. Happened on a grassy area near the beach, just mounted the bike to pedal back to where I was staying, and it snapped clean in two. Mrs Crank had to fetch me in the car. The bike is now striped of usable parts, frame kept as a trophy.
 

MichaelW2

Veteran
I rode i to the back of mini on my Falcon Majorca. I bent the forks back but the frame was fine and lasted another 20 years before selling on. Modern forks are stiffer and decent frames use thinner metal do this may have been a write off for a different bike.
 

Ian H

I am an ancient randonneur, & I stop often for tea
Location
East Devon
I've broken one frame, an ancient steel Holdsworth. The top-tube snapped where I'd had a cable-stop brazed on. I found a handy piece of rope on the ground, tied head-tube to seat post, and rode the 12 miles home.

A friend, a man of considerable strength but less finesse, has over the years broken nearly every part of a succession of steel frames; even a head-tube once.
 
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