Alu Steerer Catastrophic Failure

[Greek Geeza]

Hi All,

Is it common for an Aluminium Fork to fail? The bike is about 2.5 years old. I had a front end collision with a pedestrian about 2 years ago, and the LBS inspected the fork when replacing the wheel: apparently all ok. I've had it serviced and safety inspected a few times since (in fact there was a free DR Bike event near work, so it had been inspected the day of the failure).

Looking at the break it was below the lip of the fork crown where the steerer is bonded to the forks. Even removing the fork form the head tube would not have shown a crack.

I'm a heavy guy (15.5-16 stone) but would have thought every day usage would not have resulted in such a failure. I don't race, just use the bike to commute to work. I don't jump curbs, but some London roads are a bit rough.

 

[RecordAceFromNew]

There are numerous sites on catastrophic failure of bike bits (especially carbon bike bits) but in this case some of the discussions on alloy component failures here may be of interest to you.

Typically a minute crack starts somehow which results in huge stress concentration at the tip of the crack, while cyclic loading cause the crack to grow over time until the thing fails eventually. The question that often requires difficult detective work is what caused the crack to form in the first place.

 

[Zoiders]

Hi All,

Is it common for an Aluminium Fork to fail? The bike is about 2.5 years old. I had a front end collision with a pedestrian about 2 years ago, and the LBS inspected the fork when replacing the wheel: apparently all ok. I've had it serviced and safety inspected a few times since (in fact there was a free DR Bike event near work, so it had been inspected the day of the failure).

Looking at the break it was below the lip of the fork crown where the steerer is bonded to the forks. Even removing the fork form the head tube would not have shown a crack.

I'm a heavy guy (15.5-16 stone) but would have thought every day usage would not have resulted in such a failure. I don't race, just use the bike to commute to work. I don't jump curbs, but some London roads are a bit rough.

You had a front ender bad enough to write off the wheel and the LBS didn't think it might have damaged an aluminium fork?

That's my problem right there - they should have advised replacing it. I also wouldn't be placing your trust in DR bike or anything that relies on volunteers as despite what people think I know from personal experience that not all of the volunteers are the brightest or best when it comes to anything beyond the most basic bike set up problems, they are well meaning of course but a lot of them may as well be volunteering in Oxfam.

When you had the front ender you have simply stressed the fork crown beyond it's fatigue life, sometimes this shows as a white patch on bare ally sometimes you see nothing at all, some times it fractures straight away and further use makes a small crack run - this is known as a stress riser.

First thing I would do is check the frame as well, look at and feel the underside of the down tube where it meets the head tube, if you find a ripple in the tube it's a good sign the ally frame could fail as well.

 

[Will1985]

Is this a full aluminium fork, or an alu steerer bonded to carbon legs?

 

[gbb]

You had a front ender bad enough to write off the wheel and the LBS didn't think it might have damaged an aluminium fork?

That's my problem right there - they should have advised replacing it. I also wouldn't be placing your trust in DR bike or anything that relies on volunteers as despite what people think I know from personal experience that not all of the volunteers are the brightest or best when it comes to anything beyond the most basic bike set up problems, they are well meaning of course but a lot of them may as well be volunteering in Oxfam.

When you had the front ender you have simply stressed the fork crown beyond it's fatigue life, sometimes this shows as a white patch on bare ally sometimes you see nothing at all, some times it fractures straight away and further use makes a small crack run - this is known as a stress riser.

First thing I would do is check the frame as well, look at and feel the underside of the down tube where it meets the head tube, if you find a ripple in the tube it's a good sign the ally frame could fail as well.

Its interesting...logic says you're right about the LBS probably should have recommended replacement....but, they may have given it a really good close look, saw nothing at all and with all good intentions, said it was ok.
I dont know if thats really good enough for such a critical component, but we'd all be mighty p1ssed off if every time we had a bump, the LBS recommended replacing all critical components.
I'm not knocking you here Zoiders , but for every fork that fails, there's probably 100 that continues their lives flawlessly...and there lies the problem.

I am very surprised DR whatsit didnt see anything on the day it failed. but then i'm not. It shows they just didnt look closely enough, or in the right area. I've checked my full carbon forks a couple of times, and a cursory glance just isnt good enough. I get light on the crown particually (and everywhere else), glasses on and REALLY look closely for anything that looks odd.

 

[Smokin Joe]

I've bent a pair of steel forks after a collision with a car, and that was with a front wheel which only needed mild truing afterwards. Any hit hard enough to write the wheel off is more than likely to muller the forks.

 

[Zoiders]

Its interesting...logic says you're right about the LBS probably should have recommended replacement....but, they may have given it a really good close look, saw nothing at all and with all good intentions, said it was ok.
I dont know if thats really good enough for such a critical component, but we'd all be mighty p1ssed off if every time we had a bump, the LBS recommended replacing all critical components.
I'm not knocking you here Zoiders , but for every fork that fails, there's probably 100 that continues their lives flawlessly...and there lies the problem.

I am very surprised DR whatsit didnt see anything on the day it failed. but then i'm not. It shows they just didnt look closely enough, or in the right area. I've checked my full carbon forks a couple of times, and a cursory glance just isnt good enough. I get light on the crown particually (and everywhere else), glasses on and REALLY look closely for anything that looks odd.

There are "bumps" and then there are "bumps that destroy the front wheel and involve a 16 stone rider"...

 

[gbb]

Oh yes, IMO, the initial 'bump' will have done the damage. But assuming the LBS did the inspection diligently and still couldnt see any crack (assuming the crack was even remotely visible), i guess it'd be usual to assume all was ok.
Considering OP has said its been looked at a couple of times since (not including Dr whatsit, cos they've obviously missed something that should have been visible on the day of the failure) whatever's happened with Ops forks, its remained hidden or not observeable to several inspections.

I'm a realist, where do you draw the line ? Hit a bad bad pothole and replace the forks ?, bump into a car and replace the forks ?. trouble is, we're all theorising when we didnt see the initial impact. i suspect if it was a hard one, i'd like to think i'd replace as a matter of course....but its knowing the strength of the initial impact that's unknown.

Makes you think ! Have i had an impact that'd make me even suspect the forks ? I inspect mine when ever i've got things stripped, i always have a good look at dropouts etc when deep cleaning...its a good thing to do.

In an ideal world, you're right Zoiders, no doubting that.

 

[Zoiders]

Newtons law old chap, if it destroyed the wheel then other damage would have followed.

The effect of the smash was observable even if the fork didn't fail straight away.

Yes it's had a hell of whack and the only way you can confirm something like that has caused damage is quite literally an x-ray as is done with aerospace componenets, not having an x-ray machine handy though - if there is a doubt then I am afraid there is no doubt.

 

[summerdays]

I wouldn't expect a Dr Bike to pick up non-obvious problems, they usually have a large queue of people with fairly basic problems to sort out - they aren't generally meant to replace a LBS's service. All the ones I have seen usually do lots of the run of the mill stuff such as cables, brakes, loose handlebars and things you point out that you would like them to look at (if they have the right spares/tools with them). A LBS service would take a longer period of time and be more thorough.

 

[gbb]

Newtons law old chap, if it destroyed the wheel then other damage would have followed.

The effect of the smash was observable even if the fork didn't fail straight away.

Yes it's had a hell of whack and the only way you can confirm something like that has caused damage is quite literally an x-ray as is done with aerospace componenets, not having an x-ray machine handy though - if there is a doubt then I am afraid there is no doubt.

Don't want to get into theroretical arguements , but apparently it wasnt observable for two years despite several inspections by LBS's who i assume were instructed to inspect because of the collision, and therefor should have been (and i would hope WERE) looking for just such damage, but despite this, no-one saw anything untoward.

Ah what the hell, i get myself into 'theroretical' arguements, but i'm not that bothered about it all, but its good to debate. The risk is there , we all know that. The difficulty is knowing the exact point when a collision will damage a component (any component) and whether that possible damage will display itself early on.

Regardless, it's a good post to highlight the dangers of impacts to critical components. The next question is, will anyone who reads this topic go out and replace the forks after any impact. They'll still never know whether it will be ok (and it may well be)..or not. Looking at the end result in this case, there's no argueing, you should.
But humans being what they are...they probably won't

Forgive me, i'm a realist. Hindsight has given us a concrete answer in this case..but this case only. We know where it led, we know what caused it in all probability. But how many people out there have had a collision (not neccessarily a heavy one) and never had a problem. Probably hundreds, maybe more. i remember once riding into the back of a car when i was a kid...i didnt have a problem with the bike, not immediately, not at a later date.

In the end, i'm not argueing the fact the impact damaged the forks, just the fact that the LBS were seen to have failed in not seeing something that wasnt visible, on several occasions. I think everything was done (by OP as well) to make sure all was ok. Sometimes, despite everyones best efforts, things slip through. Also worth bearing in mind when the LBS made their initial inspection, they dont actually know exactly how heavy the impact was.

Makes you think though...like i said, a good post from a saftey point of view.

 

[RecordAceFromNew]

Makes you think though...like i said, a good post from a saftey point of view.

+1, and in relation to secondhand bikes, or secondhand safety critical components, and hopefully without going into another long debate the relative intrinsic susceptibility to catastrophic failure of components made out of different materials.

 

[Zoiders]

The wheel was destroyed, that's observable even if a crack in the steerer isn't.

It's good indicator that not all is well in denmark and you should change the fork.

 

[gbb]

(semi in fun, semi seriously) And the handlebars ? and the stem ? If you take the logic to its end, who's to say the impact wouldnt have damaged the stem and handlebars. All that force going through them at the moment of impact.

Fkit, i'll buy a new bike if it happens to me. it'll be cheaper

 

[MartinC]

It's a judgement thing. If I'd had a an direct frontal impact that trashed the wheel on a bike with an alu steerer then I'd consider that changing the forks was a wise precaution. Changing bars, stem etc. is probably overkill 'cos they won't have subject to the sam impact. It's impossible to objectively quantify any of the risks in this but, in my opinion, this is the approach I'd expect from a skilled and knowledgeable bike mechanic.