Met a head on crash this morning, not a very fast one, around 30+ km/h, not able to fully stop in time and knocked the side of a car. Further inspection I notice a crack at the end of the top tube adjoining the headtube. Is the alu frame still safe to ride ?

Maybe just once, carefully, down to the Bike Shop, to buy a new replacement frame-set.

Bummer. Toast.

I'd be interested to ride it till it fails, because I'd really like to see how something like that does fail.

Not sure I'd be game, but I have a feeling it wouldn't let go catastrophically if the downtube still looks good. Hell, it might even hang together another few years. With zero peace of mind...

If you do decide to perform the experiment (I wouldn't advise it), it'd be a good idea to strip the paint off that part of the frame so you can keep an eye on the cracks and make sure there isn't one in the downtube.

IMO, there's a decent chance it'd let go under hard braking with the front wheel, which would not be graceful.

I expect an impact hard enough to crack the toptube also distorted the headtube and the headset no longer fits properly. Time for a new frame and probably a new fork.

I am a pretty careless guy, never using a helmet, running red lights regularly,,,,and I wouldnt ride it. lol

If it's toast, it's toast.
Sand off the paint for a better look.

If this were a steel frame, I'd say go ahead and ride it. Steel is relatively ductile, and the chances of a near simultaneous failure of the top and down tubes are near zero. I've seen steel frames fail after head on crashes, including my old 3-speed which took many years and thousands of miles before the downtube started showing serious signs of cracking (stopped when it was cracked more than halfway around).

OTOH- heat treated aluminum such as used on bike frames isn't very ductile at all and is very prone to notch failure. The upset under the downtube is essentially a stressed notch, and the tube will rapidly fatigue. When the tube goes, most likely not while braking, but from a bump while riding straight ahead, the top tube won't have the strength and ductility to survive, so you'd risk the front end coming off, with the main part of the frame plunging toward the ground.

I've ridden many dicey bikes, and have both seen and sustained frame failures, but the worst place to have one is at the fork crown, or a head tube separation are the most dangerous types because of the high likelihood of an endo.

Sorry to say it, but consider this frame toast.

Hi,

I'm just asking a question rather than disagreeing with what has been said :

Assumption (front to back is right to left):
A front wheel prang ends up putting a lot of anticlockwise tension in
the top tube causing any failure to occur on the top near the headset.

Proposition :
This is opposite to the normal stresses on the tube for riding and bumps.
Except for heavy front braking, essentially a milder version of the prang,
but front braking can't cause the high stress inertia allows in a prang.

Question :
Am I missing something thinking it won't rapidly get worse ?

Disclaimer :
If the damage is actually as bad as it looks from the paint, I would
never trust it, but I have heard of paint making things look worse,
(i.e. the paint cracking below the elastic limits of the tubing).

rgds, sreten.

Sreten,

Front wheels loads are all radial since it cannot pass any torque through the hub (disregarding side forces). So whether the line of force is upward (downtube under tension) or backward, (downtube is compressed) depends on the height of the bump or point of impact.

Draw a line from the point of impact through the axle and see if it passes forward or behind the lower fork bearing.to see which way it'll torque the head tube.

This same question of strike angle is why larger wheels are preferable on bumpy roads.

BTW- if you've ever roller skated, you know that a small bump about 2cm, high that your bike rolls over easily, is enough to stop your feet dead and through you on your face (if you don't step over it).

Hi,

You are of course right big bumps are not disimilar to running into something.

If that is your riding style you want a totally sound frame. I don't do bumps
of that sort on my bikes, except accidentally, or purposefully bunny hopping.

rgds, sreten.

I missed your point when I wrote the earlier answer. Under normal circumstances on a steel bike, this would barely matter. It would be worse with high strength alloys, since they're less ductile, but even they are fairly forgiving.

When it was the dominant material for good frames, riders with Reynolds 531 tubing would be very conscious that once the downtube was buckled, however slightly, the clock was ticking toward ultimate failure. But it still ticked fairly slowly, and when the frame failed, there would usually be decent warning by way of visible crack propagation.

What you're missing is that this is aluminum, and the rules are very different. The fatigue and notch failure properties of aluminum make it very unsuitable for riding with an upset in a critical area. The time to failure clock ticks much faster, and the time between visible crack formation and catastrophic failure can be very short,or zero.

That said, I've seen a few of these failures, including one with R-531 that we witnessed in slow motion (the downtube failed while we were still trying to convince the rider that it was happening, but the top tube held it together as the wheelbase got longer and the bike gently lowered to the ground like a kneeling horse). In all cases that I've seen, the downtube tube failed in JRA mode and the front wheel went forward, not backward as we'd expect if it happened during braking.

Updates: I just sand off the paint, and it doesn't seems there is a crack there. What you guys think ?

Huh.

I still think it's toast, only now you've removed the evidence. Wonder how it'd look polished?

I'm pretty sure heat-treated ally like this won't have survived well enough if the paint cracked. Even though it's intact, it'll be significantly weaker... ride at your own risk.

Selling or giving away this frame would make you culpable IMO, BTW

You're not looking for a crack at the top. These types of collisions rarely cause a crack.

The issue is the upset, or slight buckling at the underside of the down tube. It isn't a crack, and in the short term has almost the original strength. The problem is that aluminum is extremely prone to premature fatigue at notches, or local stress risers. So while it's OK today, it will rapidly and suddenly become not OK, and there's no reliable way to predict when that will be.

If you want to ride it for a short while, that would probably be OK but there are absolutely no assurances. Also when it does fail, it'll likely fail in both tubes in rapid (near instantaneous) succession. That means no support of the front of the bike as your fork and wheel fly off into space, and you do a face plant.

So if you do decide to ride it, know that the clock is ticking down to a nasty surprise, probably not today or tomorrow, or even next week, maybe not even next month or year, but sometime when you least expect it......

Hi,

Have a good feel around the top of the down tube and the front of
the toptube. You can often feel distorted stuff you cannot see.

I've read a lot about aluminium alloys and TBH I don't know. One viewpoint is all
aluminium alloy frames will eventually inevitably fail *, how long is how strong
its built and the style the bike is ridden. How much you have hastened the
demise of the frame I cannot say, though. But from what I understand if
its not distorted (the elastic limit has not been exceeded) it will not be
a huge amount compared to the constant pounding the frame gets and
the fact aluminium alloys have no fatigue limit and slowly harden until
they eventually crack, and that is usually pretty suddenly as well.

Its your call, carefully inspect the tubes, if you can feel anything don't risk it.

rgds, sreten.

* The aero industry simply retires planes after a certain air mileage.
I've read an aluminium racing frame is expected to last about 5 years,
but that to me is a how long is a piece of string sort of statement.

actually it's Hours in service.. pressurizing the cabin stresses them , as well ..

Hi,

Your right, service hours, for a particular plane = a typical mileage.
But I wonder is it the same for all (aluminium alloy) aeroplanes ?

rgds, sreten.

Well the guys that love those WW2 P51 fighters seem to keep them in the air for Pylon Racing,
until it kills them.


even on my Bicycle I get a greater Airspeed than I can Manage ground speed ,
with a headwind kicking my Butt ..


Those B52s that sit On Diego Garcia in the Indian Ocean seem to be up there in years ,
used for carpet bombing Viet Nam , during that Crime against Humanity...

but thats the bottomless military budget that has them rebuilt to be renewed often.

at taxpayer expense..

you are in UK ,remember the De Havilland Comet ?
they were to be commercial ,ca 1949.. a few came out of the sky
because the windows were made square.

seemed to be still in use by RAF , places like Kinloss in Morayshire , Scotland ..
at least when I was around there, [Forres], in '97.

Hi,

Being a Brit, of course, the worlds first commercial jetliner, 1949.

Went into service 1952.

The first version suffered from catastrophic metal fatigue issues after about a year,
though at the time it was cynically suggested to be a Yanks sabotage campaign.

mk2 improved the mk1, mk3 was a prototype., mk4 1958.

rgds, sreten.



mk4B 1969



The last flying version (2011) was the Nimrod, over 60 years after the
first version. The last mk4C commercial version was retired in 1997.

Yea, putting the Jet turbines in the Wing was slick, but that disallowed any Noise suppression technology
you find on the under the wing Planes, now, So each Take Off was a Really Loud occasion ..

Funny thing about that is the American navy had the same problem their steel ships where breaking in half and sinking.
They couldn't figure out why til they realised the square port holes where stress risers.Fifty years later it happened again
to the comet.