Handlebar failure likely cause?

[Jupestar]

Happened while going down a hill, luckily just me (no child) and I didn't come off.

It sort of folded off rather than snapped.

I assume primary causes would be

1) overtightened or unevenly tightened stem.
2) I'm too big and the bike is too small (it's my wife's bike - but it has the child seat, its a Small and i ride the XL).
3) I give it fairly hard use (when no child) as it's like a BMX for me!

It's had those handlebars/stem for about 3 years now and I don't think I've adjusted the stem recently...

Luckily it happened while I was riding it...

[gbnz]

I'd presume it'll have happened due to "heavy/intensive" use, on a relatively "lightweight" handlebar. The rationale for snapping near the handlebar stem, being that point will have additional stress placed on it.

I had a fairly new alloy handlebar (3/4 yr's old) snap out out of the blue 2/3 years back - twenty miles up the coast, on a dead straight, level section of road, that I invariably use as a short 1.25 mile recovery section on a 45 mile ride, taking it easy. Replaced it with a generic steel handlebar, which has been ok so far.

[Dingdong]

A more likely cause it's simply poor quality/OEM parts which are notorious for their quality assurance. At the end of the day, if any other bike part falls, it's simply an inconvenience. I've broken a handlebar myself previously,v on a small incline at low speed.

Almost killed me, broke two bones and a very nastybbang to the face. There is no more critical part in a bicycle! Except maybe for forks ..

[firedfromthecircus]

Also worth remembering that any sharp or protruding edges where the bar mounts in the stem will act as stress risers and give a potential failure point.
Heavy use and/or poor quality components as mentioned above will only be exacerbated by any stress riser issue.

Worth checking for before you fit a new bar.

[PH]

SNAP!
My snapped bars
viewtopic.php?t=112977&hilit=snapped

Five years ago and it still makes me nervous. I've been buying better bars, checking them periodically and being a bit more careful with the torque. Even so, Brucey described it as rotten luck, though points out that not all bars are manufactured the same, I think to a large extent I've accepted that's what it was, luck.
Mine went without warning on a flat stretch of road, the bars turned 90 degrees and I went flying over the other side of the road, where if a car hadn't acted quickly I'm not sure I'd still be here. It happened so quick I didn't even know that the bars had snapped till I'd picked myself up.
I thought mine would be a unique event, but it turns out it isn't that uncommon.

[foxyrider]

Also worth remembering that any sharp or protruding edges where the bar mounts in the stem will act as stress risers and give a potential failure point.
Heavy use and/or poor quality components as mentioned above will only be exacerbated by any stress riser issue.

Worth checking for before you fit a new bar.

+1

I've had most things break on a bike at some time but so far, touch wood, nothing in the handlebar/stem/fork area. Its not an issue exclusive to bigger riders but i'm pretty sure that 'giving the bars hard use' won't help and the current trend for ever wider straight bars doesn't help either.

For example, my mate, @ 2m tall and not someone to treat his bikes delicately purchased a nice Bontrager stem, set everything up to correct torque and went for a ride, nearly scared himself ~*%tless when he got out of the saddle as the bars felt like plasticine (other modelling clays are available!). He initially thought it was the bars flexing but further investigation showed it to be the stem twisting! Needless to say he found an oversize stem that doesn't flex - solves one issue but he's still swinging off the same length of bar so the stresses at the stem clamp must be horrendous.

In the past, failure of bars at the stem gave rise to sleeved bars, damage to the sleeve wouldn't affect the integrity of the actual bar, sadly modern bars eschew this feature in the pursuit of lightness.

[simonineaston]

Oh goodness - I didn't even know this could happen... I'm glad you guys survived!

[PT1029]

Can you post a close up photo of both fracture surfaces? Those of us who are metallugically inclined may be able to give a more precise cause.

+1 for checking stem clamps for sharp edges possibly forming stress raiser scratches.

If you have been giving them a hard time for 3 years (depends on how often you have borrowed the bike), Cinelli say that if you use their metal handlebars for (professional?) road racing/competition, they should be replaced after 3 years - not sure where that leaves us tourists using the same Cinelli bars for decades!
Appreciate your bars are not (probably) Cinelli, but it gives a clue as to what they think covers them.

[Jupestar]

Thanks for the replies. As a couple of posters said I'm going with general fatigue on them.

The clamps bolts came out easily enough, with a simple multitool. Stem bolts needed a bit more force, but that bit didn't fail.

Can't find anything on the stem which could have interferred with the bars, and the stem itself is in good condition.

Was tempted to take the (same) bars off my bike, which I use for DH (but I am rethinking using that now).

Instead I had an old Surly bar fitted to an RST stem which I forgot I had. Bike is even more BMX like now...

Will probably do away with the old stem just in case.

[Galactic]

This post (and the thread linked to by PH) has got me wondering whether a bar like a Jones H, the Ergotech Space bar or indeed the one in the photograph Jupestar has just posted could, in some situations, save the day (or at least the rider) in case of a break next to the stem? Anyone have any experience or thoughts?

PS Also had a bar break in this way on the second morning of a long tour (it was a Humpert Ally butterfly). Fortunately, it happened just as I was mounting, so no damage to me. And double plus good: a bike shop was just a few hundred yards away and I got there 20 mins before closing time so the tour was saved.

[gazza_d]

I've broken 3 pairs of handlebars over the decades.
First was some GB drop bars descending a French Alp in the early 90s which were about 5 yr old and had seen a lot of use with a handlebar bag
Then in 2018 and again in 2019 whilst commuting.
Both were flat bars. Both failed without warning and no specific root cause that I could fathom. The bars attached to the green bike with probably about 17 yr old, but the ones on the orange Moulton were only about 4 yr old.
I should add for the nervous that none of the failures resulted in injury and I was able to "crash" in a semi-controlled manner.

[peetee]

It’s not unusual for stems to have sharp edges that will score a set of bars if they are rotated. I notice from the photo in your first post that the outer surface of the bar nearest your arms and chest have failed right at the stem edge. My guess is the corresponding edge of the stem has scored the bars leading to a weak point and a crack which has propagated subject as it is to tension when loaded by yourself and braking forces.

[TrevA]

I had a set of Cinelli drop bars that snapped. They had a thicker collar where the stem was, that protruded about an inch each side. The bars snapped at the end of the collar. This was in the middle of a ride in the Peak District and I had to get a lift home. The bars were only about 4-5 years old.

[firedfromthecircus]

Thanks for the replies. As a couple of posters said I'm going with general fatigue on them.

Look at the areas on the stem where the anodising has worn away to silver. On one side there is a clear area right at the very edge of the stem clamp area. That looks suspect to me! YMMV.

[Barrowman]

The loss of paint 'inside' the clamp says not tight enough and some movement to me .
Wouldn't need to be much, but regularly over a long period would do it I fear.