Handlebar failure likely cause?

[Dingdong]

I'm wondering if carbon handlebars aren't much safer. They have much more tensile strength then aluminium, and they can take a tremendous amount of repetitive stress in the direction they are designed for. I have one piece Carbon bars on my best days bike and they seem extremely rugged.

Aluminium has a tensile strength of 40 KSI (276 MPA)

Carbon fibre in laminate form has a tensile strength of 600 MPA.

[Jupestar]

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

Photo 1: handlebar positioned so stem would be on the left. Handlebar clamp face on the right.

Photo 2: stem on the right, clamp on the left.

For what it's worth. I think the top bolts were tightened more than the bottom bolts. Although all came out easily. The top of the handlebar cracked as a result and eventually the bar gave way down to the bottom


At the bottom you can just make out the final break where it snapped there is a bit of a bend.



you can see in the photo below. There is a discolouration Between the clamp area and the bar area. You can see it clearly on the non-broken side. On the brokenside alot of the break is clean on this line.. that is also at the top where the too stem bolts were. In this photo you are looking down at the handle bar.

I don't think the stem cut or scored it. I can't see anything on the stem to suggest it, and the anodising is fairly uniform rubbed off. Possibly but I think the top clmap.bolts were two tight.

[Jupestar]

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.

Possible as they came out quite easily, but never noticed the brake levers dropping down.

The first photo I posted, you can see hardly any gap at the top of the stem, and much more at the bottom. Suggest uneven loading. Possibly not tight enough...

[pwa]

Things you can do to reduce the chance of this happening again:

1) Take a piece of emery paper (or any metal sanding paper) and smooth away anything on the edge of the clamp that might scratch a bar.

2) Make sure you don't overtighten the clamp on the replacement bar. And do the bolts fairly evenly.

3) Buy from a known brand.

4) If a bar becomes significantly scratched, especially in an area close to the clamp, stop using it.

[cycle tramp]

Way back in 2017 I wrote that I would never use alloy handlebars and I've still not done so.

Looking into the spheres of motorcycling and bmx handlebars (where the stresses to tge handlebars are much higher and any failure more likely to result in life changing injuries or death) I now wonder if we've got the design of the bicycle handlebar completely wrong.

Neither bmx or motorcycle handlebars have a bulge formed in the middle for clamping purposes. Motorcycles and bmx 'bars are completely smooth which, to me, indicates that the formation of this bulge for bicycle use weakens metal in that area of the handlebars, even before it is used.

The reason for this bulge is to increase the diameter of the bars to allow greater clamping forces to be used to stop any handlebars from twisting in the stem, even when fully tightened.

I now see this as failure of the bicycle stem itself. Going back to motorcycles and bmxs, their handlebars do not twist in their fittings when used, despite having no bugle and being subject to higher stresses.

This is due to the handlebar clamping area being spread wider across the handlebar because the clamp is much wider than that of the nominal bicycle stem.

The way forward would be to produce handlebars with no bugle and produce stems which are have a much wider clamping area, or a y-shaped stem where the bars are clamped in to separate areas, and there by reducing the damaging leverage of flexing handlebars.

For the moment in heavy use applications I would advise steel bmx handlebars mated with a bmx stem to avoid handlebar breakage.
Whether you can find a bmx stem at the right length to go with the bmx handlebar of the right height and sweep, I can not say.

[Jupestar]

In short for heavy use applications I would advise steel bmx handlebars mated with a bmx stem to avoid handlebar breakage.

I was thinking along similar lines to this post. Regarding the shape causing a weak spot. The ones I put on are steel, and they don't have this raised clamping area - although they do have a substantial shim - they In General feel much sturdier.... Shorter stem too. They are super wide I guess like 750mm, which gives the little one on the crossbar more space.. but even though they are wide they have this MX style bracing bar.

I was riding my commuter - which I recently put on a new set of drops (zipp service course - only 9.99 at CRC). Apart from constantly thinking about them snapping. I was also aware at what seemed like much less weight being forced on them. - checked the stem on this one with 2 different tourque wrenches...

[Biospace]

I saw a bike on the Tissington trail a few years ago with failure in exactly the same place, it was a bar with the bulge in the centre. It's very possible there's a localised concentration of stress with some designs at points just outside of the bulge when the bars are flexed. I might find a bike with a similar setup and try a failure test.

[PH]

Since my bars snapped I've decided to replace those on my two most used bikes every four years and on the lesser used folder every six. I'm also removing and checking as part of the annual service. I don't know how long it was between initial crack and complete failure, but I'm hoping a visual check will show up any potential issues. I've been moving over to Ergotec bars, who test and rate from 1 to 6, mine are 6!, though I've recently noticed a 6+ which I'll use in future. All my bikes are now flat bars, though that's unrelated. Undoubtedly OTT, but I'm keen not to repeat the experience and it seems a small cost for some reassurance.

[Maimu9]

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 .

[tenbikes]

^^^^^^ this.

Look at how much stress bars get in downhill mountain bike racing, especially these days. It's insane even allowing for suspension easing the load a bit.

Probably not a steel bar on the circuit, a few carbon but mostly alloy.

All with a centre bulge. All expensive.

Probably the odd failure there too to be fair but I'm betting crash damage plays a huge role.

Some cheap bars are just , well cheap and nasty.

[Jamesh]

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 .

Probably more likely poor metallagy as anything - cheap alloy which is hydroformed so is thinner where the clamp area is.

This leads to the likeihood of denting aka coke canning...

[tim-b]

IMHO you're probably all correct

Possibly but I think the top clmap.bolts were two tight

What I wanted to add was that the halves of the stem clamp will often have an equal spacing top and bottom (some don't, so RTM)
I set mine up using a very light torque and a 2-3mm drill bit alternating to set the gaps. When the stem bolts reach finger-tight then a final torque, still using a spiral pattern.
A touch of suitable grease in the stem clamp works for me, although others prefer to dry-fit. I've seen handlebars that have snapped on a turbo-trainer, which was almost certainly due to sweat

[Jupestar]

I've heard of handlebar rotting on the turbo due to salt. The amount I sweat would be a big risk for me if it's true. So I throw a towel over my cockpit.

For what it's worth the bike which the bars snapped on is far better with the 'new' handlebars now. Much easier for me to manage with the child seat. With the small stem is much more solid as well.

[531colin]

Just looking at this further to a recent question........to me it looks like they have manufactured in a perfect "stress-raiser" where the knurled bit of bar meets the plain bit......exactly where the failure happened!