So WTF happened?

[frankenthorn]

Back on the 18th August what was otherwise a pleasant cycle into work was suddenly disturbed by my bike becoming uncontrollable, followed by my coming to on the road in a lot of pain.  Fortunately a pair of my colleagues (and a random white-van-man) came upon the scene, and a lift into work for me and my bike was provided.  However it quickly became apparent that this wasn't a case of "Ow!  That hurt!" but something rather more serious and a 999 call ensued!  ENTONOX is a wonderful thing, and a rapid trip through Aberdeen Royal Infirmary revealed a fractured collarbone, a nice blow to the side of the head and possibly 2 broken ribs.

I've just been down to work to examine my bicycle and the front wheel is in an interesting state, to put it mildly!  https://photos.app.goo.gl/n12lCNLHVYvm67Ri2  So now I'm trying to work out what happened, because I'm leaning towards the theory that the wheel rim has failed at the joint?  And I don't think that should've happened to a wheel that's 13 months old and only actually been used for about 8 months?

I just thought I'd see what the assembled wisdom was here before I write a rather stroppy email to the online retailer who built & sold that wheel to me!

(In other news, recumbent trikes are seeming much more appealing!)

[guidon]

Definite failure at the rim joint, weld??? What brand of rim was it?? Hazard a guess at Mavic as they make wheels in Romania....However get well soon!!

[frankenthorn]

Definite failure at the rim joint, weld??? What brand of rim was it?? Hazard a guess at Mavic as they make wheels in Romania....However get well soon!!

Yeah, it was a Mavic ...  And yeah, I guess failure of the weld is what I meant.

Am improving, can now use my right arm for some things!

[mrcharly-YHT]

Looks like  a pinned rim to me. I think the pin failed and a spoke pulled through - maybe the spoke went first.

[frankenthorn]

Looks like  a pinned rim to me. I think the pin failed and a spoke pulled through - maybe the spoke went first.

The spoke in question is a little over 90 degrees away from the rim failure, though whether that signifies anything I wouldn't know.

[Kim]

Presumably some normally inconsequential event caused extra stress that lead to the failure happening at that particular moment.  Perhaps one of those killer pebbles that had me off in May, or similar.  The tyre appears to be in decent condition, is the tube still inflated?

[frankenthorn]

Presumably some normally inconsequential event caused extra stress that lead to the failure happening at that particular moment.  Perhaps one of those killer pebbles that had me off in May, or similar.  The tyre appears to be in decent condition, is the tube still inflated?

Yeah, I was rather surprised to note that the tyre pressure seemed entirely normal for a bike that's not been near a pump for almost a month.

[Kim]

Thinking about it, it was probably the end of the rim snagging on the brakes that had you off the bike.  I can imagine that would have put some fairly nasty stress on the spokes...

[hubner]

Might  the crash be caused by the bent rim getting caught in the forks, making you go over the bars?

It's a guess, maybe the spoke tension is too high and something set the rim off to go "pringle" shaped, and the joint being the weak point opened up. Maybe the very  narrow hub flanges had something to do with it.

[Samuel D]

Hazard a guess at Mavic as they make wheels in Romania....

You present this sentence as if there were some logic to it, but I’m only parsing tabloid racism. What am I missing?

[frankenthorn]

Might  the crash be caused by the bent rim getting caught in the forks, making you go over the bars?

What little I can remember of events has things being like when you try to stop pedalling on a fixie and the bike tries to throw you off?  I thought I'd almost caught it, and then discovered I hadn't!

Thinking about it, it was probably the end of the rim snagging on the brakes that had you off the bike.  I can imagine that would have put some fairly nasty stress on the spokes...

It would fit with loss of some control, followed by Sir Isaac Newton taking over for me ...  I suspect trying to ride a rim like that, even if wasn't rubbing/catching on anything would be an "interesting" experience but if catching (without totally jamming) then every ~2m or so I'd have something causing a rapid piece of braking which certainly wouldn't help things like stability and control.

[Cudzoziemiec]

Hazard a guess at Mavic as they make wheels in Romania....

You present this sentence as if there were some logic to it, but I’m only parsing tabloid racism. What am I missing?

Made in Romania is clearly visible on the rim.

[Samuel D]

Made in Romania is clearly visible on the rim.

Ah! Thank you. That entirely changes the meaning of guidon’s remark. Sorry for leaping to that baseless accusation, guidon.

Let the investigation proceed.

[rogerzilla]

Mavics are crap these days.  All marketing, no substance.

[Randy_Butternubs]

Alternative theory - is it possible you had some kind of tank-slapper causing the wheel to turn sideways and buckle under the force? Or the wheel could have been damaged in the crash by some other way rather than being the cause of it? I ask because Roger Musson claims that spoke tension alone should hold a wheel together strongly:

"The rim in a fully tensioned wheel is subjected to a high compression force and to illustrate this I built a wheel from a rim sawn into pieces which were initially held together with tape [...] I completed that build and the fully tensioned wheel was a solid structure and with the wheel flat on the ground it could easily withstand my full weight on the edges of the rim." - Roger Musson, Professional Guide to Wheel Building

Edit: Your description that the bike became uncontrollable and was trying to throw you off sounds a lot like a tank-slapper to me. I'm not sure if there's an equivalent bicycle term.

Edit 2:
Here's a vid showing  a mild version of the effect: https://www.youtube.com/watch?v=xODNzyUbIHo
I couldn't find a severe one on a bicycle but this shows it well on a motorbike: https://www.youtube.com/watch?v=I71Y2PfCuy8

[rogerzilla]

It's quite possible that the rim buckled under compression if there was a manufacturing weakness in the joint - slightly misaligned or machined too thinly.

[Sergeant Pluck]

How was the wheel built, 2 or 3 cross? I wonder if it is related to the large flange hub, consequent more extreme spoke angles at the rim, and excessive spoke tension in some spokes.

Edited to add: this thread might get more replies if moved to The Knowledge, where the people that know what they are talking about hang out.

[aidan.f]

Those SP hubs are narrow and have low bracing angles which will compound any other weakness due to poor wheel build.

[Greenbank]

How thin are the walls of the rim? (Do you have a set of calipers to measure that?)

If there was excessive rim wear (from rim braking in those 8 months) it's possible you could have worn the brake track enough that it failed at the join (then got snagged on the brake block and caused the off, which may have caused the subsequent spoke damage).

[Rod Marton]

It sounds very much like the rim failing at the joint - this has happened to me once. Fortunately I was not on the bike at the time but mending a p******e, the pressure of the tyre lever on the rim was sufficient to spring the joint. Admittedly the lever was close to the joint, and the load on it was not typical of cycling, but it still shouldn't do that and I was aghast to think that I had just been touring on that wheel. After it had sprung out there was no way I was going to try riding on it, but the rim would certainly have caught on the brake blocks and stopped the wheel rotating. This sounds very much like what happened to you.

For information the rim was a bit worn but not excessively, and it was also a Mavic rim. There are clearly faulty rims out there.

[Asterix, the former Gaul.]

Mavics are crap these days.  All marketing, no substance.

My 2000 tourer started life with Mavics which proved to have a very short life due to rim wear.  Maybe I was lucky to survive?  Conversely my Open Pro rims have done very well (built by Harry Rowland).  I have been using better brake blocks these days, the early ones ISTR were Shimano's.

[Brucey]

it is very difficult to establish cause and effect here;  did something funny happen and cause a prang that bent the wheel, or did the wheel start to collapse for some reason and did that cause the accident?

I've seen a lot of pranged wheels  and they very often bend at a pinned joint during the wheel failure. I have never seen a wheel that failed 'because of the pinned joint'.

However the wheel may be the culprit in this case. The latest mavic CXP rims are made in Romania. They look like the older CXP 22 rims but they are not the same. They have heavily machined braking surfaces (which are piss-thin just like all the other mavic rims are these days)  and are slightly lighter. Some old model CXP22s had thick braking surfaces and an external wear indicator. These rims last for ages, if they don't crack first...

All wheels are (in theory) vulnerable to a self-pringling failure mode. It is really a sort of Euler buckling; an elastically initiated instability that, during failure, may become plastic (i.e. permanent). If you read a good wheelbuilding book (Like Brandts) it will explain this in more detail. Most modern rims are not as vulnerable to this kind of failure as they used to be; when Brandt wrote his book most rims were. He used the onset of self-pringling as a proxy for setting maximum spoke tension. There is a whole generation of folk who build wheels that have never seen this happen. Current CXP rims (and other similar) can self-pringle.

Things that make this likely to happen include

- a rim that isn't very stiff
- a rim that isn't very strong
- a wheel that has uneven tensions
- a wheel that has very high tensions
- a wheel that is heavily dished
- a wheel that has narrow-spaced flanges
- a wheel that sees a lateral force

It is impossible to say what happened exactly, but I will note that some wheelbuilders refuse to build certain rims onto hubs that are built like that, with narrow spaced flanges, because when the spoke tensions are as high as they like them to be, the wheel is on the verge of euler buckling.

Hope you are healing OK.

cheers