Rim hairline cracks - bin.....failure mode?

[hoogerbooger]

Just noticed these and quite a few more hairline cracks on a "MT19 Hard" 559 36h rim from rear of touring bike. Off to Netherlands on tour next week so I'll swap in the old wheel with somewhat worn rim......

I'm presuming the failure mode on a rim with such hairline cracks and full panniers could be sudden??

I'm rather surprised and dissappointed in the rim. It's not done big mileage and mostly not touring . It's one of two NOS rims I bought....the other not yet made into a wheel. It's double eyeletted and I'd bought specifically intending them for rear wheels. Many of the cracks are nowhere near thes spokes/ eyelets, which is where I've seen cracks develop in some Mavic rims used on the rear of our tourers..but they wre mainly radial rather than lateral. They don't seem to be just surface scratches. Pretty obvious if you drag a finger nail over them.....but seems strange when well away from spokes?

[Barrowman]

Right not to trust it I would say ,interesting the wear track has plenty of depth in it . Mavic used to be top drawer , MA 40 , MA 2 last forever . I do have a NOS Mavic Touring Rim ( not sure which model) if it helps at all, West Midlands based. Are you considering complaining ?

[geocycle]

Are these cracks or scratches? Look very regular to me.

[531colin]

What’s the finish?
It looks like some sort of a coating or paint, rather than anodising.
The “cracks” aren’t straight if I zoom it, do the cracks wiggle where the paint thickness changes?

[cycle tramp]

Um.... when did you last stare at your wheel rim and can you remember seeing them, then?

[Brucey]

they do look like cracks to me,sadly. You are quite right, they are in a funny place though. I would hazard a guess that they are indicative of faulty manufacture in some way. The majority of the rim is in compression; but locally, the spoke tension loads may be shared by the two walls/double eyelet.

[hoogerbooger]

There has definitely been a few for a year or so. (Some did LEJOG). Whilst I have cleaned that bike more often than the Mrs since then....I put my glasses on this time!! for the pre-tour service.

Originally, when there weren't many, I thought they could be scratches. But there are loads now and all are lateral and none off-line at an angle. A few more photos for those interested, attached.

I fear Brucey's view is probably the most likely.....and so I should presume the other rim is from the same batch and will do the same if used.

(So, this type of cracking is not from particular points of stress ( e.g.) at spokes.....but essentially brittle metal and the effect of constant contraction/ flexing in line with the wheel??)

They are DRC "MT19 Hard" rims ( bought from SJS in 2019). Discontinued for some time now....from my now limited bunker of silver 36h 559 oldskool braked rims. I had presumed they were hard anodized, but can't find anything on the Web.

On mode of failure.......I presume it is more risky on the front than the back. But I'm tempted to use the other rim on the front as a non touring wheel, and inspect it regularly, as the front would have less load and, if lucky may not start to crack.

[Brucey]

that the cracks (if indeed that is really what they are) are not straight in that particular way is highly suggestive of intergranular cracking. The most common cause of this if solute partition from the melt. I'm not quite sure what to look out for in Al alloys, but in steel similar behaviour is caused by high levels of S and P. However, in materials which protect themselves from further corrosion via an oxide film, such as stainless steels, Ti alloys, and Al alloys, a different mechanism can operate. In this, the oxide film is at its most defective (and the material most vulnerable) near the grain boundaries. This can make the material very vulnerable to SCC.
The good news is that it seems unlikely that a rim cracked in this way would fail catastrophically, and on the front it will see less road salt and you will be able to keep an eye on it. FWIW I'd expect the wheel to go badly out of true in the death throes.

[cyclop]

Sorry,why chance it....just bin it.

[hoogerbooger]

Thanks Brucey. I like to know stuff....and don't like not knowing.....has left me metalurgically curious. I am minded to destruction test on my own bike ...but not on tour....so won't bin yet.

I've just been to the bunker to do a head count of spare rims. The unused rim has one location with similar cracks/marks !

[mig]

i don't that that they would bother me too much....at the moment.

i'd ride them, clean them, inspect them - especially if they are not regularly subjected to large loads, fierce braking etc

[Brucey]

....The unused rim has one location with similar cracks/marks !

more evidence that this is indeed a manufacturing fault, I would say.

[cycle tramp]

....The unused rim has one location with similar cracks/marks !

more evidence that this is indeed a manufacturing fault, I would say.

....yeah - however is this the case where the coating has simply cooled too fast ?- Pulling back from the metal of the rim and by doing so casing 'cracks' to appear in the finish, without affecting the structure of the rim....
(Think of gravy being left to harden on a plate for 3 days- as it dries, it will pull back from itself leaving cracks).
..the only way (and it may hurt if the rim does have structural issues) is to put a little spot of orange paint at the end of each crack and see if any more cracks appear or the cracks continue to grow - if either or both happens, there's an on going issue and you should probably stop using those rims..m

[rogerzilla]

I think I have several rims like that. I don't think.it's anything to worry about, as those cracks aren't going to.open up. The sort of cracks to worry anout are circumferential (e.g. where braking has worn the rim thin) or radial around the spoke holes, which could indicate imminent pull-through.

[Brucey]

I think I have several rims like that. I don't think.it's anything to worry about, as those cracks aren't going to.open up. The sort of cracks to worry anout are circumferential (e.g. where braking has worn the rim thin) or radial around the spoke holes, which could indicate imminent pull-through.

I agree, but 'no cracks' is always infinitely preferable to 'some cracks'.......