Alexrims DH19 (pics attached)

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Chris Clode
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Re: Alexrims DH19 (pics attached)

Post by Chris Clode »

I had the same rims on my Ridegback voyage. After about 3000 miles I wore through the wear indicator on the back wheel. This was using it for about 20 months on a 20 mile commute in all weathers 9a lot of it wet in South Wales), with at least half of the journey on a canal path. I think I probably wore about 3 sets of brake blocks out in that time.

Now I do ride over some pretty severe pot holes etc which are unavoidable on certain sections and I do kerb hop, but my rims were still good apart from the rim wear. I'm fairly lightweight ( about 11 stone) and only carry a change of cloths and perhaps a packed lunch.

I would agree with most of the other posts that your rims were faulty.
stoobs
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Re: Alexrims DH19 (pics attached)

Post by stoobs »

531colin wrote:If this bike is really less than 12 months old, the wheels are a disgrace. Take it back and get it fixed or replaced under warranty.
Sales of goods act, fitness for purpose, etc etc.
The photos show clearly the rim cracking next to the spoke holes, a typical fatigue failure. Touring rims have no business failing like this, if they are up to the job the typical failure mode of touring rims is the brake blocks wear through the sidewalls (eventually), which is fair wear and tear.

Edit- picture shows failure at every second spoke....I bet these are the driveside spokes, which are under more tension (=more fatigue) than the others

Edit edit -Unless you weigh 20 stone, of course.


Despite the bike experience of 531colin, I find this conclusion to be a little premature (sorry, Colin). And in addition to your comment about spoke tension being a red herring.

I'd like to see exactly how many eyelets this has happened to, which side (and I suspect that they are drive side, as does 531colin), and whether the cracking is on both sides. More tension as such does not necessarily equate to more fatigue. The average load and the amplitude of the variation are both factors. I'd also like to see the hub flanges to see whether there;s any failure there.

Fatigue tends to highlight other problems. The Comet crashes are a good example. The planes crashed after fatigue failure. The cabin compression/decompression was the facilitator, but it was the combination of square windows (tight radius at the corners which raised stress substantially locally) and the entrance hole for the vhf antenna, which caused the propagation of cracks from poorly machined rivet holes around the windows.

Relevance here? Well, there could have been defects caused by extrusion of the rim under the wrong conditions (think how play-doh gets surface cracks when extruded). The wheel could have undergone a one-time major impact which initiated cracks which then grew (hence my query about how widespread the pattern is). And, which I would only guess from the limited picture posted, severely over-tensioned spokes which would explain why it looks as though not only has the rim cracked, but it looks to have done so on both sides, and pulled inwards from the "normal" shape. Fatigue is only a secondary factor after the root cause in this scenario. It highlights the weakness induced by other things.
stoobs
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Re: Alexrims DH19 (pics attached)

Post by stoobs »

Interesting, too, that the drawing on the website does not match the photo above it, but your rim matches the drawing cross-section (at least externally). Changes in thickness/profile/cross-section can also raise stresses and concentrate failures in specific areas.
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531colin
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Re: Alexrims DH19 (pics attached)

Post by 531colin »

Well, I know nothing about Comets, and actually being neither engineer nor metallurgist I dont know much about fatigue either, perhaps I shouldn't have used the word.

What I do know is this type of failure is typical of light rims, the brand name begins with "M" and they are generally very "in your face" on the Tour De France on the telly. The eyelets pulling through only ever involves a handful of eyelets. Perhaps they are all initiated by damage from potholes or whatever. In which case the rims are still unfit for purpose, if that purpose is touring. When you get a lot of cracking around an eyelet, of course it pulls in. What else could happen?

Spoke failure at the elbows is generally attributed to fatigue, and they dont all fail at once, it is a "death of a thousand cuts" as odd spokes fail over months. It would be quite exciting if all the driveside spokes failed at once!


Can we agree that UNDER THE CONDITIONS OF A BIKE REAR WHEEL more tension = more fatigue? I know as you say, the fatigue is caused by fluctuating load ( rotating). However its my understanding that you need to approach "yield point" in order to get fatigue? I build rear wheels to a tension of 120Kgf for the driveside and 80Kgf for the other side, so I don't see how you could approach yield point on the non drive side, the drive side would all have broken long since. I dont accept that that the affected spokes were necessarily grossly over tight, they may have been at the top of the inevitable slight variation, or they may simply be in a bit of the rim that is thinner or has some imperceptible manufacturing fault or variation. Pothole damage usually creates an area of slack spokes, not tight spokes, as the rim is deformed towards the hub.
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CREPELLO
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Re: Alexrims DH19 (pics attached)

Post by CREPELLO »

I think the point that stoobs has made is a good one - I thought the same as well. The rim profile seems flawed in that it introduces an unnecessary stress riser along that line between spokes and rim. It seems so unnecessary and yet it may well be the flaw that created the fatigue. A well designed rim would hold those spokes well without fatigue.

I wonder whether that rim is single or double eyeletted?
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squeaker
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Re: Alexrims DH19 (pics attached)

Post by squeaker »

531colin wrote:However its my understanding that you need to approach "yield point" in order to get fatigue?
'Fraid not, at least as far as aluminium and its alloys are concerned. It has a finite fatigue life, whatever the cyclic load, but if designed correctly, that life will be 'inifnite' as far as the owner is concerned.
More here.
HTH
"42"
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531colin
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Re: Alexrims DH19 (pics attached)

Post by 531colin »

squeaker wrote:
531colin wrote:However its my understanding that you need to approach "yield point" in order to get fatigue?
'Fraid not, at least as far as aluminium and its alloys are concerned. It has a finite fatigue life, whatever the cyclic load, but if designed correctly, that life will be 'inifnite' as far as the owner is concerned.
More here.
HTH



All lost on me, I'm afraid. Anybody do a children's version?
stoobs
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Re: Alexrims DH19 (pics attached)

Post by stoobs »

I need some time to think about this, because you raise some very interesting points.

Just to clarify on fatigue life, (and hopefully this qualifies as a simpler version as requested!) components don't have to be near yield point in order fail by fatigue from the varying loads. The finite thingy just means that below a certain level of varying stress, steel components will never fail. For aluminium, there is no lower stress level at which fatigue will cease. As such, aluminium components effectively have to be designed so that they will survive a large number of cycles with cracks growing - on the order of tens of millions - in order to last longer than the user.
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531colin
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Re: Alexrims DH19 (pics attached)

Post by 531colin »

stoobs wrote:
Just to clarify on fatigue life, (and hopefully this qualifies as a simpler version as requested!) components don't have to be near yield point in order fail by fatigue from the varying loads. The finite thingy just means that below a certain level of varying stress, steel components will never fail. For aluminium, there is no lower stress level at which fatigue will cease. As such, aluminium components effectively have to be designed so that they will survive a large number of cycles with cracks growing - on the order of tens of millions - in order to last longer than the user.



Make it even easier for me?
Fatigue will happen quicker in bits of the rim under high stress (anchoring driveside spokes) than in bits under low stress (anchoring non- driveside spokes)....TRUE OR FALSE?

Sorry, I'm not being belligerant, I just don't know. I used to be able to learn fast, and now I can't, and thats not a good feeling! I half remember something called micro-yielding, do you get more of that closer to the yield point, or only with greater variations in load? I 'm not really sure what I'm asking........I think I would have to be content with a one word answer to my true or false above .
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squeaker
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Re: Alexrims DH19 (pics attached)

Post by squeaker »

531colin wrote:Make it even easier for me?
Fatigue will happen quicker in bits of the rim under high stress (anchoring driveside spokes) than in bits under low stress (anchoring non- driveside spokes)....TRUE OR FALSE?

TRUE: for the same number of stress cycles (load on / off) provided that the stresses are higher under the drive side spokes (e.g. the rim section might be asymmetric to cope with higher drive side spoke tension).
"42"
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531colin
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Re: Alexrims DH19 (pics attached)

Post by 531colin »

Thank you!
thirdcrank
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Re: Alexrims DH19 (pics attached)

Post by thirdcrank »

It seems to me that we have a range of possible causes and it would be useful to know what's at the bottom of this.

Unsuitable use? Manufacturer's description suggests it's intended for this sort of use.
Abuse? OP says not.

That leaves things that are in the hands of the rim manufacturer and the wheel builder (in this case almost certainly a machine with perhaps human finishing.)

Inherently poor rim design? That's been suggested above.

A fault in a single rim or a batch? We know about two now. What surprises me about 531colin's find is that it was just that. I should have assumed - obviously mistakenly - that if a rim that had failed like that had been brought into a bike shop, the gasps of amazement would have been heard streets away, yet if he had not been researching for this thread, it sounds as though that rim would have gone to the great scrapyard in the sky unremarked. In which case, there may be more of these elsewhere which have been taken for granted.

Poor wheelbuilding? The pattern of damage makes it look as though the spoke tension has pulled the rim apart, but I should have thought that would be impossible. Perhaps not.

This probably says something about the way the modern cycle trade operates. There may be so many bikes sold that never really get ridden very far. Perhaps the typical wheel is buckled, upgraded or whatever before this type of failure is noticeable.

Does it matter? Bearing in mind the relatively low mileage reported here, if you bought a bike new in January, used it regularly and then attempted the End-to-End, you could have a shot rim after the first couple of days. :shock:
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NukeThemAll
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Re: Alexrims DH19 (pics attached)

Post by NukeThemAll »

I experienced exactly the same fracture pattern on a set of Alex rims - on my son's bike which was a competition prize and extremely lightly used for the first 4 years (we're talking < 30 mins on the road) quite literally whilst the bike was stored in the shed. I contacted Alex, they agreed that there had been a faulty batch, and they sent me some new rims all the way from Taiwan (if I recall). Still cost me to get the new wheels made up, since both front and rear had cracked. These were disc rims, so can't blame rim brakes.
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531colin
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Re: Alexrims DH19 (pics attached)

Post by 531colin »

Ooooh look..........Twins!!

Image

Image

Image

Image

The 2 eyelets that have pulled in are cracked both sides - photos from both sides.

A total of 16 eyelets show cracking to some degree - 2 fuzzy photos each of 2 eyelets with cracking.(white line)

1 eyelet is cracked both sides but not pulled in - in a different part of the wheel to the 2 pulled in.

So 13 eyelets cracked 1 side only.

Cracking involves alternate spokes, so I guess driveside.

I maintain this is fatigue due to poor rim design/construction.
cvaughan
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Re: Alexrims DH19 (pics attached)

Post by cvaughan »

Just for an update.. took the bike back to Pedals Cycle Centre where I brought it...

They were shocked about the way the wheels had gone wrong so quickly and offered to replace them without question. Their supplier couldn't supply the same rim as instead I now have Mavic A319 rims front and back...

I'll let you know how these ones fair...
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