Dymag carbon wheels

[andygtt]

Lucky, You seen this?

I cant beleive this happened without an impact but well worth asking them direct!

[LuckyP]

Another reason not to run slicks!!

[KETZER]

Wow! Sure would like to read the story behind that failure?

I think it bears noting, the carbon didn't shatter, splinter, crack, explode, or any of that other crap the naysayers say it will do.

[UltimaCH]

Too much torque and sticky slicks perhaps??

[andygtt]

it was a GT3 aparently!

[LuckyP]

Why only one spoke has broken off at the hub and all others broken half way along? The damage to the face of that one spoke looks a bit suspect too???

[GreenV8S]

From the name I guess the spokes were magnesium, which is notorious for fatigue failures. This hub design would result in relatively high deflections in the spokes (since they're effectively only supported at the inner end) so will be particularly vulnerable to fatigue and I wouldn't be surprised if the wheel had just been used beyond it's life.

Edited by GreenV8S on Tuesday 23 December 15:07

[suntiger1965]

Looking at the photo i can only wonder how the spokes are bonded to the carbon wheel??

Are they just stuck on? Thats a very small surface area of bonding.

I would imagine a recess for the spokes to sit on before bonding but looking at the photo i can not see that. Surely thats the way of 'not' ripping the spokes off under acceleration??? and i presume there is a HP max. they will withstand?

And yes magnesium does have a relative short shelf life.. The race team used to change all the marchenisi and Dymag wheels every season(never understood why as id have loved a set for my bike) due to stress cracking..

Any time limit advised when you bought them Lucky??

[GTR-TT]

LuckyP said:

Another reason not to run slicks!!

I'm pretty sure those are hoosier R-tires, not slicks.

[deadscoob]

Where was the image from?

[LuckyP]

suntiger1965 said:

Looking at the photo i can only wonder how the spokes are bonded to the carbon wheel??

Are they just stuck on? Thats a very small surface area of bonding.

I would imagine a recess for the spokes to sit on before bonding but looking at the photo i can not see that. Surely thats the way of 'not' ripping the spokes off under acceleration??? and i presume there is a HP max. they will withstand?

And yes magnesium does have a relative short shelf life.. The race team used to change all the marchenisi and Dymag wheels every season(never understood why as id have loved a set for my bike) due to stress cracking..

Any time limit advised when you bought them Lucky??

Spokes are bolted not bonded.

HTH

No idea of life? Whoops.

[deadscoob]

Probably longer than an AS engine?.....

[bluesatin]

What is wrong with AS engines-mine still going nicely after 8 years!

[Davi]

LuckyP said:

Spokes are bolted not bonded.

But in a very bad way IMO - the bolt effectively becomes a pivot point for the spokes in the same plane as the torque is going to try and turn them.

[deadscoob]

Perhaps you should apply to Dymag for a job then as you know better than them

[Davi]

deadscoob said:

Perhaps you should apply to Dymag for a job then as you know better than them

You say that as though the fact they are a large company makes them immune from stupid mistakes or poor design? Suppose that means no manufacturer has ever had to do a recall for a potentially fatal design flaw?

[deadscoob]

No. I say that as a photo of a broken wheel has been posted and people are making comments and judgements without any facts to back them up.

[GreenV8S]

Davi said:

LuckyP said:

Spokes are bolted not bonded.

But in a very bad way IMO - the bolt effectively becomes a pivot point for the spokes in the same plane as the torque is going to try and turn them.

It's bad from that point of view, but a simple bolt is never going to have enough stiffness to do any good anyway. This way at least ensures that the spokes and the rim aren't preloaded so they fight against each other. It looks as if the bolt is some way off the neutral axis of the spoke though and if so that's bad news.

[LuckyP]

Davi said:

LuckyP said:

Spokes are bolted not bonded.

But in a very bad way IMO - the bolt effectively becomes a pivot point for the spokes in the same plane as the torque is going to try and turn them.

I'm struggling to understand this comment - please help.

Take hold of a pen in your right hand. With the thumb and forefinger of the left hand take hold of the tip. Now as you describe pivot point, that is like trying to turn the pen using the righthand around the held left hand end - very easy - but if you only apply a force perpendicularly to the left hand then the pen bends - that is how the force is transferred to the rim. The bolt is no pivot - only a fixing.

How are you explaining it?

Pete

[edfoxuk]

there is no strength at the rim/spoke junction that is why it failed.

The spokes rotated at the hub and without any real bracing/buttressing at the rim it destroyed itself. The problem is the jointing of two materials in an area of the wheel normally offering structural rigidity.

the fact that the cf isn't damaged is academic, it didn't do any work and probably rolled off on its own down the road,