Overtensioned spokes?

[robjh]

I've just put a new Mavic Open Pro C (700c, 32 hole) rim on a front wheel to replace an older buckled one, reusing the same hub and spokes.
I've done this before (on other wheels) using Open Pros a few times with no great problems.

I got the wheel pretty much true and round to my satisfaction, but then noticed faint marks on the rim on either side of some eyelets that turned out to be slight deformations, or raised areas, in the surface.
They are just about visible as white areas to the R and L of the eyelet in this photo:

My first thought was that I'd seriously overtensioned the spokes, so I loosened everything off by half a turn and retrued the wheel, which wasn't hard.

The spokes don't feel exceptionally tight to the touch now - there is some give in them if I grab neighbouring pairs - and the ping tone is not crazily high to my ear, but I have no tension meter to prove anything definitively.

So my questions are more or less:
- is this rim damage caused by over-tight spokes?
- can I do anything about it now it's happened?
- should I worry?

Thanks for any thoughts on this.

 

[Yellow Saddle]

No, no and no.

 

[robjh]

No, no and no.

I like your answer.

Any idea though what those deformations around the eyelets are? They certainly look like some kind of stress damage in the rim surface.

 

[Yellow Saddle]

I like your answer.

Any idea though what those deformations around the eyelets are? They certainly look like some kind of stress damage in the rim surface.

Those deformation are deformations. Put your left hand flat on the desk. Now pinch some skin from just behind your knuckles using the fingers from your right hand. Pull a teat. That's exactly what's happening with the rim. It is a thin aluminium skin resisting about 100kg of tension and of course it deforms.
The little cracks you see on there are called crazing and is an artifact of the anodising on the rim. That rim is anodised. Anodising is a super-thin layer of ceramic that lies one half on top of the rim and one half inside the aluminium of the rim. Note the difference between paint and anodising. Anodising penetrates, paint layers. Anyway, because anodising is coloured ceramic, you can imagine that it doesn't bend very well, it simply cracks. That's what you see.
So, yes, it is some form of stress damage, but it is harmless in the short term. Long-term, on an item with cyclical stresses like a rim, it eventually leads to rim failure around the spoke hole. You'll see plenty of people here call it "spoke pull-out" or "spoke pulled through" or such. In reality, the spokes didn't pull through the rim but the rim collapsed around the spoke.

If you still have your hand on the desk pulling teats in your skin, vary the pull by pulling harder and softer. You'll see the deformation grow and shrink, grow and shrink. That's what happens when a wheel rotates. Each time a spoke reaches the bottom of the wheel, the teat relaxes, only to be pulled out again as soon as the spoke rolls away from the load zone above the road.
Those cyclical stresses make the anodising crazing grow deeper and deeper and eventually right through the rim. Had the rim been painted, instead of anodised, only the paint would crack, but it isn't, it is anodised.

Anodising stress is best visualised with a very scabbed knee. Imagine you went skateboarding and did a stop from high speed by skidding on your knees like John Travolta in whatever that movie was called. Your knee will be scabbed over. Wait a few days until the scab is nice and hard and now suddenly bend your knee. Ouch! The cracks in the scab penetrated whatever skin remained and went right down to the nerves.

Although that's a mode of failure for anodised rims, there's no need to panic. Most rims die from other natural causes long before being killed by anodising. These causes are typically, in this country, brake track erosion. That's another story.
Go for a ride, drink a beer.

 

[robjh]

Those deformation are deformations. Put your left hand flat on the desk. Now pinch some skin from just behind your knuckles using the fingers from your right hand. Pull a teat. That's exactly what's happening with the rim. It is a thin aluminium skin resisting about 100kg of tension and of course it deforms.
The little cracks you see on there are called crazing and is an artifact of the anodising on the rim. That rim is anodised. Anodising is a super-thin layer of ceramic that lies one half on top of the rim and one half inside the aluminium of the rim. Note the difference between paint and anodising. Anodising penetrates, paint layers. Anyway, because anodising is coloured ceramic, you can imagine that it doesn't bend very well, it simply cracks. That's what you see.
So, yes, it is some form of stress damage, but it is harmless in the short term. Long-term, on an item with cyclical stresses like a rim, it eventually leads to rim failure around the spoke hole. You'll see plenty of people here call it "spoke pull-out" or "spoke pulled through" or such. In reality, the spokes didn't pull through the rim but the rim collapsed around the spoke.

If you still have your hand on the desk pulling teats in your skin, vary the pull by pulling harder and softer. You'll see the deformation grow and shrink, grow and shrink. That's what happens when a wheel rotates. Each time a spoke reaches the bottom of the wheel, the teat relaxes, only to be pulled out again as soon as the spoke rolls away from the load zone above the road.
Those cyclical stresses make the anodising crazing grow deeper and deeper and eventually right through the rim. Had the rim been painted, instead of anodised, only the paint would crack, but it isn't, it is anodised.

Anodising stress is best visualised with a very scabbed knee. Imagine you went skateboarding and did a stop from high speed by skidding on your knees like John Travolta in whatever that movie was called. Your knee will be scabbed over. Wait a few days until the scab is nice and hard and now suddenly bend your knee. Ouch! The cracks in the scab penetrated whatever skin remained and went right down to the nerves.

Although that's the mode of failure for anodised rims, there's no need to panic. Most rims die from other natural causes long before being killed by anodising. These causes are typically, in this country, brake track erosion. That's another story.
Go for a ride, drink a beer.

Thanks, that's a very informative reply.

I've used Open Pro rims for years, and they typically fail on the braking surfaces after a fairly predictable amount of usage. I expect that will eventually be the case with this one too long before it gives any problems around the spoke holes.

 

[Ajax Bay]

My last Open Pro rim (on the rear) developed cracks around the spoke holes with plenty of life (thickness) left in the braking surfaces. I think the relative wear/fatique race depends on the type of road (eg rural/urban and typical soil/road detritus type) and the rider's approach to braking.

 

[rogerzilla]

Black anodised rims often lose the anodising (to be replaced with white powdery corrosion) around the spoke holes after a few winters. FWIW, I ran the same DT XR 4.1 ceramic rim (negligible rim wear) for 7 years' commuting and the spokes never pulled through, although it looked slightly ropey. Someone else has that wheel now.

 

[silva]

Problem location related: had a rim with outer walls' circumference showing a crack crossing the spokes holes, leaving the inner wall alone to hold the rim together.
A suggested cause was a tyre pressure (though still well under the tyres' max) that the rim could not handle.
A solution was given as a rim replacement by a brand/model whose spoke holes were punched instead of the drilled ones of the cracked one.
An explanation was given as that drilling creates a rougher hole edge than punching (= cold forging - strenghtening?) does, facilitating initiation/growth of cracks.

 

[rogerzilla]

To be honest, there are good rims and bad rims and you can't tell which are which except by people's experience over thousands of miles. Some double eyeletted (socketed) rims can crack. Some rms with no eyelets at all can survive until they wear out. Cheap rims can outlast expensive rims. Rim manufacturers don't always know what makes a good rim either - Mavic is just a marketing operation these days.