Rim cracks
 

I built wheels for our tandem using Ryde Andra 35 rims, 36 Saprim butted spokes, and Saprim polyax nipples. Sadly….After 7000 miles, much of which was heavily loaded, 4 of the spoke holes in the rear wheel have developed 5 mm long hairline cracks in the rim (not easy to see or photograph). The spokes are not next to each other, but in very different parts. The wheel remains perfectly true with average tension of 105 kgf (both sides, Rohloff) with 15% variation.

The cracks are very fine and I wonder if these are just superficial cracks in the anodized surface coating, is that possible? If not superficial, I am surprised since the rims are stout. Should I have used nipple washers? I suppose it is not worth the time to save the rim by adding nipple washers after the fact. Thanks for your comments in advance.

SAPIM...no 'r'. The rims are most likely toast but your lack of photos doesn't help.

No even the slightest deformation around the cracks ?

no r, got it. I was able to get this pic. There are 4 of the same size.

https://cimg2.ibsrv.net/gimg/bikefor...5be4fad2b8.png

Interesting... good question. Looking across the planar surface of the rim, across the crack, not even a slight deformation of the surface.

Then i would suggest loosening very slightly those nipples (not enough to change the truing) and hope they won't get any worse. :hug:

I don't know if it's any help, but here's a shot of my wife's Bontrager rear rim cracked after five years of gentle riding. She was riding this w/o incident on the rear wheel until a shop spotted it and we replaced it with Mavic. There were maybe ten cracks, this was the worst of the bunch. From a single bike.


https://cimg0.ibsrv.net/gimg/bikefor...5378970dd.jpeg

And a pic across the surface of the crack.
https://cimg5.ibsrv.net/gimg/bikefor...eca359d288.png

a cracks a crack, no pic necessary, especially on a hardened anodized rim. plan for a replacement. not sure if washers would have helped or not. but usually, it is either overloading, or overtension. i never did really like the hardened anodizing either. personal experience i have seen alot of cracks in rims that did that, way more than a painted or polished rim.

Al anodizing is harder and thus less flexible then the underlying Al rim. So it will generally crack before the base material does. But the qualifier is "before". In time the crack in the ano will be the stress riser for the base Al to start that crack at. Once a rim crack starts it's only time before that spoke hole won't support the nipple. Andy

Thanks, so perhaps I can mitigate the problem by backing off 1/8 or 1/4 turn on all spokes?

Just how loaded is “heavily loaded?”

I’ll defer to folks who have experience with that rim and similar cracks. My $.02 is the cracks in the anodizing may not necessarily be a precurssor to failure of the rim.

Those are such heavy rims. Did the rim have to go through severe a re-truing some time in it’s early miles?

Well if ya don't replace it you certainly should check it more than frequently. Really looks like an area of potential dangerous failure..

Quit goofing around.
just toss it.

will you really be comfortable riding it ever again!

Barry

Disappointing for such a beefy rim! :(

If the rim should be replaced, I'm not sure what would be much better for this to not happen again. The rim is one of the strongest on the market, but apparently not sufficiently strong for two people and their camping gear, etc. And so my question regarding nipple washers. I should have used washers.

Or maybe 15% variation is simply too much, and you should be aiming for less next time ?

Actually IME spoke pull throughs are relatively non incident related/causing. Having seen dozens over the years and many (maybe most) were not even noticed by the rider till we pointed them out. Often during a annual servicing of their bike. And we do ask if there's any issues with the bike they know of that we need to focus on at the time of the service ticket write up. The usual early indications (other then the obvious visual) are a rim that won't stay true. Andy

Yep. When I've broken a spoke on 32h wheels (it's happened a few times over the years), I usually figure it out because the rim rubs on the brake pad a bit, so I look to see what's wrong. Never had a catastrophic failure.

Back off the tension and keep an eye on it.
You have caught it early so it's not a problem for now.
You can judge its development over time.
I would say you have plenty of time to figure out something.

Thanks. Yes, figure something out. Backing off on tension seems prudent. I should have used washers, perhaps rebuilding and adding washer now would be good. I have 2mm thread on back side of nipples, so perhaps enough thread to add washers.

If you're going to take the time to rebuild it, I'd probably get a fresh rim to try with the washers. (That is, if you can find one.)

I've built lots of wheels with used rims (most of unknown provenance), but I figure anything that already has a sign of cracking will set me up for disappointment sooner rather than later.

^^^ Ya, explain to your stoker you are at the weight limit for that rim... 180 kilos....that the rim has cracks in it but you rebuilt it and it should hold for awhile.
I'd get a new hub... more spokes than 36....new rim, new spokes.

I had an Open Pro hard anodized rim that developed cracks like yours. I rode for thousands of miles and eventually replaced it with an Open Sport rim that was a little heavier and stronger. No problems.

Yes, perhaps, not trying to be argumentative. The rims are rated for (each) 130kg and tension 140kgf. Our total weight (w/bike and gear) is 210kg and tension is 105kgf, both well below max rim rating. It is a symmetric wheel so all 36 spokes are bearing the burden.