Hard Anodized Rims - is it structural?
 

OK, so here is a shaggy dog story about hard anodized rims. The bike in question has a history.

The bike came with Campy hubs, Mavic Open 4 hard-anodized rims, and Hoshi blade spokes.

https://cimg4.ibsrv.net/gimg/bikefor...1c137947e8.jpg

Two spokes on the rear wheel had been replaced with regular spokes when I bought it, and the spokes just kept breaking, even after I had the wheel re-tensioned at a local bike shop (one that employs mostly grown-ups rather than high school kids). I figured the problem was the weird spokes, so I asked to have it rebuilt with all new spokes. The guy declined to do it because he said the rim did not have the strength to be rebuilt.

I did not really understand his explanation, so I took the wheel to another bike shop for a second opinion. Another fully grown-up employee told me that when these old hard-anodized rims start losing the anodized layer on the brake tracks, it affects the strength of the wheel. Well, something is certainly affecting the strength of the wheel, because it keeps going out of round and breaking spokes. So I got lucky and found a set of wheels with slightly later Campy hubs and Matrix rims to ride for now. But the Matrix rims are the same hard-anodized finish, so I guess I need to know more about 1980s hard-anodized rims.

I spent some time looking at old threads here, and I see a lot of information about the spoke holes giving way on old hard-anodized rims, but I do not see anything about worn brake tracks being a structural problem. Does anybody have thoughts on this?

You may have seen this: https://www.sheldonbrown.com/brandt/anodized-rims.html

I can understand the shops did not want to rebuild a wheel using used parts, especially with that history of spoke breakage.

But hard anodizing leading to microcracking and subsequent structural failure of the rim? Nah! If nothing else, there'd be too many law suits.

Also, aluminum oxide is not a bad thermal conductor. Combined with the thinness of the layer and it integral coupling to the underlying aluminum,... Nah! Not a problem. You'd have to show me a thermal analysis or test data to get me to believe otherwise.

What hard anodizing does, if it does anything, is provide a HARD, more wear resistant, surface for the brake pads to bear on.

I'm going to go and look up the coefficients of friction for aluminum and aluminum oxide. That will be interesting.

The thermal conductivity coefficients should be close to those, have a look and think again; values vary, of course, but figures quoted in the papers I scanned are around 30-50 W/mK for the oxide, and 5 to 10 times that for unanodized extrusions.

Those are plenty strong, it could be the shop thinks your old wheels are a rabbit hole.

I have thought that when spokes break it usually means uneven tensions per givin side. Rims that have some damage can have spokes tweaked loose and torqued. Always on the rear, I've never broken a spoke on the front (knocking wood for future).

There are some hubs that are known to prone to breaking, the Maillard Helicomatic is famous for problems. I think they had more dish than others back in the day.

Al2O3 is definitely lower than Al, no doubt there.

My point is, as oxides go, it is one of the better ones (more conductive). That it is so thin also mitigates any significant impact on temperature rise and heat dissipation.

Remember also, bare aluminum immediately corrodes and grows an oxide layer (admittedly thin).

I went looking but did not find any coefficient of friction values,... yet. :-(

All the above is secondary to the sanity check - I've never heard people say anodized rims are dangerous or braking performance is reduced due to overheating. If either were true, that product would be withdrawn from the market. Did that happen and I just missed it?

Some of the crap people get told by bike shops…..wow….

Both bike shops employ pretty good people. I think the guys I talked to just saw more downside than upside in building that wheel.

So does anybody want to speculate what's going on with that back rim? Each time it got trued up it spun pretty straight until the spokes started breaking. No visible damage (aside from the brake wear) and no bad potholes or other extraordinary incidents to cause the broken spokes.

Or is it just the way of the C&V warrior that I have to learn to rebuild the wheel myself?

A lot goes into wheel building and using different types of spokes will affect tension balance. Having recently built a few sets of wheels (and being someone who wants to know everything beforehand in order to do it right) I referenced https://spokecalc.io/spoke-tension-t...tive-guide.php as well as the Park Tools videos. I think that rebuilding used anodized wheels is fine but you should source new matching spokes to ensure the correct tension balance. Also check the spoke holes on the hubs since these can wear out and cause problems. Learning to build them yourself is a great excuse to purchase a tensioner that will provide insight to potential future broken spokes and give you the assurance of getting far from home knowing that you will make it back without trouble.

have we discussed spoke tension yet?
Inadequate spoke tension is an effective way to fatigue spokes. Typically, the spokes will fail at the head.

Steve in Peoria
(and have we discussed how hard it is to know the correct tension? ... especially for those of us who refuse to buy a tension gauge)

The rims should simply be built with new butted spokes. Shop rat opinions and analyzing what's wrong with them is likely futile.
We restore or rebuild vintage bikes so take any shops opinion with a grain of salt unless they really buy into vintage rides..

yeah, any civilized person would build with butted spokes. A little more cost, but a much better wheel.

Steve in Peoria

Those rims look hardly worn to me. Spokes are just fatigued. Rebuild with butted spokes, and give them a good stress-relieving. :thumb:

OK, thanks everyone, the spokes seemed reasonably tensioned when I bought the bike, but maybe it had been ridden with insufficient tension in the past and the rear spokes were all just waiting to fail. Two had already been replaced before I came along.

I guess this will be my first wheel building project.

Buy top quality spokes & brass nipples, the best-fitting spoke wrench you can find and get a tensioning gage. The gages are not all that much and worth the peace of mind they will give you.

Get a truing stand, too, either DIY or used.

Sheldon Brown's instructions are as good as any on how to do this.

It is actually easy and satisfying. Take your time.

This from JB (R.I.P.) via rec.bicycles.tech:

"From the FAQ:
-----------------------------------------------------------------------

Subject: 8.18 Anodized vs. Non-anodized Rims
From: Jobst Brandt <jbr.. @HPL.hp.com>

There are several kinds of dark coatings sold on rims. Each suggests
that added strength is achieved by this surface treatment while in
fact no useful effects other than aesthetic results are achieved. The
colored rims just cost more as do the cosmetically anodized ones. The
hard anodized rims do not get stronger even though they have a hard
crust. The anodized crust is brittle and porous and crazes around
spoke holes when the sockets are riveted into the rim. These cracks
grow and ultimately cause break-outs if the wheel is subjected to
moderate loads over time.

There is substantial data on this and shops like Wheelsmith, that
build many wheels, can tell you that for instance, no MA-2 rims have
cracked while MA-40 rims fail often. These are otherwise identical
rims.

Hard anodizing is also a thermal and electrical insulator. Because
heat is generated in the brake pads and not the rim, braking energy
must cross the interface to be dissipated in the rim. Anodizing,
although relatively thin, impedes this heat transfer and reduces
braking efficiency by overheating the brake pad surfaces.
Fortunately, in wet weather, road grit wears off the sidewall
anodizing and leaves a messy looking rim with better braking.

Anodizing has nothing to do with heat treatment and does not
strengthen rims. To make up for that, it costs more."

Markets are as rational as manufacturers are ethical.

@albrt - Where did the spoke fail?

WRT rim failure, based on the quote, failure would happen around the riveted sockets. Has anyone seen this type of failure? I have seen failed sockets due to corrosion but not the rim.

note the bladed spoke notation- do those spokes require the enlarging of the hub spoke holes? I have not used that brand.

otherwise a "true" wheel can be created from a problem rim, that uneven tension will continue to be an issue.

I have seen failure on a well used rim at the transition to the sides, the whole inside surface erupted. Not common.

The spokes are hook-end like these:

https://cimg2.ibsrv.net/gimg/bikefor...d798d03f09.jpg

They all broke at the hub, same place normal spokes break. The hubs do not look like they were drilled out or otherwise damaged.

Bad batch of spokes? Poorly built? Suffice to say they won't do.

Ah, okay cracking at the spoke holes. I thought we were talking about cracking on the braking surface.

A minor technical point/correction - heat is generated at the interface between the brake pad and the rim. This is where the frictional force is created and that is the source of the heat. That is why I was looking for coefficients of friction for bare and anodized aluminum. If one wants to "worry" about heat conduction during braking, concern yourself with the thick rubber brake pad.

Nonetheless, thanks much for that blurb.

As an aside, I ride on 37 year old MA-2's.

If spoke tension is too high, or too low, the wheel will probably be fine for a while. More than once I've built up a wheel and got it perfectly true and dished, and it rode fine for about 400 miles... and then spokes started popping. It's metal fatigue, and it affects all of the spokes. They all have to be replaced.
I've built a lot of wheels, and I've always had an unprofessional attitude about it, so i have rarely used a spoke tension gauge. I've been punished for this, and the punishment was i had to rebuild the wheel with all new spokes.
I've built a lot of wheels on dodgy old rims, another thing a professional would never do. If the rim isn't perfectly straight and round, spoke tension will never be even, but you can still build a perfectly good wheel. It's a pain in the ass but you can do it. That's why the bike shop won't touch it (and maybe liability issues).
The "hard anodized" rims I've encounteted were also heat treated. I don't know exactly what that means, but in my experience those rims are a harder and stiffer material than regular aluminum alloys, and they will crack where other aluminum would bend.

These are probably the type of spokes that Sheldon Brown is referring to in his Wheelbuilding article. He doesn't give too much detail. Excerpt below.

There was a fad in the early '90s for Hoshi "blades" which had a double bend instead of a conventional head. The double bend allowed the spokes to be inserted "head first" into the hub flange, so that they could be used with normal hubs. Unfortunately, they turned out to be prone to breakage, and I can't recommend them.

Thanks, that's good to hear. This bike was probably re-done by the original owner right in that early 90s time frame. If the spokes are bad then it's less likely there is something fundamentally wrong with the rim.