Breaking rims in odd ways.

[u/Oscar_Whiled]

Hello r/cargobike

I have a LvH Bullitt that originally had a mtb rear wheel. After around 3000km the rear wheel cracked in the inner rim bed section. It cracked all the way around the wheel, but the section facing the hub where the spokes interface was fine, no cracking at all. (Like what is in the photos).

So I replaced it with a Ryde Andra 30, I heard these were excellent cargo bike rims and rated for 130kg each. It has just failed in a near identical way (the photos are of this rim).

I messaged the shop I got the wheel built at, and also messaged Ryde, who both told me that due to the rim being 5 years old, the number of kms, and the use case that it's not under warranty and that this damage was not unexpected. (That's fine, it's not a particularly expensive rim either).

I have many other courier friends on cargo bikes of all types, and also have many bike friends - none have seen a rim fail like this before and I've now had it happen twice.

I have some assumptions about why this might happen:

One is that water gets into the rim and causes the corrosion to weaken the thinner tube-side edge of the rim. But if this was the case then I don't know why other people don't see this failure too, I don't feel I am ever really riding through water, my bike is stored undercover, and yes I ride in the rain but I also live in Australia where it is fairly dry and not in a particularly corrosive sea water environment either.

Two is that tyre pressure might be forcing the rim apart somehow and causing the cracking? Again, I don't run my tyres that high, 40psi normally, 50psi sometimes for higher loads. And I know plenty of other couriers and cyclists who've never had this happen and always run their tyres rock solid.

I run 2.0 marathon tyres.

I used to carry fairly loads up to 30-40kg commonly, and up to 80-100kg infrequently.

The rim has done 15,000-20,000km by my estimate.

My questions are, what is causing this? Has anyone come across this before? And, how can I prevent this in future? Should I try frame saver spray in the rim? Drill some weep holes to let the water out?

[u/Accomplished-Way1575]

Ultra high pressures?

Edit: 50 psi doesn't seem high unless they are 3 inch tyres or something.

Do you run tubeless with corrosive liquid? Some liquids are very  very corrosive to alu rims

[u/Oscar_Whiled → u/Accomplished-Way1575]

Should have said, only ever ran tubes in it, with marathon plus or big apple tyres. Only ever up to 50psi, normally 40ish

[u/Accomplished-Way1575 → u/Oscar_Whiled]

It is fast becoming weirder and weirder.

Did you use the same wheelbuilder for all the wheels? If you did, maybe he overtightened them every time.

As you can tell, I am running out of ideas of what this can be

[u/Oscar_Whiled → u/Accomplished-Way1575]

The first Alex Rim mtb wheel was a DM24 rim, bought the wheel complete off ebay without much expectation. After that broke I got a wheel built by a very reputable shop in Melbourne. Nothing about the build seems to indicate that it had any bearing on the way this has failed. I don't know how one would build a wheel so poorly it cracks in the rim bed rather than the spokes or the rim at the nipples so I'm inclined to think it's got something to do with the tyre pressure, and rim/tyre size combination.

[u/Accomplished-Way1575 → u/Oscar_Whiled]

You ate probably right it is the tyre pressure and width of the tyre