Why hozn might like rim brakes**

[hozn]

Yikes, my name in a thread subject !! I have clearly managed to be notorious on this topic

Though I am not sure I understand; is this a disc-brake wheel pictured? (Or are you saying that the brake pads alerted you to wheel being out of true?).

That looks bad, though! I have never pulled a spoke through the rim or broken a rim like that. Spokes, yes. Bent rims (on rocks, curbs), sure.

Is that right at the weld? Looks like a 32h or 36h rim? What kind of rim & how many miles?

[peterw_diy]

Brake pads alerted me. This is my original Mundo wheel. 13ga spokes, 48h, 14mm solid axle.

[peterw_diy]

Brake pads alerted me — I expect that if I had switched to a disc brake in the rear I would not have noticed this until it had become much worse.This is my original Mundo rear wheel. 13ga spokes, 48h, 26″ rim 30mm wide (outside), 14mm solid axle. Running big 2.0″ tires. The wheel probably has less than 1000 miles on it, as we may only use the bike for short distance trips. You can see tears by two spokes in that picture. There is a third tear on the opposite side of the wheel. I have been a pretty careful rider, but it is the cargo bike rear wheel, and I have had as much as 250 pounds on the rear, but it’s rated for 200kilos/440# so that should have been OK. Drive side spokes are rather tight — about 175 kgf and I have little doubt that contributed to the failure (all cracks are at drive side nipples). I’m wondering if the rebuild should use DT’s 13/14/15 Alpine III triple butted spokes, following the theory of butted being more elastic & reducing rim stress…

[hozn]

I’m guessing you would have felt the wheel squirreling out on you; I have when I break a spoke, but maybe not right away with such large tires. And since disc brakes are harder on the spokes/rims, the main difference might simply have been breaking something sooner. (Though that type of failure, as you point out, does sound like over tensioning.)

But that is a very young wheel and some pretty crazy high tension. 48h makes even more sense than thinking it was a 36; those spokes look awfully close together.

Maybe a Sapim Strong spoke (maybe that is equiv to the DT Alpine)? I have no experience building wheels for that type of load. It feels like the elastic is a good idea; I have had a couple 14/15 double-butted spokes break on disc-brake rims, but so great luck with the thinner Sapim D-light or DT Swiss Super Comp. (And great luck with Sapim CX-Ray.) The idea that the thinner spokes will stretch/compress more and keep wheel under tension seems like it would yield a stronger wheel, but I’m happy to admit that I have a pretty cursory understanding of the stresses at play on wheels.

[jabberwocky]

48h on a 26″ rim is crazy high. Thats a lot of holes through the rim. My understanding is that moving beyond 32 on a 26er rim started to compromise the rim strength just because the spokes are so close together; at that point you’re usually better just going to a heavier duty rim if you want more strength rather than throwing spokes at it.

175 kgf is awful high too. I’m not sure what spoke/rim they use on that wheel, but my MTB wheels are usually built to 115 or so, and I doubt adding spokes increases the required tension.

[peterw_diy]

@jabberwocky 114072 wrote:

my MTB wheels are usually built to 115 or so, and I doubt adding spokes increases the required tension.

Drive side or average? NDS here is about 110, as if they did the exact opposite of what Sheldon Brown suggests, and watched the NDS tension but ignored the DS tension.

Or maybe the rim is supposed to tolerate 175 — Park Tool lists some Bontrager rims speced for DS tension of 122-181 kgf.

I’m planning to have BicycleSpace rebuild with a Rhyno Lite, which Sun specs for 110 kgf max tension. And I’ve pinged Yuba to get their opinion. Hopefully they’ll be frank since I’ve basically acknowledged that the Mundo warranty only covers frame & fork.

[hozn]

115 average on DS is pretty typical (for mtb esp). Most of my rims are rated for more so I build to 130kgf or so and use nipple washers (though that doesn’t seem as though it would help here either).

Yeah, 110kgf for the NDS on a non-disc hub (wider flange spacing on NDS) is crazy; it almost does sound like someone was measuring the tension on the wrong side of the rim.

[jrenaut]

When carrying children, it’s hard to tell if the squirrelling is coming from the wheels or the cargo.

One of the main reasons we went with the Xytracycle over the Yuba was that they seemed to be built better. Though you have me planning to check my rear wheel more often – it’s mostly covered by the bags so it’s tougher to inspect.

[peterw_diy]

@hozn 114088 wrote:

110kgf for the NDS on a non-disc hub (wider flange spacing on NDS) is crazy; it almost does sound like someone was measuring the tension on the wrong side of the rim.

Actually it is a disc hub. Mundo ships with cheap V brakes (which have been totally fine with Kool Stop salmons), but fork, frame, and hubs are disc-ready.

@jrenaut 114090 wrote:

One of the main reasons we went with the Xytracycle over the Yuba was that they seemed to be built better. Though you have me planning to check my rear wheel more often – it’s mostly covered by the bags so it’s tougher to inspect.

Same problem here wrt inspection — top 60% of the rear wheel is covered with the black plastic wheelskirt. I’ve been meaning/hoping to use some salvaged plexiglass to make new, transparent skirts as I miss seeing the wheel. I’m a little worried the plexiglass skirt might end up looking too hillbilly, tho.

[dasgeh]

@peterw_diy 114117 wrote:

Same problem here wrt inspection — top 60% of the rear wheel is covered with the black plastic wheelskirt. I’ve been meaning/hoping to use some salvaged plexiglass to make new, transparent skirts as I miss seeing the wheel. I’m a little worried the plexiglass skirt might end up looking too hillbilly, tho.

Ooooh. I want a plexiglass skirt!

[dkel]

@dasgeh 114120 wrote:

Ooooh. I want a plexiglass skirt!

Really?? I thought you would have a bit more modesty than that…

[peterw_diy]

Followup: Yuba says 175kgf DS is about right(!!!), and this damage is rare. They offered me a deal on a replacement wheel and I’m going to give that a try, and maybe make those see-through hillbilly skirts that dkel is so worked up about…

[hozn]

That is quite amazing, but great that they offered a new wheel. Of course, if it is the same rim I am not sure I would trust it in the same context … Not like it was just a broken spoke.

But I hope to be wrong!

[peterw_diy]

@hozn 114243 wrote:

But I hope to be wrong!

Yep. They’ve sold enough of these bikes that I think there’s a reasonable chance that my first wheel was defective and the second will be OK. I hope so!

[peterw_diy]

I was clearing out the garage yesterday and pulled out this wheel. It’s been just sitting in the garage for the past three years, waiting for me to salvage the hub. Check out how much worse those cracks are!

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