[Closed] Dtswiss 1900 rear failure 😞

In the absence of further information I'd put my money on the bolts being loose-fatigue-failure.

Sounds like the bolts failed not the wheel itself.

When this happens it usually because 1 or more bolts has worked loose, meaning that the braking load is shared between fewer bolts and eventually something has to give as the remaining bolts are overloaded.

So long as the bolts are loc-tited and torqued to spec it's vanishingly rare for this to happen so I'm guessing whoever installed your rotor may not have one or either of these things.

4 out of the six hub bolt mounts sheared

Do you mean the part of the hub the disc mounts to has somehow come away from the rest of the hub shell? If so, that's a pretty crazy failure. Pics?

If you just mean that the disc pulled itself off the hub and removed threads as it did so, I'm calling mechanic error as above.

Threads have been ripped out and 3 of the six mountings have snapped edges

Almost certainly the bolts were loose, you can generally get away with only three if they're tightened properly

I'm going with overtightened.

We are just taking calculated guesses but I am going with the loose bolts theory.

I often see bikes that have slightly loose rotor bolts. Not so much that there is any rattling or side to side play coming from the rotor, but apply the brake firmly and rock the bike forwards / backwards and you will see the hub moving but the rotor stays aligned with the caliper.
Upon braking, the bolts, and in turn the hub shell are subjected to side loading which they are not designed to handle. This happens hundreds of times every ride, and aluminumium fatigues when repeatedly stressed (i.e. aluminum commuter bikes cracking at the seat tube / BB welds due to constant flexing).

Or it could be Covid.

Brexit, definitely

I think loose bolts too, I had the same with my first ever discs 20ish years ago, a hope hub had got down to two bolts due to me not having tightened them properly. One ripped out of the disc mount eventually, took a chunk out of the bulge with the thread in and killed the ride. Still used the hub for years after with 5 well tightened and threadlocked bolts.

Looking at the new DT Swiss 350 hubs (2021 model I think) there has been a lot more material removed from those bolt mounts in comparison to the previous model. I think they did the same to an even greater extent to the latest 240 hubs too. Hope Pro4 hubs have about 2mm extra material at the top of the bolt mounts but the same (~10mm) at the bottom of the bolt mounts as the 350 hubs.

In an effort to save weight the tolerances to user error are slightly less forgiving with the DT Swiss hubs. I don't know what model of DT Swiss hub you have, I'm almost certain it's neither of those, but if DT Swiss have applied the same weight saving changes to your hub then that too will be less tolerant of loose bolts which would cause vibrations and twisting forces leading to catastrophic failure. Cold weather would make aluminium more brittle too I should have thought although I'm no materials expert.

Hang on!

6 bolt rear hub or 6 bolt rotor and adaptor on centrelock hub?

@RAGGATIP DT rotor mounts have offset drilling so there’s more material supporting the load under braking and less in the other direction as it’s not needed for normal braking and so a sensible area to gram count. If you ride fakie a lot, and brake riding backwards, it’s not a great solution for you.

Anyway - OP - under tightened bolts.