Jim – yeah, that was basically my thoughts, there’s only quite a small weld area onto the chainstay, the weld that’s capping the tube won’t take any of the stress because the cap is so thin. I did some guestimate calcs on the shear stress on the chainstay/seat stay welds and they didn’t come out high enough to be a problem if it was not a weld, but at the weld then there are always gonna be faults. Yes I’m quite sad and consider these things too much.
This is different to the steel ones I’ve seen where the plate is bent over and forms the end caps on the stays, which strikes me as a much more robust joint.
That said there’s quite a few out there that haven’t broken, but I have a feeling it’d be less if that weld area was bigger. The stays on the other side don’t have to react any torque (apart from any drag from the hub which is pretty negligible), so it’s bound to break on the brake side first unless there’s a massive manufacturing defect on the drive side.
My thoughts on stresses in HT vs FS are that probably the HT takes more of a pounding for a given speed as the peak forces will be higher, average forces (i.e. how fast you can stop on a rough surface) don’t matter. Worse for fatigue also as the forces are applied and removed more often. It’s probably pretty negligible thouggh as the maximum force is dictated by what the rider can hold on to more than anything else!