The generalizations I made came from my experiences playing around with different gussets and butts. Its a bigger picture conclusion rather than individual analysis
The picture I just showed was:
- TT: 28.6-969,
- DT: 38.1-969
- Gusset: .9 thk
I think the long butt should definitely be placed at the HT end. The real-world failures and FEA support this. When I said the butt location and length were unremarkable, I was referring to two tubes that had the same butts, but slightly different butt lengths (ie. Tange vs Zona DT). The 50-100mm difference in the butt lengths had minimal impact on the stiffness of the frame.
In comparison, going from a .5 to a .7 butt has a much bigger impact.
This gusset is modeled as if were perfectly attached to the tube. I think this is testing the best-case scenario. In the real world, there would be stress concentration and HAZ from welding.
That is a good point. I feel like the gusset discussion is very similar to the Willis brake mount failues. Adding more material to spread out the load makes sense in theory, but in reality, it could just be adding stress risers, more HAZ, or relocating the force to a thinner part of the tube.
Without real-world test data, it would be hard to definitively answer the gusset question. But at best, the FEA says it’s a minor improvement.