I’m making a chunky tyre belt drive commuter/bikepacking bike where the customer would like an integrated rear rack which is able to click in a Tailfin top bag (Cargopack/Aeropack etc).
I was looking to integrate the alloy top plate from their Journey rack, with a 4130 arch and then a connection to the seat cluster. Customer likes the look of continuing the top tube straight line so was proposing brazing on a stub here. Would be about 75mm before it joins to the rack.
Aesthetics aside (although open to improvements that keep the principle!) do you think this will hold up? Currently proposing 12dia 4130 arch and 16dia stub ~0.9mm wall.
Will be stipulating the same Tailfin weight limitations (10kg on-road / 5kg off-road). Connection of the stub to the rack obviously needs to be stiff/rigid to minimise it peeling the brazed joint at the seat tube. Where it’s nestled in-between the top of the seat stays may also help with this?
Seems reasonable. Is the rack aluminum? Will you put a binder on the stub? How far will rack insert into the stub?. You could brace the stub against the seatstays .
The Tailfin top frame is aluminium. I would machine & TIG a plug for the end of the 4130 stub that then attaches to the frame the same way as their stock connectors (slides inside, pulled in by main bolt and then locked by a traverse bolt - see below). Thought about adding either a brace down to the seat tube, or pair to the seat stays but already looks very busy in the area.
Alternative would be to try and make the whole rack in steel, but thought it would be easier to integrate the pre-made part which guarantees the fit/interface with the bag etc.
Seems reasonable. In terms of busy looking, I’d prefer that over broken. a couple small braces wouldn’t be out of place. The weight is well forward of the rear stays so it’s all sitting on the stub and attachment point.
There will be a lot of torque around the stub where it attaches to the ST, so I would definitely add something to triangulate it and support some of the vertical load.
OTOH, you could use a thinish plate to give it some vertical compliance, but that might look odd.
