does the 853 inbred take a different collar size from the regular beast? the one I've got of another inbred seems to need over tightening to keep the seat up.
It should take a 29.8/30mm collar as with the standard Inbred. I also noticed that I needed to over-tighten my collar (the jaws of the clamp seemed much closer together than on the standard Inbred) and queried this. I'm guessing, but I think that the 853 seattube is thinner walled than the standard DN6 one.
I've a salsa clamp on my 853. I use carbon paste on all my seat tubes now to avoid over tightening. Finish line do one for about £7 a tube.
29.8 with a Thomson post on mine. it's never slipped and I'm heavy...
reckon it's just a slightly duff collar then. I'll have a swap about and see if another offers more grip. thanks.