Using XT cassete with OneUp 40t + Zee FR rear derailleur.
Is chain too short or just right?

Depends how much chain growth you have under compression

I bust 2 mechs and a hanger with that combination

no chain growth – rigid bike 😉

Looks a little stretched tbh. Did you follow the guide on OneUp’s website? I think it tells you to add 4 links as opposed to the 2 you normally would when wrapping the chain over the 40t and your front chain ring but not through the rear derailleur.

This is the old chain, was surprised that it works.
Will add 1 link (inner + outer) when I fit the new chain just to be sure.

Fine on a rigid / HT in my opinion / experience

Could try an extra link but would depend on how slack it was.

One full link more. Better?

I’d say so. The new clutch type mechs don’t clatter anywhere near as much and hence using chain length to keep tension is less of an issue now.

The new clutch type mechs don’t clatter anywhere near as much and hence using chain length to keep tension is less of an issue now.

hmm not quite, I’ve seen a number of setups, incl my own, that set it up without putting it through the gear mech. and following the instructions and online guides. the results were excessive slack on the smallest gear (pic 2 above). after ditching the how 2’s and just going by eye we all ended up with less links in the chain. no amount of “clutch” will take up that amount of slack. do like the these clutch’s though.