Carbon-Ti is responsive. A calliper resulted that the shim is 0.28 mm, which is slightly compressed according to Carbon-Ti (They said the tolerance is 0.3~0.4 mm).
Here is how to set preload given by Carbon-Ti, if anyone need to adjust the preload:
"First you need to know that the bearing preload of the rear hub closes the play by turning counterclockwise, opens the play clockwise.
Now we recommend first of all to open the bearing preload clockwise (unscrewed the grub screw), then check that the axle end is closed using two good quality 5 mm hex wrenches.
Then tap the inner axle of the hub sideways on the side of the freewheel with a plastic hammer to put the axle end in good contact with the outer bearing of the freewheel.
Then close the play with the bearing preload by tightening it counterclockwise with your fingers only (no tools required) until it stops. From that position lighten clockwise a quarter turn to relieve the pressure in the bearings. Finally close the grub screw fixing the bearing preload."
They also confirmed that my hub has a new-designed rubber seal with a lip, which is different from the one in the manual online.
Though the first time I follow the suggestions step by step didn't improve the freewheeling much, I find that the hub needs a break-in, due to the new rubber seal.
After 80 km soft ride, back spinning the crank can only move the wheel slightly now. It's still not ideal and the drag in the freehub is a bit high, but much less concerning now.
alanyu wrote: ↑Sat Jun 04, 2022 7:53 pm
However, there is freewheeling problem. The wheel spined backwards when I back spinned the cranks. I disassembled the hub, and shockingly there is only one 0.1 mm shim between the bearings. It should be one 0.4 mm or 3 * 0.1 mm in the old design. I have no idea whether it is due to QC of carbon ti, or due to the builder not puting all shims back. I have written to them, but they both are in holiday atm.