I think 230KPA = 33 PSI is OK already
Especially yours is low profile tyre = harder.

Depends la if you want comfort. If you want to save fuel, go higher pressure slightly, say 250KPA.

I am using 35psi = 240KPA for my front tyres stock 175/70 R13. Feels just right, and tyres doesn't bulge out much.
Original manufacturer suggests 220 but I feel thats too low.