100 kPa = 14.5 PSI

for my iswara, i pump 235 kPa front and 190~200 kPa rear for best FC. a bit bouncy lah, but got shiok lighter feeling and better throttle response. and when pumping above the recommended pressure, even if u forget to pump for a while, the pressure is still near or above the recommended level. if u pump ngam-ngam at the recommended level, when u forget to pump for some time it'll be way below it.

i know of a friend driving an iswara a/b who pumps 250 kPa for all 4 15" tyres

30 psi sounds low for a normal street-driven car, probably dragging the engine a bit too. u can try higher pressures bit by bit till u find a best compromise that makes the car lighter yet not too bumpy

40 psi is still within the limits of most tyres, but the more you pump, the closer it is to this limit, and therefore there's less safety margin to work with if the tyre hits a big hole or object on the road. just my 2 cents