it depends on many,many things.
track temp is the first variable. the higher the temp, the lower the pressure.
tyre type is another. a sports touring tyre will not get as hot as a super corsa, so will need more pressure in it as there will be less increase in internal gas pressure.
are you running 100% nitrogen or basic air (it's amazing the difference that 20% of oxygen makes)
however for supercorsas i run 26R and 30F and have a play in the 3rd session if the tyres look like they are cutting up.
for 023's i'd drop to 34F/R and move about from there, unless it's really cold.
