do the PSI change if I change the tire brand or model?
Short answer is NO. Always set pressures according to the owners manual, which for the R3 is 29PSI (200kPa) front and 36PSI (250kPa) rear. Pressures are the same for all load conditions, right up to the maximum load of 353 lbs. (160kg).
NOTE: the above does not apply to racing the R3. For racing
most people recommend 28psi to 30psi on the front tire and 30-32psi at the rear.
The reasoning for this is: the lower the pressure, the more the tire will deform at speed – deformation creates more friction between the tire and the track which in turns generates heat. And the more heat (up to a point) the more grip you’ll have. Lowering tire pressures also creates a larger contact patch, which means more rubber in contact with the track and hence again more grip.