i switched from 16" rims and tires to 17" rims and tires on my 04 V70... i am running 34psi right now and some times i still hear the tires squeal a little bit. so should i try more or less air.
Chalk the outer edge of the sidewall (up to the outer edge of the tread) and go out and do some "sporting" cornering. If any of the chalk wears off the sidewalls you need to up the tire pressure a bit.
stopped by a tire dealer ship and asked them. he told me to stick with the cars recommend tpi on the gas door.... which for my V70 is 32 up front and 30 in back. still getting some squealing around corners with that too.... maybe its my alignment??? i have since changed front struts and left driveshaft, and outter tie rod ends are on the way.
you can check the all important details on your tiers there is a sidewall on your tiers which contains a set of letters and numbers of the form AAA/BBC-DD EEEF, where AAA = section width, BB = aspect ratio, C = construction, DD = wheel diameter, EEE = load index, and F = speed rating.