I check the max psi/load rating on the sidewall, and then go with about 80-90% of that. SO if the tires are 44 max psi, then 36-40psi.
By the way, tires generate heat because of sidewall flex, so the higher the pressure, the LESS they heat up. That's why those Firestones were blowing, they were too LOW and they overheated.
Low pressures will not give you better traction. You need those sipes and grooves held wide open to get a good grip on the slippery surface. So again, a higher pressure will give you more traction, (only if you are in deep sand will you need to let air out, and I mean to like 5psi!).
--
744 & 745 16v 4+OD, 245 SE auto, 242Ti 4+OD, 245DL auto parts car

Above 40 psi is HIGH because when you drive it heats up and Pressure goes up.

Also High P can create less friction because the part thast "touches" the road is central with peripheral part of the tires now "off ground":

The picture to the far left explains this situation.

http://www.procarcare.com/images/shar/encyclopedia/8852OG17.gif

I have used Gislaved for years at 35-36 psi (cold measurement) and have had good wear and good traction.

cn

Using my gauge - I run 42/38 psi COLD from the garage - good traction, good wear pattern - stable 140km/h+ Toronto, Canada

MAT

32-36...depending on your comfort level.
--
1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.