yeah, the lower the pressure the more traction, on any tire, but the lower you go the more risk of bottming and denting a rim as well as cutting a tire with the rim. different tires can allow lower pressures than others, you just gotta experiment like Blakchawk says.

For example, the radials like the ohtsu and the dunlop on the raptor (not the same as the banshee dunlop btw) sag more than non-radials with the same prssure and they also bottom easier and can't really handle anything lower than 5psi for the sake of bottoming resistance in rocky terrain. But beefier tires with much stiffer sidewalls can handle a little lower pressure, and lower pressures they need for a bigger footprint and better traction. The surtraks are a very hard and durable rubber and do not respond to pressure changes as much as the MX style tires. Another similiar example of this is the blackwaters - they are so hard that they will run and almost appear inflated with zero air.

I actually adjust my tire pressures for the place I'm riding, every ride, just like my shock settings.
Lower pressures will not wear a tire sooner, but on the contrary, more ground contact makes it easier on each lug because more lugs are on the ground, and less spin due to more traction means even less wear.

 

When I had my Z400 I ran 3.5 PSI in the rear tires all the time, year round. I never had a problem and they worked great. Going to throw my pro wedges on my V-Force and I think they will work great.

 

I know this isn't directly relevent to your thread, but it is an interesting tire story. We went riding at the Watersmeet, MI ride/rally last Saturday. Put on 185 miles. One of the guys has a lifted 500 Cat with 28" Outlaws. He blew out his left rear 30 miles INTO the ride. Rode it flat the rest of the day. Mostly 45mph cruising on abandoned rail grades and at least 25 miles on blacktop. That Outlaw lasted the whole day! Never came off the bead and no damage other than the original puncture!

 

The outlaw tire is the extreme, they are very thick and solid. I once popped off the valve stem on my front left tire and rode it home. Got a new valve stem on there and it worked great afterwards. I also rode on a flat rear for a weekend. All these big 6 ply mud tires will work with zero air pressure, they will just look square and loose alot of height.

The outsu is the other extreme, any sport quad tire is the other extreme, once flat you are done for. Just wanted to back up the outlaws some, they are a great tire.

 

The stock kendas do suck in every terrain , excepy ice w/ studs . The rubber is so hard they won't flex and they hold the stud super tight. I have 2000 studs in mine and I can honestly say I have not lost 1 single stud ! I also have the 12 oz of slime in each one also w/ no vibration at all ! If anyone wants to get rid od thier stock kenda's I will be glad to take them ! For dirt I wouold have to say the XCR's are my choice @ 4psi on all 4.