For those of you running 30x9.5x15 tires.What PSI do you fill them to ?
My tires say 51 psi,the guy that mounted them said 40 psi is plenty.
What do you guys think ?

 

Whats your use?
Higher pressure will give stiffer ride and better MPG

Lower pressure a softer ride and less MPG with more traction

Traction is friction, and anytime you increase the friction you decrease the MPG, laws of physics

So really up to you for "what is best"

Tire makers are concerned with the miles their tires can go before wearing out, so would be partial to higher pressure, because there is less tread on the road so less wear on the tire.

You can start with 50psi and if ride is too harsh, lower it down