Truck Tire inflation question
 

I know this might sound retarded....but i don't understand a few things about my tire pressure.

I have 35" Nitto Trail Grapplers. The sidewall states the maximum pressure is 65PSI (cold Pressure). So with that said, what is the best tire pressure for daily driving? Is it like 60 or 55 PSI or what. Probably stupid question, but i just have no clue.

The psi on the sidewall is the max pressure the tire can handle under the specified load. The psi recommended by the truck manufacturer is the psi that the manufacturer determined to be the best for giving the truck the handling and ride (softness or hardness) that they were trying to achieve. However, the manufacturer's psi may not provide you with better gas mileage.

I personally like my tires at the max pressure the tire can handle. For one I get slightly better gas mileage. Secondly, I like the way the truck drives and handles with the tires at max pressure. When my tires are at the manufacturer's suggested pressure I feel like my truck is sluggish and doesn't turn as sharply. When the tires are at max psi the ride is slightly bumpier though, but it doesn't bother me. It's all personal preference.

What is the actual increase in MPG from over inflation? Does that save you more than the cost of replacing tires more frequently? I'd wager overinflated the truck doesn't stop as well either. Just my two cents...

To the OP, it depends on weight of the truck really. I'd start at 50 PSI and wee how they appear to be making contact, see how it drives, watch tread wear and contact pattern. More weight means you need more pressure. Running around either over or under inflated will make the truck handle poorly and wear out your tires more quickly.

i usually go with max psi also. more often than not your pressure is the hot pressure when you go to fill them up so you need a few more psi anyways to compensate for what the cold psi should be.

The ideal pressure is related to the surface area of the tire and the weight it is carrying. Yours are much larger than stock so you could run lower pressure than the stock recommended pressure for your truck. If your recommended pressure was 45 you might be fine at 35. Running the max pressure will decrease your fuel use but putting on those tires killed any concerns you had about fuel. It also increases the wear in the center of the tire so you will have to replace them sooner.
If your pressure is too low the truck will wander and feel like it floats. It also increases the sidewall flex which generates more heat in the tire. That can lead to tire failure. So what would I do? I think I'd run them a bit too high for the reasons Richard stated and then lower them quite a bit if I was going off road. (By that I mean at the stock tire pressure or slightly above.)
You can get a tire pyrometer and measure the temperature across the tire to determine the optimum pressure for wear and then raise it until you get the best 'feel' for your driving.