http://www.4x4mag.co.uk/novfeatures/novtyres.htmThis question always creates abit of a debate - but the link may help. The air inside a tyre is a way of tuning the tyres performance. Manufacturer recomended pressures are usually the best compromise to give grip, milage and safety for a wide range of loads, surfaces, and temperatures/conditions. Generally run the tyre at a high pressure and it will run cooler (heat helps grip), not be as comfortable but will give better mpg at the expense of uneven wear. Run the tyre at a lower pressure and the tyre runs warmer (helping with grip), may flex too much and wear unevenly with poorer mpg.
The mass of air in each tyre is dictated by the weight its asked to carry - the way to measure the mass in the tyre is by tyre pressure. Put biiger tyres on your truck - but don't change the weight youwill only need the same mass of air in each tyre. Bigger tyre = bigger space with same mass of gas = lower pressure. It gets more complicated than this but generally speaking experiment a little and see how the ride feels. You could do th chaulk test. Draw a line across your tyre and go for a short drive. If the line has worn evenly the pressure is about right. Chaulk left in the middle but no on the edge means pressure too low. Chaulk on the edge but not in the middle = pressure too high.
