The tires are specified to run on recommended inflation pressures by the manufacturers according to certain norms. What are they?
Answers
When putting air in tires, should you go by the door jamb PSI or the tire sidewall PSI?
Automobiles and tires have been on the road for well over a hundred years but many drivers are still confused about tire inflation. The first thing to understand is the air pressure listed on the door jam is the recommended pressure on your vehicle at RATED vehicle load, it is a good starting point. The pressure that is listed on tire is the maximum inflation at a specific load. It is listed in US and metric measures per tire in cars, trucks are list as single or duals. Manufacturers also listed tables of recommended inflation pressure at different loads, but only the tire dealer has that information as it is listed in manufacturer's engineering/product catalogs.
The pressure you should run is based on your normal usage. A majority of cars are loaded down with only one passenger, the driver, with hardly any significant load other than a spare. Likewise trucks nowadays are used as utility vehicles rarely carry a fully rated load like commercial vehicles. Over inflating rear tires will cause a rough ride and handling problems (over steer), especially at braking. A lightly loaded pickup will cause a diminished tread signature on the pavement. On icy roads and under severe braking situations rear tires may lockup causing dangerous handling (fish tailing) problems. That is why when anti-lock brake systems were introduced back in the 80's, trucks have rear anti-lock only, and did so for a number of years before 4 wheel anti-lock were standardized on all vehicles.
The pressure you should use is to follow the manufacturer's recommendation listed on the door jam on front tires. The rear tires use less pressure if your cars is a one or two person commuter without a significant weight on the rear axle. Front tires will wear much faster than rear tires as loading on the front of most vehicles are relatively uniform but additional loading during cornering, driving, especially FWD vehicles and braking put more demand on the front tires. Take a look at the size of the brake hardware on the front vs the rear. Disc pads on the front of cars and trucks are sometimes double the size compared to the rear, likewise rotors and calipers are larger too.
To get the exact pressure on the rear for your type of driving the best scientific method is to use an infrared or non-contact optical thermometer. Drive your vehicle on a warm day and scan the rear tire temperature across the thread. If the highest temperatures are at the center of the tire, then the tires is overinflated for your driving and load. If the two edges are warmer than the center, then the tires are under inflated. Adjust them until the temperatures registered across the thread are even or close to even.
The above mention method can also used to detect wheel alignment problems. For example, if the left front tire has much higher temperature on the tire’s outside edge compared to the middle or inner edge, it can mean a positive camber problem. If both front tires outside edges are warmer than the inside, it may mean positive camber, but most likely toe-in problem. If both front tire inner edge gets warmer than the middle or outer edge, it may be a negative-camber or toe-out problem. With the vehicle parked, move your hand across the tread of the tire, do you feel “feather edges” on the treads. If you do, the toe adjustment is likely off. Take the vehicle to an alignment shop and have the suspension inspected and repair if needed.