62Blazer
Senior Member
Yes. The "max PSI" is just that, the maximum safe pressure you can put in the tires and should never exceed. Inflating the tires to a higher PSI means you are starting to risk tire failure from them blowing out (not saying putting 55 PSI in a 50 PSI max tire is going to cause it to explode because of the safety factor built in....but I'm sure if keep increasing the pressure at some point they will fail). It does not say you need to run that pressure...just not exceed that pressure. The weight rating of the tires is basically a direct correlation to the inflation pressure. The max weight rating of the tire is at the max PSI, so if the tire is rated for 3,000 lbs. max and 50 PSI max that means the tire can support 3,000 lbs. at 50 PSI. As you decrease the inflation pressure (PSI) of the tire the weight rating goes down proportionally. The rule of thumb is if you decrease PSI by 10% you decrease the load rating by 10%. In this case that would be dropping the inflation down to 45 PSI and would decrease the weight rating by 10% also, which would make it around 2,700 lbs. Drop the PSI in half, so 25 PSI, and the weight rating is dropped in half to about 1,500 lbs. **Just to clarify, this is a general rule of thumb to get you in the ballpark. Typically easy to find load inflation tables on manufacturers website that give exact numbers**.So if it says the max PSI is 50, does that mean I should be fine with say 45 front and 40 rear? I'll rarely haul anything with much weight in the bed if rarely.
With that said if you have tires rated around 3,000 lbs. each times 4, so around 12,000 lbs., and the truck weighs maybe around 7,500 lbs. That means you only need around 63% of the tires weight rating to support the truck. 63% of 50 PSI is 31 PSI, which means that running in the 40 PSI range is perfectly safe. Keep in mind this is assuming equal weight front to rear. On a pickup when unloaded the front is usually heavier and thus why most people run higher front pressures when unloaded. I generally like to run a little more PSI than what the equation states, but it at least says if you are in the ballpark or not.
As the last statement, the max PSI and load ratings are also for max speed rating of the tire. The higher the speed the more stress/force on the tire. Lower pressure causes the tire to flex as it rotates and the bottom of the tire flexes under the weight of the vehicle. The more it flexes, the more stress and heat build-up. Basically means that the slower you are travelling the less critical and less chance of failure if you are not running the appropriate inflation pressure. If you have a tire really low at 10 PSI you can drive for a really long time at 15 mph with no damage, but go drive down the freeway at 80 mph and it will have permanent damage after a short distance and probably fail (blow out) if you keep going).