I've been having a little disagreement with someone that I hope you guys can help decide. He says that if you have a tire with a max load of 35 psi and you inflate it to 30 psi that it will be fine, which is all normal but the catch is he also says that if you took a tire of the same size but with a max load of 51 psi and inflated it to 30 psi, that it will be under inflated. His argument is that the tire should always be inflated to 80% of the max load or it is under inflated. The thing is that many people have tires with a max load of 51 psi and they are readily filled to around 30-35 psi (such as mine) and exhibit no wear symptoms of under-inflation. I may just not be able to understand it but I don't see how you can have two things of the same exact volume, inflate them to the same pressure, yet have one be normal and one be under-inflated. As far as I was concerned the max load rating was just how much the tire could hold before it started to become unsafe. Sorry for the length.