Typically there is a letter prefix attached to the size on your tires somewhere. It’ll either say P275/65R18 or LT275/65R18. It also should have a load index and/or a load range printed on the sidewall somewhere that can help. The load index will probably be a 3 digit number followed by a letter. The load range will likely be a C or an E if it’s there. The max inflation pressure printed on the sidewall will clue you in too. A standard load tire will likely have a max of 50-51psi with most owners running 32-36. Most LT tires have a max of closer to 80psi with owners typically running 40-50 for optimum comfort and wear.

P stands for passenger and denotes a standard load tire. LT stands for light truck and denotes a heavier ply tire with a load rating above standard. This is a bit confusing as you might think “light truck...sounds like what I have so I need those”. But the reality is that 95% of new half ton trucks come with P tires from the factory and the majority of owners never need anything else. If you haul a heavy payload regularly or tow something sizeable frequently then LT tires might be for you. The heavier ply and increased weight rating might make your truck feel more firm and planted when hauling or towing and you theoretically have less chance of a tire failure event with a heavy load. The trade off is that the ride is typically a little firmer all the time. That’s not to say it’s harsh. Some people like the firm ride an LT tire provides. Personally, I haul the trash, bikes, furniture, and might pull a small trailer with a load of mulch or stone once a year. I’d never put LT tires on my truck for my uses. If you pull a commercial landscaping trailer, large boat, camper, or car hauler, then LT tires would probably be beneficial.

M+S means the tire meets a certification spec for mud and snow. Hope this helps.