Tires: xl tires and lt tire ride quality, inflation pressure, basic principle

Question
same size tire but an xl, it can carry more weight with additional air added to it above max inflation of same tire in standard load.  what is different about an xl tire physical content to give it the xl ability.

Answer
Dennis,

The basic principle is that the load a tire can carrying depends on many things - and inflation pressure is one of them.  But there is an upper limit for the inflation pressure.

But if you build a slightly stronger tire, then you can use more inflation pressure - and therefore carry more load.  By "stronger" I mean a stronger ply material (larger ply cord and/or more of them), and a stronger belt material (larger belt wire and/or more of them).

Another basic principle:  Ride quality is more a function of inflation pressure than it is of construction.  Only experts can sense the difference between SL and XL tires.

But I sense that you're really asking about the difference between XL P metric tires and LT metric.  There are a couple of other things you need to know.  P metric tires are derated when used on Pickup trucks, where LT metrics are not.  As a result, I can not recommend that folks replace LT metric tires with P metric tires (even XL's!)