it isn't its two different things, man is this thread ever getting confusing.
so the tires don't relate to gvwr except that they have to be able to handle the total weight of the vehickle, but it isn't as simple as deviding the gvwr by 4 and getting tires that will handle that weight, to do your tire requirments you have to look at front and rear axel weight maximumbs and then get the tires that will support that, usaly you just go by the rear axel as it is capable of holding more weight, normaly. so lest say you have a rear axel max capacity of 7500lbs and a front of 6500lbs, forget about the fron and take the rear axel weight and devide it in two, that is the minimum tire capacity you should have. so each tire should be cabable of holding 3750lbs at their maximum inflation value (usaly 80 psi for a tire in that range) I like to go a little bit on the save side so I would look for a tire as close to 4000lbs capacity as I could find. but if you did take that 3750lb rated tire and multiply that by 4 it would be 15000lbs and the gvrw of the fictional vehicle I made up here is 14000lbs so you are covered doing it this way.
so if you know your front and rear axel maximum capacities (on that same door sticker) it is much easier to figure out what you need.