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P size tires (which came with our trucks) are load rated at 35psi. When P tires are used on a truck or SUV, they are derated by a factor of 0.91.
LT tires are load rated at different pressures depending on what load range they are:
C - 50psi
D - 65psi
E - 80psi
A tire's load carrying capacity is based on it's rating and it's pressure.
load/max load = pressure / max pressure is the conservative way to rate them (there are others which involve a power factor however this is a more conservative formula)
if you have a P tire and an LT tire the same size, the LT tire will require higher pressure to carry the same load.
for instance, you have a brand F 265/75/16 P tire (SL rated) is good for ~2604lb*0.91 (2368lb) at 35psi on a truck, the same size tire in load range 'C' is good for ~2484lb at 50psi but only 1738lb at 35psi.
now, say you have a truck that weighs 4450lb with a 57/43 f/r weight ratio, thats 1268lb on each front tire and 957lb on each rear tire. now add max payload (and assume it all goes to the rear wheels) of 1418lb and you've got 1666lb on each wheel. pretty close to that 1738...
at least thats what I got out of my research into tires...I'm sure someone will chime in. if you can get loading charts from the manufacturer, even better (but there is some research that suggests that the power factor used by most manufacturer's leads to too high of a load value at lower pressures...where the numbers were arrived at through testing is another story though)
LT tires are load rated at different pressures depending on what load range they are:
C - 50psi
D - 65psi
E - 80psi
A tire's load carrying capacity is based on it's rating and it's pressure.
load/max load = pressure / max pressure is the conservative way to rate them (there are others which involve a power factor however this is a more conservative formula)
if you have a P tire and an LT tire the same size, the LT tire will require higher pressure to carry the same load.
for instance, you have a brand F 265/75/16 P tire (SL rated) is good for ~2604lb*0.91 (2368lb) at 35psi on a truck, the same size tire in load range 'C' is good for ~2484lb at 50psi but only 1738lb at 35psi.
now, say you have a truck that weighs 4450lb with a 57/43 f/r weight ratio, thats 1268lb on each front tire and 957lb on each rear tire. now add max payload (and assume it all goes to the rear wheels) of 1418lb and you've got 1666lb on each wheel. pretty close to that 1738...
at least thats what I got out of my research into tires...I'm sure someone will chime in. if you can get loading charts from the manufacturer, even better (but there is some research that suggests that the power factor used by most manufacturer's leads to too high of a load value at lower pressures...where the numbers were arrived at through testing is another story though)
