Tires: passenger vs light truck, LT vs P Tires

Question
I have a Nissan Titan 2005 which has 245/75/17 tires.  I ordered 4 Michelin LT tires for it but was told not to put them on by Sam's club because the original tires are passenger rated.  P rated tires are very limited in this size and are not highly rated.  Different tire shops are telling me very varied things, some agreeing, no LT tires and that if I do gas mileage will suffer greatly.  Others saying LT tires are better, but you just follow the lower pressure inflation rates recommended by the car manufacturer.
Who is right.
Thanks
Joe

Answer
Joe,

this isn't a case of right or wrong.  This is a case what's the best.

Yur truck came with P metric tires - P245/75r17 - and the rest of the truck was designed around that tire.  The springs, shocks and sway bar were designed to accommodate the spring rate and damping coefficients that the pressure spec of 35 psi would have.

LT metric tires are designed like their bigger brothers - the over the road truck tire - and require a higher pressure to carry the same load.  this is because the rubber compounds are not designed to be flexible - as in the case of P metric tires - but were design to stand up to a lot of concentrated load.  Assuming you are using the same size as the original except that is an LT metric, you would need to use 50 psi.

This pressure would result in a significantly different spring rate and shock damping setting if Nissan had been setting the truck up.

I am not a fan of using LT metric tires in place of P metrics. But some folks report good results, so it's difficult for me to argue with success.