QuestionI have a 2002 GMC envoy, I bought some new tires 245-70-R17 LTX A/S from a friend of mine real cheap, the tire says to put 80psi, but my wife tells me it rides rough, I know they are heavy duty tires because they come off of a 2010 3/4 ton dodge truck, but I was wanting to know what is the least air pressure I can run on them, would 50 or 60psi be ok. thank you
AnswerRene,
On every vehicle sold in the US - and I understand this is a worldwide practice as well - there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size. The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.
BTW, it doesn't matter who makes the tire or what pressure is listed on the tire's sidewall, if the tire size is the same as the placard, then the pressure listed on placard is also appropriate.
According to Tire Guides a 2002 GMC Envoy originally came with P245/65R17's inflated to ....... well it seems there were a variety of configurations and a variety of inflation pressures, so it is now very important that you find the placard, because I am going to assume it says 35 psi, and go forward with the calculation with that assumption. If that is not right (or anything else I wrote) then what follows is also incorrect.
So assuming P245/65R17's at 35 psi, an LT245/70R17 needs to use 38 psi.
BTW, I am not a fan of replacing "P" type tire with "LT" type tires as you have done. They are designed for different purposes - and one of the ways they are different is the way inflation pressure is handled.
