Tires: 6 ply, tire placard, chevy 4x4

Question
i do a lot of driveing on gravel roads with a half ton chevy 4x4 pickup and i wanted to know how a 6 ply toyo at's would do or should i get an 8 ply

Answer
Mike,

Let's start at the beginning:  

On every vehicle sold in the US - and I understand this is a worldwide practice as well - there is a sticker – commonly called the vehicle 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.

One word of caution:  Some trucks use tires with the letters "LT" in front of the tire size - and some trucks use tires with the letter "P" in front of the tire size - and some trucks use tires with the letter "C" after the tire size.  You should not use "P"'s in place of "LT"'s and vice versa.

For this situation, you should be sure the pressure on the sidewall equals or exceeds that pressure on the placard.  If you do this the issue about the letter "C" in the sidewall will take care of itself (which is not true with "LT"'s vs "P"'s.)

If you are using a tire size that is different than what is listed on the placard, then the pressure has to be recalculated.  The calculation is not difficult, but it requires tire load tables which are not allowed to be published in the Internet because of copyright laws.  However, I have a copy and would be glad to do the calculation, but the starting point is the vehicle placard: Tire size and inflation pressure.  I will also need to know the new tire size.

So your first step is to determine what your situation is.  Did your vehicle come with P type tires?  I'm guessing yes.  If that is the case, then P type tires do not come in Load Ranges (what you called "ply") and you need to select a tire that is designed for your driving condition.

If your vehicle indicates that the tires are LT type tires, then the pressure listed on the vehicle tire placard will determine if you need a Load Range C or a Load Range D.  Again, you need to select a tire that matches your driving conditions - and the "plies" is not what determines this.