This is what I do for a living and there are some interesting points about some of the great advice not to mix them from others who already posted here.
I think the OP was probably referring to P series tires and LT's. In my opinion it is best to have all 4 tires exactly the same and to not even mix new and well worn tires. Especially on 4X4's. A tire with 40,000+ miles on it will essentially be one size smaller in diameter than an identical new tire.
"I think the OP was probably referring to P series tires and LT's."
I think you are right because the "Aspect Ratio" of all tires except a few All Terrain size designations such as 31x10.50 or 33x12.50 are now measured in Metric. So "P Radials and Non-P Radials" would lead me to think this is what the OP meant and it is a difference between Passenger rating and Light Truck rating. And a LT is always shorter than the same designated size in a Passenger rated Tire.
Here's something interesting about this statement I would like to share.
"A tire with 40,000+ miles on it will essentially be one size smaller in diameter than an identical new tire."
Actually believe it or not, a Tire tends to stretch and swell a bit during it's lifetime. So it is not uncommon to stand a bald tire next to a Brand New one of the same brand and model and have the Bald one be as tall or even sometimes a little taller than the new one! Sounds crazy but it's true.
But what you say is important about not mixing worn with new because they do indeed handle road conditions a world apart. Ever notice how a new set feels just a little "squirrelly" compared to the old ones for a few days until you get used to how they feel? This is because you just added almost an inch of "Flexible" Tread Rubber that your old "tight" Racing Slicks did not have.
I see a lot of guys that buy tires 2 at a time on a 4x4. Mostly of differing manufacture. I prefer not to. Kind of like buying one shoe. mtmuley
Absolutely...and here is something we should all know and raise hell about. Unfortunately there is no Industry Standard for maintaining the "actual Size". They use what is called "Designated size" as a loophole in the actual size of the tire produced even though they are "Designated" as the size advertised and marked on the Tire.
This means that even though two different Brand Tires are designated as let's say 235-75-R-15 it doesn't mean they are truly those exact measurements like we are led to believe or think they are. There can be a huge difference in the actual size of one Manufacturer from another. I have measured sometimes up to an inch difference of the so called "same" Tire size between one maker from another.
This is why what you say about mixing Brands on a 4X4 is so important, especially on newer model 4X4 and All Wheel Drives that have front hubs that cannot be "unlocked". It will eat more expensive stuff up.
Thank you for letting me share these important points!
