Tires: Trialer Tires, nitrogen inflation, inflation pressure

Question
I just replaced my 205 75 R 15 C with 225 75R 15 D.  My horse trailer is rated for C load, but I wanted the extra weight load as a safety measure, in case I lose a tire, my other three D rated will not be stressed like 3 C rated.  Anyway, my specific questions is about air pressure and nitrogen. C load tires max air is 50 lbs, D load 65 max and E load (not sure).

I was told by many that low air pressure is the number one reason for a trailer tire to blow, then I was told by tire dude that running my D load tires with 5 or 10 lbs less pressure will give my horses a smoother ride?  sounds fishy?

I was told always keep trailer tires at max.  Where am I going wrong here and can you clear this up?

thanks

Answer
Rick,

First, here's what I've said about nitrogen inflation:

http://www.barrystiretech.com/nitrogeninflation.html

Short version, there's no harm, but the advantages have been greatly exaggerated.  If you can get it free, great,!  But I would not pay for it.

When you changed tire size, you also changed both the load carrying capacity at the same pressure, but also added the ability to use more inflation pressure - and therefore increased the load carrying capacity again.

Yes, low inflation pressure (more precisely, not enough inflation pressure for the load) is the biggest reason for tire failures.  You should check and adjust the pressure for both the tow vehicle and the trailer every time you use the trailer.

And, yes, lower inflation pressure gives a smoother ride.

So, why don't you inflate your tires to start at 65 psi, the weigh the trailer - fully loaded, please.  You want to do a worst case - and if you can, it's best to try to measure each tire individually.  But at the very least, you ought to weigh the trailer side to side.  

From that you ought to be able to figure out if it is safe to lower the inflation pressure for a more comfortable ride.

Oh, and I would use a 15% over capacity for the tires.  Put another way.  Pick the worst tire load an multiply it by 115% and use that to calculate the inflation pressures.