Hello,

Our tires need replacing on our 2 horse BP.  We currently have Goodyear ST225/75R15.  They are rated to 2150 pounds, max PSI is 50.

I am looking to replace them with a similar tire. However, the Goodyear tire dealer dealer in town says that he only carries the 8 ply version of this tire.   He believes that the 6 ply (which he what he thinks I have currently have) has been discontinued.  The 8 ply is rate to about 2350 pounds with a max PSI of 60.

Would the 8 ply be OK?  Would there be any significant difference in the ride (for the horse of course). 

The 8 ply/load range D will be the better choice of the two... Are your rims rated at 65 psi. or less? Here's the Goodyear tire inflation chart. If your rims are only rated for 50 psi the 8 ply at 50 psi will still give you the smoother ride of the 6 ply and still have the same 2150# capacity. Remember, these "ST" special trailer tires are rated at 65 mph at 65 psi.

http://www.goodyear.com/rv/pdf/rv_inflation.pdf

Nope, the wheels must meet or exceed the psi of the tires.  So if the tires are say 2300lbs @60psi, then the wheels must be the same number or BETTER.

Went thru this 2 years ago on 16" tires and wheels.

As far as your original question goes, in my opinion tires and wheels are like trucks, you can never have too much.

In my case the numbers or information was stamped on the inside of the wheels.  I removed the tire/wheel from the trailer and it was on the inner side. (had to wash the crime off to see it)  Just a guess here but you might check with someone like southwest wheel or redneck trailer supply and they should be able to tell you what most of the 15" wheels are rated for.  I'm not real sure there is as many different 15's compaired to 16's.  I know in my case with the 16" I had 3 different wheel ratings on 1 trailer.

I found my tire and wheel specs.

Tire size is 225/75R/15C.

Wheel size is 15 x 6JJ

Will a D load tire work?

Run the new lrD tires on those rim at 50 psi, they'll do just fine.