Just bought a nice little Titan trailer two horse (ok I'll squeeze in three) slant load bumper pull with a tiny dressing room.  GVWR is 10,000 lbs, but my bet is the trailer is 3500 lbs and the horses another 3500 lbs.

Need tires, and my dealer is suggesting an ST22575R 15.  what on there now is a 70015LT 

Can someone tell me the pros and cons of 1) Gladiators and 2) that size and LR vs. ST?

Does the R (I assume that's Radial) make a big difference?

As always, many thanks.

Most of the newer sizes will be quoted in metric tire size number like this

ST225/75R15  or LT235/85R16

The letters are the vehicle type.  ST = Special trailer,  LT= Light Truck  P = Passenger

The first numbers are the Section width in millimeters

The second number is the Sidewall Aspect Ratio. This number represents the % of the section width

The next Letter tells the internal construction type.  R= Radial Body Plies  D= Diagonal pattern  B= Belted

The last number tells the Wheel size.

Any letters after the wheel size generally refer to the Load rating.  "C" rated tires usually run at 50 psi, "D" rated truck tires usually run at 65 psi and "E" rated tires run at 80 psi. With each jump in psi, You get a higher load capacity.

In general ST tires have a stiffer sidewall and a hiway tread.  Since they are not a steering or traction tire, They usually have a smaller tread designed to run cool with out heat build up.   You will often see LT tires substituted for ST on trailers.  The trucks also have the load capacity to carry the weight of a trailer.  But often truck tires are designed for traction and have deeper and more aggressive treads.

You will still find some tire size that use the old english numbers vs the metric.  Number like 35x12.5x20 

This means the tire is 35" tall by 12.50" wide and fits on a 20" rim. This number method is mostly still used on floatation tires for mud or sand..  They run at lower air pressure for better performance in the softer traction materials. And are probably not suited to use on a trailer.

For your purposes, I would look for a tire that is the same hieght and width, so that you don't have any rubbing. If you are going to squeeze an extra horse in your trailer, I would definitely be looking for some extra load capacity.  (Maybe a "D" rated tire vs a "C" rated)  This would give you an extra few hundred pounds of load capacity per tire. Definitely stay with a ST or and LT with a highway tread.  You don't need a All Terrian or Mud Tread.