I have an older Bayliner bass boat. When I bought it a year and a half ago, it had 13 inch tires and rims but when I hit a large enough bump or dip in the road, the tires rubbed the fenders so I had an old flatbed trailer that had 12 inch tires on it that had the same weight rating as the 13 inch tires so I put them on the boat.

Since then I have replaced the leaf springs on the trailer and that gave me enough room to put the original 13 inch tires back on the boat trailer.

The 12 inch tires have served me well on this trailer but I have a couple of questions.

Does the tire size matter if the weight rating is within limits?

I never noticed it before but the original 13 inch tires are radials. I seem to recall that typically a guy doesn't want radials for a trailer. Is this true and if so, why?

The 12" tires will rotate faster and get warmer as you tow the boat.

I don't run radial "car" tires because they have soft sidewalls and I don't like the way it makes my boat feel behind the truck.  I get tires made for trailers with 8 ply sidewalls but I think they are still radials.

well acually the rim size does not matter, you can get tires that fit on 12" rims and they will be the same diameter as tires that will fit on 13" rims. just look at what the overall diameter is of the tire and go from there.

Well, looking at both sets of tires, the 12 inch are 8 ply biased ply tires, the 13 inch tires are radials and are about an inch and a half taller but they only have 1 ply on the sidewall so I'm assuming (for the time being anyway) that right now I'm better off with the 12 inch tires.

When I can get some money together, I'll buy some 13 inch biased ply tires but for now, I'll stick with the 12 inch tires unless somebody can tell me why the 13's would be better.

You can buy radials, just buy ST rather than P or LT.