Newbie tire fitment questions. Help!

[WBusa]

Here's the deal: we bought an old (but basically sound) small two-horse, twin axle ball-hitch horse trailer, model and year unknown. We've been towing it (in light service) for a year now. Just today I read the tire sidewalls, and my hair stood on end. My first problem is, they are garbage tires... no-name "made in China" with no DOT label, so they must be pretty old. They're P215/75-R15s. OK, so my second problem is these are passenger tires, which I now understand is a no-no.



With my confidence in these tires now thoroughly shattered, I measured the outside visible rim diameter of the wheels, which is 16 1/4"... so I'm assuming these are 15" wheels, since the visible rim diameter of my Ram (which I know is a 16" wheel) is 17 1/4".



Last but not least, it appears that none of the major tire manufacturers make an ST215/75-15 (well, there's a Badyear Wrangler HT in that size, but I don't want it). Now, I don't actually know that these are the right size tires for this trailer in the first place (no owner's manual, no sticker). In fact, considering they're passenger tires I figger there's a high probability that everything else about them is wrong, too.



So my two questions to y'all are these:

1. Measuring the wheels as I did (i. e. , to the visible edges, with a tire mounted), am I pretty safe in assuming these are in fact 15" wheels?

2. If I can't find LT215/75-15s, how much latitude do I have in playing around with the first two numbers? For example, Cooper (I love "Made in USA"!) makes a LT235/75R15 in its SRM II Radial LT. If I made sure it doesn't rub the fender, the wheel well, or its companion on the other axle, could I substitute this size for the existing 215/75s? Or are their additional considerations involved besides just clearance? (I have a feeling this is a really dumb question... like I said, I'm a newbie when it comes to trailers).



I really wanna get this right, because horses all over the highway is really bad news. Thanks for your help!

 

[Cryppie]

I'd say you're safe in assuming 15" rims, anything other than that would be really out of the ordinary. 235's are only about 3/4" wider, and just over 1/2" taller than your current tires, not much difference. I'd definitely go for the highest load rating you can, carrying live animals I'd want the greatest safety margin possible. I'm going to be running LT tires on my new car hauler, as 16" trailer tires are rather hard to come by. Just ensure there is enough clearance to compensate for tires growing from going down the road and suspension travel, and I'd feel safe pulling your trailer. Good luck!