Why Only 6 Ply Tires?

[kneedeep]

I don't think they are quite that bad. Again, it's about buying the right kind of trailer (and ramp/gate, etc.) for the job.

I humbly disagree.
Anything with 2 axles is probably 7K rated minimum regardless of how the trailer is built. That is the rating for the 2 3500# axles and not the tires or trailer. Smaller axles are for singles with 13 and 14 inch tires. Those cheap trailers are not well built for hauling maximun axle loads. Thats why they are so cheap. Most SCUT will haul on them but they are real easy to overload. Most have no engineering to back them up.
Buyer beware! Do your homework before buying a trailer, a little research could save a lot of trouble down the road.

PS
Everything I have looked at carries at least 8 ply ST tires on 7K# axles. I have spec 18' and 20' trailers that weigh up to 3000#. If the estimated weight is 1200# why is it so much lighter? Smaller steel maybe??

There are a LOT of cheap trailers out there and you do get what you pay for.

 

[JIGBUILDER]

Trailer manufacturers choose tires per 571 FMVSS's which say in part ......the sum of the maximum load ratings of the tires fitted to an axle shall be not less than the gross axle weight rating (GAWR) of the axle system as specified on the vehicle's certification label required by 49 CFR part 567.

The manufacturer isn't required to use a specific size or load range tire. Just capacity. Most 7k gvwr trailers with 3500 lb axles come with C load range tires in a 225/75-15" @ 2150 lbs of capacity at 50 psi or even 205/75-15 @ 1820 lbs of capacity. Plenty of tire for a 3500 lb axle.

IMO the 8 ply rated D tire has 2540 lbs of capacity at 65 psi requires a wheel upgrade. The trailer manufacturers know some folks will overload their trailers if they use over rated tires and wheels.

If you need 8 ply tires you need the heavier rated wheels/suspension/axles and trailer frame for the job.

 

[slowzuki]

Ditto.