How Fast For 12 Inch Tires

I will tow it 1500 one way, then same back with a light load if this helps

Every tire made on this planet has a speed rating.

4.80 x 12 Load Range 'B'.......45 mph

4.80 x 12 Load Range 'C'.......55 mph

4.80 x 12 'High Speed'........62 mph

I'd be more concerned with the tires than the bearings. I see a lot more trailers with snowmachines on them that have flats and blowout problems than I see pulled over for bearing problems. On my larger trailers for 50 - 100 miles trips to go snowmachining I often leave without a spare, but I never leave without one on my small two place trailer.

Bill

I'd be more concerned with the tires..

I have a 4'x8' utility trailer with the 12" wheels. I routinely tow it at 70 mph and have for years. I check the bearings and grease them every year.
Before this one I had a same size trailer with 8" wheels. Towed it the same way for many years until a guy ran into the back of me and crunched it. Replaced the bearings after several years when one of them got a little worn, but not failed.
Those little wheels scream at highway speeds but the hubs have never gotten close to being hot. I always feel them when I stop for any reason.

Weight has more to do with it than anything, other than the bearings not being packed well. FWIW I ran 4.80x8 tires on a MC trailer. Total weight was around 250lbs. I ran 70-75 all day. Tires were never hot, always cooler that the MC's tires. I packed my bearings my self so I knew they were good. Question is who made the trailer and how well the bearings are packed. If they are the cheapo china junk in there then I would replaced them with Timken's. Pack the crude out of them. And run 65-70 all day. If your loaded to the gills then maybe not.

Just keep bearings lubricated and don't overload or have improper air pressure in tires.