I went down to HF to check out the trailer and the wheels. Stock wheels are 8" rims(16" diameter tires). One can replace them with 12" rims(20" diameter tires). They appear to be interchangable. However, the 12" rim is also marked "Do Not Exceed 55 mph".
Rough calculations show about 1260 rpms at 60 mph for the 8" rim/wheel combo, and 1009 rpms for the 12" rim/wheel combo.
Here in sunny CA, 55 mph is the max for any vehicle towing a trailer. But, I know some states are as high as 75 mph. So, it is best to be prepared for the extra speed.
I know the load capacity is listed as 600 lbs for autos and 200 lbs for motorcycles. So, I wonder if that 55 mph is for fully loaded at 600 lbs.