The idea behind an aluminum trailer verses steel construction is the tare weight. Aluminum, being lighter than steel, more of the gross weight is dedicated to the payload. An unladen aluminum trailer weighs less than a steel trailer. An aluminum trailer is robust enough to handle legal loads. Depending on the number of axles, I have seen 4 and 5 axle aluminum trailers with gross weights of 125,000 lbs. A tandem spread axle is 80,000 lbs.