Another Tire Question

Just curious, what are the downside problems related to an "over tired" trailer?

Tire experts and experienced trailer owners have found tires on a trailer work better long term when their ran at max sidewall pressures mostly to protect the tires carcass and tread belts from ply shearing as the tire side slips/ while backing or just pulling the trailer around a corner. At some point the tire has too much capacity to use max pressures.

Tireman9
one of our tire engineers also recommends max sidewall pressures says; from rvtiresafety.com his online tire blog;

"The manufacturers do not take into consideration the side to side unbalance, as to do so would require them to provide larger (more expensive) tires. The other thing RV industry does not take into consideration is the forces to the tire structure due to running close axle spacing. Engineering analysis shows that when turning corners the forces trying to tear the tire apart can be over 20% higher in multi-axle applications than with tires at the corners of the vehicle.
The only options for the trailer owner are to up-size the tires (if there is room) or up-rate and increase inflation (if a higher Load Range tire and stronger wheels are available). Lacking the above being sure to run the tire at the inflation shown on the sidewall (i.e. max) will slightly decrease but not eliminate the overload forces.
and
When not driving in a straight line there are special side loads on multi-axle trailers because the tires are fighting each other because they are not "pointed" to the center of the radius of the turn. These loads cause interior structural tearing. Sometimes 24% higher loads than those seen in tires on non-trailer application. Initially tearing is at the microscopic level but with time and repeated cycles these forces grow which can lead to small cracks at the belt edges as seen here at the arrows.
and
You can lower these forces by either decreasing the load 24% on the tire (probably not something you want to do or may not be able to do) or you can increase the inflation to stiffen the structure and decrease the slip-angle. In this case you could increase the tire inflation from the minimum inflation needed for the static load to the inflation associated with the max tire load as molded on the tire sidewall. "
and rvtiresafety.com

Spend some time on his website. He has some very good actual tire tech especially about tires used in a trailer position. Tireman9 isn't just another rv guy with a blog.