Length, width dependant sometimes on what angle to try to leverage the package by; then figuring out if with those maximazations you are within reach.
Sometimes cuts are saved in longer logs, using their length as leverage and counterbalance to help load their own selves. Sometimes make it walk up a 3 " step, just to get more weight high lean over the pivot of the trailer edge and throw down to lift other end, if it won't just load self etc.
In wider than long weights, sometimes in textured bark i have luck making a ramp out of a half round of trunk that serves up to rib of trailer. Then instead of lifting so much, push the texture of the piece being loaded into the texture of the 'ramp'; to make them mesh like gear teeth and roll up, pushing into the rib of metal on trailer as next gear tooth and roll up slightly; trying to leverage more than lift, allows a ratcheting or kinda better load holding off of you as it advances too. Saving more energy to task of advance than hold; and enabling gathering to burst/impact forward to move load etc. Lean to save back, not lift!
With smooth ramps, some stumps seem to slide up on flat shaved side rather than roll. Kida hold themselves while ya take break too.
If it is long leverage it, round-roll it, heavy-counterbalance it across a pivot.
Here is a pic. of a parbuckle i made for side loading perpendicular to the axle. The ancient parbuckle (listed as a knot some places)will give the power source (truck) ~2x pull(of truck); and roll a round load without a pulley as it performs too. Depending on weight of load and edge of trailer etc., might not even need ramps, but of course the MA of ramps amplify the effect of the 2X1 truck pull of a rolling load. With sides, you would have to pull to front with truck or try to redirect to back with pull line possibly, not rubbing load; so trailer should be even more secureley chocked pulling on the roll angle of the axle. We've side loaded 20' poles at least 4 high full across many times easily. One of them Blue Sherrill Log Ox's or other arch sure is nice for laying a pole in the belly of this rig!
