houtrz wrote:
...what is actually safe,...
"Safe" towing depends upon a lot of things. The skill of the driver, the soundness of the equipment, the conditions of the road, the time of day, the weather.
It's "safe" to tow a trailer at 60 mph on a straight road in the middle of an Arizona Summer. Is it "safe" to run 60 mph on snow covered roads in the mountains of Virginia, even if the speed limit is 70?
There is no "right" or "wrong" answer to the word, "safe". What is safe for one is danger for someone else.
A 10 year old kid can climb a tree and he's safe to do so. A 70 year old with hip and knee replacements climbing the same tree is just .... dangerous! Same tree? What's the difference? The tree hasn't changed.
Perhaps the better question to ask, what is, "What is an an appropriate speed for YOUR outfit!" Here again, that depends upon your towing ability and skill, the dependability of rig, if you are loaded and hitch appropriately, if the weather and road conditions are relative good. If all of this is "true" then, perhaps the best answer is, the rating of your trailer tires. Any speed greater than that, you are taking a risk.
But you know, some of us old men still like to climb trees! Not the smartest thing to do, neither is pushing the max speed on your trailer tires. But it happens all the time.