Why is it better to have the tandems slid forward when alleydocking?

I think you answered your own question but don't realize it. If space is limited having the tandems slid forward will make your trailer react quicker to your inputs from the steering wheel. But the con to that is more tail swing. If there was a truck on both sides of your dock you'd have to worry still about the tail of your trailer hitting truck next to you. Really it's probably a matter of personal preference in every situation and doing what works for you after a million miles.

 

Because sliding your tandems forward essentially makes your trailer shorter. Shorter is always better with limited space.
But again it depends if there's something on the other side of your dock that you have to worry about backing your trailer into.

 

In your drawing where there is nothing to worry about on the east side of your dock, and assuming space is limited in front of your dock. And as far as the turning part of your maneuver into the dock. The trailer being 53 ft doesn't matter. All that matters is where the trailer tandems are. Pretend your trailer does accordion when you slide your axles forward or back. The trailer tandems are the pivot point. Tandems slid up equals tighter turning.
But again in this scenario you aren't worrying about your tail, because it doesn't matter, there's nothing for it to hit. But in reality that rarely happens.

 

Well, think what your trailer is going to do if you were in that dock with your tandems all the way forward and you pulled out till they were just past the tractor to your left, and you hang a sharp left, your tail swing will most likely hit whatever is on the right side. Now do all that in reverse, like your going to bump the dock, and take out the term "tail swing" and replace it with overhang. As far as what other drivers say about whats best or whats right as far as your backing, who cares as long as it works for you.

 

I often did that when I had an air slider on my Trailer. Maybe he’s jealous. Maybe he should be asking you why, instead of telling you how. Whatever works best.