Single or tandem axle

The most critical part of the equation is the distance from the pivot point to the axle. The greater the distance the easier it is to back up.

That's why a boat trailer is easier to back up than a short utility trailer.

Are single or tandem axels easier to back up and why? I have owned both and think a dual tandem axel is easier to navigate into tight spot but don't understand why. A single axel seams to jack knife more.

Longer trailers are typically easier to back up than shorter ones. Most longer trailers are tandem axles. Maybe that helps in sorting out your question.