How to calculate turn radius of fifth wheel for new driveway

A: parking lot big enough to turn a full circle.

B: a friend (or spouse) with a can of spray paint and a sense of humor.

Plan to go around the full circle three times.

circle 1 - paint a dab about every ten feet where the inside front wheels of the truck track.

circle 2 - paint a dab where the inside front wheel of the trailer tracks.

circle 3 - paint a dab where the outside tail of the trailer tracks.

Connect the dots if you wish.

Remember that results in the real world will probably be wider than under controlled conditions.