If the O/P has 20 and 40 foot options, I think we can all agree without a lot more information, he should go with the 40 foot option. There are times when I have put my rig with a 53 foot trailer down a 20 foot opening, but I really didn't like it and was sure glad I got the cooperation of a lot of people who took a few extra minutes to stay the heck out of my way. (1 mile from my house and an accident closed the road ahead, so I HAD TO take the detour down a side street with deep ditches on both sides. Knowing I would have the same issue at the other end of the street, I called my Bride and got her to come slow traffic down long enough for me to make another wide turn. Once She slowed, and I started out, a car passed her and ended up looking nose to nose with my rig. I just sat there till he figured out that I wasn't going into the ditch to make room for him after he passed my Wife on a double yellow line! He actually was nice about backing up in the wrong lane past my Wife so I could finish my turn!
( Sorry about the rabbit hole!)
David from jax
The slower you take a turn, the sharper of a turn you can make.
DfJ