It consists of having the first person who gets in the back seat sitting with their ass either touching the backrest(as you would normally ride) or sitting with their ass as close to the edge of the seat(and as far from the backrest) as possible. From their, everyone alternates ass to front ass to back until you can't fit anymore people.
This is proven effective.
"It's chill we'll just sit with alternating asses and be good to go."-Guy 2