Also, -R+r doesn’t really work as it cuts away all the bulge on the eastern and western hemisphere. See this Winkel Tripel globe with -R-180/-90/180/90+r:
gmt coast -R-180/-90/180/90+r -JR12c -Bg -Dc -A10000 -Gburlywood4 -Swheat1 --GMT_THEME=cookbook -view GMT_winkel-R+r
For clarification: -R+r works exactly as expected, it just doesn’t really help in this case.