After trying alot of different oils & oil weights (outta boredom really!) I found that if u do not match your oil weight in a Harley engine to outside ambient (air) temp. the engine will over heat.

If the temp. is gonna be above 30C I would go for a 20w 60 or whatever.  If it's getting on for 50C a 70 weight.    The 50 weight thins out alot & raises the temp. on a 38C + day (black smoke too).    The same goes for using an 60 weight in winter it will raise your cylinder heads temp. a shit load. (This is different too cars).

Just some advice. 40/50 winter 60/70 summer.