Personal opinion, put in in service and maint section and sticky, anyone else agree?
(FYI I made a Oil Change DIY for my last bike some 5 years or so ago.. It was made a sticky and the thread dominates the entire forum on "Thanks", you become the man for this and end up having more thanks than anyone else)
I'm not sure there's any science behind it. When I was a n00b the crew I rode with all used 20W50 in their R1s and gixxers for years. They claimed that as far and hard as we pushed the engines, a little thicker oil would help protect better than 10W40 since it would resist high temp break-down better.
I'm seldom a follower but in this instance I just followed what my peers did. I know over 25 riders who have used 20W50 for years as well as 3 mechanics and two professional drag racers who all use or recommend 20W50 over 10W40 even when the book calls for 10W40.
Not sure there's any real gains but it obviously doesn't hurt either
lol oh well i thought it was 10w40 too till i looked at the dealer and they didn't have any 10w40 so i just went with the 20w50.
the 20w50 will be fine for now until i switch to synth, a little thicker and maybe a little less horsepower probably not even a single hp though. for you in washington i would stick to 10w40 as the climate is not as hot as down here in texas.
I have though about going to 5w40 or possibly even 0w40 for winter.. I dont notice it on the 300 but on the 250R it just dosnt feel right until the oil them is above 40 or so.. (I have an afteramarket gauge cluster on my 250R so I got oil temp and water temp)
I ride in all weather, unless there is snow on the ground