So I've made the change between
 

This

http://www.gz250bike.com/forum/attac...1&d=1433013564

And this 20w50

http://www.gz250bike.com/forum/attac...1&d=1436925058

And burned a tank of gas....

Fuel economy is up slightly. (statistically a wash)
Gears shift smoother.
Engine case is notably quieter.... Changing oil every month so not a fresh oil
used oil kinda change..... This is a viscosity change.

This is all in 80F (26 2/3) morning, 100F (37 3/4) afternoon riding.

My conclusion... In Southern US states in mid summer a thicker oil is a good
thing. However... I would never run 20/50 in the cooler/cold months.

I will continue to run 20w50 for at least 2 more months....

I will let you know if my oil pump fails or my motor blows up ;) :P

Disclaimer:
Owners manual says 20w50 IS an option.
I decided to pursue this option even though the fill cap for the engine case clearly states 10/40.
If you follow my footsteps and have an engine failure it's not on me cuz I told yall the disclaimer 8~P
If your motor is precious to you use what is printed right there at the fill plug 10w40....
I also recommend you read your bikes owners manual recomendations though ;)

Any idea who supplies the oil for Suzuki? You might be able to find it at a lower cost with a regular supplier's name on the bottle.

That... is a very good question....
That I do not know... :hmm::shrug::???: :(

btw. clutch slippage unchanged so far. so that may have just been a coming issue months ago.