For the inexperienced gentlemen [ladies] on here,the first number,the 20 in this case,represents the viscosity [weight] of the oil when cold,[so it can flow thru the motor quicker [faster lubrication].The second number,the 40,,represents the weight of the oil once it reaches operating temperature so it will maintain a decent lubrication after the motor reaches its' operating temperature.
Myself,I don't use synthetic in ANYTHING I own,my bike included! Why?? Because there is no viscosity,atleast that I can feel when rubbing it between my fingers,cold or hot,not to mention,I was hearing strange metallic noises which are not good for any engine,especially when first started.
But with conventional dino oil,I can feel viscosity when rubbing it between my fingers,cold or hot,unlike with the synthetic stuff,meaning,it should have better lubrication qualities,plus,I do NOT hear those engine noises anymore.
And my understanding of the "WHY" synthetic oils were developed to begin with ,was for "EMMISSIONS" purposes,NOT superior lubrication.But whada I know?? I'm just a dumb Polock!!

Now,I'm NOT saying NOT TO USE the synthetic stuff,cause that's up to the individual!! Use whatever YOU feel is better for your particular application!!
And the dealerships HAVE TO USE it because that's what the factory requires em to use.And if they don't,they won't have a job for very long!! But once the vehicle is out of warantee,then all bets are off.