I just got a 98 gsr and I'm determining which oil I'm better to use. Synthetic or not and how much kilometers before I change it... The only thing I know about synthetic oils is how good it is for 2 strokes premix engine. I have a atc 250r and I always use synthetic oil. The smell is fu"$$ so cool (klotz super techniplate 20$ castor oil). Normal oil (like castrol 2 stroke petroleum based) mixed at 24:1 = 50:1 (synthetic oil like klotz...). And I'm sure than even at 50:1 it protects my engine more than petroleum at 24:1. So maybe synthetic oil in a car can do miracle on engine wear, gas mileage or power, ...? Still looking for the answer. The old owner was using quaker 5w30 non synthetic so I'll use it until I know a greater oil.