when i bought my 500(new sept.99), i ran 32:1 and fouled plugs like crazy. now i run motul 800 @ 40:1 and haven't had any problems. i run my bike hard in the deserts of so cal, and i'm still on my stock piston and rings. pulled the cylinder off this summer, just to have a look, everything still looked good. my motto...if it ain't broke, don't fix it. like the above thread said, you'll be told everything from 32:1 to 100:1. just my 2 cents, 40:1 with a quality oil and you'll be fine....the 500 is a bullet-proof motor.