I have a 2005 Sporty 1200c and have read many, many threads on what oil to use. I have a pretty good handle on the better brands but I'm confused about the viscosity. It seem that 20-50 synthetic is the most recommended but my service/repair manual recommends SAE 20-50 above 40 degrees, SAE 50 above 60, and SAE 60 above 80. I haven't seen these heavier weights talked about. So, what's the real scoop on summer riding with temps over 80? Or, will 20-50 synthetic cover all the bases?