Ha ha... RON (Research Octane Level) is a measured comparison of the propensity of the fuel to auto-ignite on being compressed in the cylinder. If your engine compression ratio is such that 95 octane is not going to pre-ignite ('pinking') then running 99 RON fuel isn't going to buy you anything, except increased costs... That's all things being equal of course. Having said that, I've also also noticed that some fuels tend to experience pre-ignition in the blade at low RPM's. (e.g. 30mph in 2nd gear and you open the throttle wide). That's not dependent on 'advertised' RON though. I think some fuels are just crap.. H
