As mentioned Japans RON 90 would be about 85 octane to us.
90 RON isn't the same as 90 octane at the gas pump. It is calculated by the RON + MON/2 method RON might be what they use in Japan but it isn't the same. Straight RON numbers always run higher than RON + MON/2
RON 95/98 is the same as our RON + MON/2 91/93
We aren't running it because it is any kind of requirement of the engine. We run it because it is clean, consistent, non ethanol, leaded, low odor, inexpensive and run's like the dickens and it is readily available.
How many more reasons would one need to realize 100LL is an exceptional fuel for a little two strokes.
You would be hard pressed to find another fuel that compares except for some of the race fuels might but at 3 times the cost.
100LL is not 100 octane by the method used to rate pump gas. It is a MON rating not the RON + MON/2 rating used for auto pump fuel.
People tend to focus too much on what they have heard about running higher octane than you need makes less power and that lower octane fuel has more BTU's of energy than higher octane fuel and while this is true it would not be possible to measure the difference of having more octane than necessary in our engines. Having more octane than needed just doesn't mean jack to us whatsoever.
Look at the extreme octane difference of Colemans versus 100LL. Even though the engine will function on Colemans it will never make measurably more power with it than 100LL. It is probably going to perform a heck of a lot better with 100LL at almost 40 octane higher than the engine could be run on. This is extreme amounts of difference and it isn't measurable so running 100 instead of 90 sure as heck won't be any different.
Then the lead in 100LL is another benefit as it is a lubricating compound. Almost everyone racing 2 stroke motocross bikes are running leaded fuel. A lot run 100LL the rest leaded race fuel.
