RON MON and other boring stuff
This is just some info to shed some light on why Europes (sorry to include non-US in the European category - but the calulations are the same). This is why most non-US target bikes demand such high octane fuels - they really dont...
Careful on this: The rating method for fuels in Europe is different than
what you see posted on US pumps. EU uses the RON which is usually Higher
than the MON or [(RON+MON) / 2] you see posted on US pumps. If you do the
math a RON of 91 is roughly the same as the [(RON+MON) / 2] rating of 93
you typically see on the US pumps.
MON stands for Motor Octane Number, and RON for Research Octane Number.
They are both arrived at through different experimental means, and do not
have a direct linear relationship to each other, though it is close.
In the US, the gasoline stations post the commonly called "Road" Octane
Number, or [(RON+MON) / 2]. MON is always lower than RON, so that is why
our octane levels may *seem* low, when in fact the different grades between
the US and Europe are very likely the same or very similar.
As consumers, we use the pump octane and manufacturers recommendation to
determine which gasoline to buy. Octane is a general term used to indicated
a gasoline's ability to resist engine knock. The pump octane is also
referred to as the Anti-Knock Index (AKI). AKI is determined based on an
average of the Research Octane Number (RON) and the Motor Octane Number
(MON). The formula is RON+MON/2 normally abbreviated as R+M/2 on the pump.
Octane is tested in a single cylinder octane test engine. The MON is a
measure of the gasoline's ability to resist knock under sever operating
conditions. MON affects high speed, part throttle and performance (under
load such as in passing). The RON on the other hand, is a measure of
gasoline's ability to resist knock under less sever conditions. RON affects
low to medium speed knock and engine run-on (dieseling). For a given AKI,
RON is typically 8-10 points higher than the MON. As an example, 87 AKI
(pump octane) fuel would have a MON of 82 and a RON of 92.
What your engine requires to operate knock-free, is referred to as the
Octane Number Requirement (ONR). The ONR for an engine is affected by design
factors and real world conditions. Engineers must balance performance,
economy and environmental concerns in their design. Compression ratio,
ignition timing, air/fuel ratios, temperatures and combustion chamber design
all have an affect on the ONR. Compression ratio has the most significant
impact on the ONR and engine efficiency. The higher the compression ratio,
the higher the ONR and combustion efficiency. Retarded timing, rich or lean
air/fuel ratios, lower combustion temperatures and high swirl combustion
chambers all work to reduce an engine's ONR.
In the real world, there are other factors that affect these designs
including barometric pressure, temperature and humidity. Increases in
barometric pressure or temperature, increase the ONR. Increases in humidity
or altitude (lower barometric pressure), reduces the ONR. Combustion chamber
deposits increase temperature and compression thereby increasing the ONR.