The octane number displayed at gas stations is an average of RON and MON (Ron + Mon / 2).
RON is measured under mild conditions and is more important in controlling part throttle knock. If an engine is pinging at part throttle it needs more RON .
MON is measured under more severe conditions, and as a result, the number is lower than for the mildly-tested Ron. If an engine is detonating at wide open throttle a higher MON is required. MON is the most important number for race engines. Higher octane does not mean more power, unless the engine is experiencing detonation.