whats the difference between RON and MON when it comes to fuel specs?

Just different ways of determining the octane...the measurement of MON rating is more sensitive to operating conditions...

Rob.

If you look at the bottom of this webpage it's got some stuff...

Rob.

RON measures the octane rating of a fuel under light load. MON measures its octane rating under a heavier load. MON is (almost) always lower than RON.

The "sensitivity" of a fuel (i.e. the difference between RON and MON) is just as important as its absolute RON rating - a 98RON/88MON fuel (high sensitivity) would be worse for "real world" use than a lower sensitivity 96RON/91MON fuel.

American gas pumps show the Anti Knock Index, which is an average of RON and MON; i.e. (R + M) /2.

THIS site goes into more detail.

so the higher the mon the better the fuel?

...with relation to the difference with the RON...

Rob.

so the higher the mon the better the fuel?

Apparently so, for racing:- http://www.osbornauto.com/racing/octane.htm