Premium – Regular & the Octane Story Part 2

Following on from Premium – Regular & the Octane Story Part 1 where the importance of using the right grade of fuel were explained, it’s also important to understand that there are differences in fuel formulas and how fuel grades are identified, depending on where they are sold.

There are two things to consider that are far more important than names such as Premium, Ultimate, Power, Super,  etc.  The first is the octane rating and the second is whether or not the fuel is blended with ethanol.  In this article we will deal with specifically octane ratings and how you can determine exactly which grades of fuel sold in your county are suitable for your bike or scooter.

There are two main scales used to rate fuel octane.  The most commonly used is the RON scale.  RON stands for Research Octane Number.  The test used for this scale is best suited to rate fuel used in normal road vehicles.

The other rating scale is the MON scale which stands for Motor Octane Number.  This scale is used in motor sport and aviation and is specifically designed to rate fuel for engine conditions at higher loads.

In most cases, commercially available fuel has been rated for both these scales by the testing agency and the MON will be typically 8 - 12 points lower than the RON rating.  It is not possible to reliably convert between the two scales as commercial fuels differ widely and the difference in the rated number will be higher or lower depending in the actual fuel formula.

The important thing for bike and scooter owners is knowing what octane rating is recommended for their bike or scooter and which scale has been used to specify it.  The next thing is then to match that with the fuel available in your country.

Most countries use the RON scale to specify the octane rating of fuel sold at commercial outlets.  These include all of Europe, the UK, Ireland, the Middle East, South Africa, Asia, Australia , New Zealand, most South American and some Central American countries.  In these countries 95 Octane fuel for example is 95 RON if not already specified at the outlet.

In some other parts of the world the rating system and display at the outlet is quite different however.  Canada, the USA, Mexico, Brazil, and possibly some other Central and South American countries use an average of the RON and MON which they call the AKI and which stands for “Anti Knock Index”.  At some outlets in these countries it is labelled on pumps as (R+M)/2 or by another designation POM which stands for “Pump Octane Number”.  This causes a lot of confusion for owners in these countries and also for readers of on-line forums when they are getting what seems to be contradictory “advice” from other owners about what fuel to use.

The Italian manufacturers are careful to specify the grade of fuel required and this will be detailed in the Owner’s Manuals or other technical documentation.  Fuel ratings will be in RON as this is the European standard however in some cases both RON (sometimes written NORM) and MON (sometimes written NOMM) ratings are given.  Bikes and scooters specifically for the US and Canadian market may also have fuel recommendations listed in the documentation by the (R+M)/2 method as is used in their area.

The table below shows a comparison between RON, MON and AKI with examples of some fuels in different markets.  There are however regional variations in a lot of countries so it is always best to find out the actual octane rating of the fuel you are buying rather than rely on the description.   Ratings for the reference compounds n-heptane and iso-octane as well as straight ethanol and methanol are also shown for general interest.

FUEL	RON	MON	AKI
Standard Unleaded – Europe, UK, Ireland, RSA	95	85
High Octane Premium Unleaded – Europe, UK, Ireland	102 - 97	88
Standard Unleaded  - USA, CDN	91 - 92	82	87
High Octane Premium Unleaded - USA, CDN	98 - 97	88	94
Standard Unleaded  - AUS, NZL, RSA, Asia, Mid East	91 - 92	82
Premium Unleaded  - AUS, NZL, RSA, Asia, Mid East	95	85
High Octane Premium Unleaded - AUS, NZL, RSA, Asia, Mid East	100 - 97	88
n-Heptane	0	0	0
Iso-Octane	100	100	100
Ethanol	108	90
Methanol	109	89