Octane confusion

[brumbackkid]

This has probably been beaten to death. On my new to me 08 GS the manual called for 95 ronzon fuel, which I assume is octane. Can I get some feedback on the average grade of fuel the GS likes? In my area 95 octane is unobtainum.

[MotoGP]

They'll run on most any grade fuel pretty well. Can't find greater than 91 octane in my area but I have used 87-89 with no issues. Just use the highest octane available and you'll be ok

[marc]

Where are you? It makes a difference because there are three kinds of octane readings and what you see on the pump may be different than what you read in the manual even though the gas is the same.

The most common way of measuring octane in the world is called Research Octane Number (RON). That is the number you are probably seeing in your book. There is also the Motor Octane Number (MON) which better measures how fuel behaves under load (according to wikipedia). But it's a smaller number. In the US pump octane is reported as the AKI or Anti Knock Index, sometimes called the Pump Octane Number (PON). It is calculated as (RON + MON) / 2.

The MON is typically 10~12 numbers lower than the RON which makes the AKI about 5~6 numbers lower than the RON. So if the book says 95 RON is required an AKI of 89~90 is about right.

My tank has a sticker around the fuel fill opening that specifies fuel with an AKI of 89 or higher. If I take the bike to a place that used RON on the pump I'll look for a RON of 94~95 or higher.

[multiplu]

Nothing to be confused about,its simole

put the cheap crappy low grade in then go and put good stuff from Shell or Mobil in

its like night and day!

[brumbackkid]

Originally Posted by marc

Where are you? It makes a difference because there are three kinds of octane readings and what you see on the pump may be different than what you read in the manual even though the gas is the same.

The most common way of measuring octane in the world is called Research Octane Number (RON). That is the number you are probably seeing in your book. There is also the Motor Octane Number (MON) which better measures how fuel behaves under load (according to wikipedia). But it's a smaller number. In the US pump octane is reported as the AKI or Anti Knock Index, sometimes called the Pump Octane Number (PON). It is calculated as (RON + MON) / 2.

The MON is typically 10~12 numbers lower than the RON which makes the AKI about 5~6 numbers lower than the RON. So if the book says 95 RON is required an AKI of 89~90 is about right.

My tank has a sticker around the fuel fill opening that specifies fuel with an AKI of 89 or higher. If I take the bike to a place that used RON on the pump I'll look for a RON of 94~95 or higher.

I live in Southern Idaho. High Test is about 91 at the pump these days. I had a engineer friend tell me the lower the octant as long a the engine did not piong...actually had better burn...any truth to that theory?

[marc]

There is some truth to the theory. In used to be the thing to do. Today it's not so simple because engine control systems are smarter. If the bike starts knocking engine management will retard the timing to stop the knocking. That lets you use lower octane fuel at the cost of fuel efficiency and therefore possibly lower MPG.

91 pump octane in the US is about 96 RON. I get no noticeable mileage changes between 89 AKI and 91 AKI so use the recommended 89. I don't worry about the times that the only gas available is 87 (Stovepipe Wells, Death Valley, for example).

[brumbackkid]

Originally Posted by marc

There is some truth to the theory. In used to be the thing to do. Today it's not so simple because engine control systems are smarter. If the bike starts knocking engine management will retard the timing to stop the knocking. That lets you use lower octane fuel at the cost of fuel efficiency and therefore possibly lower MPG.

91 pump octane in the US is about 96 RON. I get no noticeable mileage changes between 89 AKI and 91 AKI so use the recommended 89. I don't worry about the times that the only gas available is 87 (Stovepipe Wells, Death Valley, for example).

Yes...3/4 of Northern BC and the territories have no designation on the pump...who know what is going in the tanks. At Eagle Plains you just thank god for the opportunity to buy fuel.