(#2) Confused with fuel to use...

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NLS

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My manual clearly mentions that I should use "super unleaded" (I take it this means high octane fuel, i.e. more than 95), yet I see the general thread (esp. in my country) to be that 12GS just needs plain 95 octane unleaded.

I've heard stories from that "98 and 100 won't give you anything", to "100 will make your bike perform worse and even hurt it in the long run" (!). The manual seems to say that simple unleaded is not recommended. Is this a change in the 07 manual or something?

Or I am just confused?

(since I don't use the full performance of the bike yet - in my first 1700Km still - I haven't noticed performance differences, but I *think* I have noticed simple unleaded gives me a bit less range... I might be wrong though since "just once" is not a proper statistic)

So... what should I do?
 
there's a sticker on the tank of my 07 spec bike: superbleifrei/unleaded 95 RON
 
i normally use 95 with no problems. on occasion, i have used 98 RON with no discernible benefit.
 
this topic has been done to death on other forums (mainly for superbikes).

The simple answer is that RON rating doesnt affect performance, unless you have an adjustable ECU which can monitor the fuel rating and then tweak ignition advancing, air/fuel ratios etc accordingly. I.E. you have a fully automated and adjustable powercommander type device that is constantly achieving perfect fuel/air ratios.

The petrol itself does not give any higher calorific value between RON values. Therefore running 92 RON vs 95 RON will not mean that your bike is any more powerful/faster/fuel efficient etc.

All the RON value dictates is the point at which the fuel will ignite. If you have a bike that runs lower value RON fuel, you're more like to get pre-detonation/pinking/pre-ignition which is very very VERY bad for your motor.

This is affected by humidity, ambient engine temps, ambient air temps, fuel temp, air pressure (i.e. altitude) etc.

BMW engines are safe for use on as low as 91 RON fuels, but I wouldnt recommend it, as at higher altitude you'll get pre-detonation. (but then you may not have a choice).

You can also use leaded fuels, but it WILL destroy any cats in the exhaust.

Using anything more than 95 RON for normal day to day riding is just a waste of money, unless you've ubered your engine considerably, with superchargers, turbos, nitrous etc.
 
NLS, it's a German thing! 95 RON, which according to the manual is the reccommended fuel to use is called Super Unleaded in Germany, with 91 RON being called standard unleaded.
It is confusing and I've even filled up my old 1150GSA in Germany with 91 RON by mistake. The 1200GS's however can also apparently use 91 RON without any modifications or pinking problems.
Basically, 98 RON is not reccommended and 95 RON is the optimum choice! :)

Hopefully that makes it clearer for everyone!
 
bigchris said:
this topic has been done to death on other forums (mainly for superbikes).

The simple answer is that RON rating doesnt affect performance, unless you have an adjustable ECU which can monitor the fuel rating and then tweak ignition advancing, air/fuel ratios etc accordingly. I.E. you have a fully automated and adjustable powercommander type device that is constantly achieving perfect fuel/air ratios.

The petrol itself does not give any higher calorific value between RON values. Therefore running 92 RON vs 95 RON will not mean that your bike is any more powerful/faster/fuel efficient etc.

All the RON value dictates is the point at which the fuel will ignite. If you have a bike that runs lower value RON fuel, you're more like to get pre-detonation/pinking/pre-ignition which is very very VERY bad for your motor.

This is affected by humidity, ambient engine temps, ambient air temps, fuel temp, air pressure (i.e. altitude) etc.

BMW engines are safe for use on as low as 91 RON fuels, but I wouldnt recommend it, as at higher altitude you'll get pre-detonation. (but then you may not have a choice).

You can also use leaded fuels, but it WILL destroy any cats in the exhaust.

Using anything more than 95 RON for normal day to day riding is just a waste of money, unless you've ubered your engine considerably, with superchargers, turbos, nitrous etc.
Click to expand...

The 1200GS has lambda sensor, for fuel/air ratio adjustment and a knock sensor, temp measurement and an ecu that controls the spark timing and the injectors.

So in principle at least it ought to be able to optimise performance accordingly. If a higher RON fuel is used cannot the ecu adjust the fuel/air ratio and timing to get the max power without detonation? Would this be higher than when using a lower RON fuel where the ignition is retarded to avoid detonation? It obviously does make some adjustments but how much difference it makes to the performance as the fuel is changed I don't know. I would guess not much.

I believe that some of the other 1200 boxer engines (the sporty thing and the tourer) specify RON 98 for max performance but will run on 95 but make less power. I'm sure I read this in the BMW literature sometime ago.
 
Engineer said:
The 1200GS has lambda sensor, for fuel/air ratio adjustment and a knock sensor, temp measurement and an ecu that controls the spark timing and the injectors.

So in principle at least it ought to be able to optimise performance accordingly. If a higher RON fuel is used cannot the ecu adjust the fuel/air ratio and timing to get the max power without detonation? Would this be higher than when using a lower RON fuel where the ignition is retarded to avoid detonation? It obviously does make some adjustments but how much difference it makes to the performance as the fuel is changed I don't know. I would guess not much.

I believe that some of the other 1200 boxer engines (the sporty thing and the tourer) specify RON 98 for max performance but will run on 95 but make less power. I'm sure I read this in the BMW literature sometime ago.
Click to expand...

I think you'll find it's all to do with the compression ratio. As a rule of thumb as you up the compression ratio you can produce more power for any given engine. However as the compression ratio is increased the more susceptible the engine becomes to pre-ignition of the fuel in the compression stroke. To prevent this occurring it is necessary to use a fuel with a higher anti-knock rating which is what fuel of a higher - i.e 98ron -octane rating. Think you'll find, but I haven't checked, that the r1200s has a higher comp ratio than the gs. It can therefore produce more power but this is dependent on using the 98 ron fuel - otherwise you'd get lots of pre-ignition with the risk of serious engine damage. However BMW being the clever folks have also designed the 1200s to be able to run on 95ron fuel by fitting antiknock sensors to the cylinder heads. These will retard the ignition the ignition timing but with effect of also reducing the power.

For the gs things are slightly different as it has a lower compression engine anyway, which as a rule of thumb normally translates to softer power delivery but with less peak power. Because of the lower compression it 'only' needs 95ron fuel, and can also compensate via the anti knock sensors for fuel of a lower octance rating. However putting fuel in of a higher rating wont produce any more power as it will already be running at its designed optimum already and advancing the ignition timing (to make use of the anti knock capabilities of 98ron fuel) would not produce any increase in power output. In fact the only measurable effect of putting 98ron into a GS would be to drain your wallet more quickly. :)

Peter
 
anyway what I know is that my bike performes smoothly with both kinds of fuel

but IF 98 (or 100) gives a bit better mileage, then my pretty basic brain tells me that something must be working a bit better
 
NLS said:
anyway what I know is that my bike performes smoothly with both kinds of fuel

but IF 98 (or 100) gives a bit better mileage, then my pretty basic brain tells me that something must be working a bit better
Click to expand...

You may find that the better mileage is more attributable to the fact that your bike is still loosening up - after all, it's only done 1700Km
 
could be

though I think I remember the same with my 650GS Dakar (!)

maybe it is another thing... plain unleaded is more messed up (by the shop) than super unleaded :)
 
Steve said:
I think it's purely a naming convention. On the continent, "super unleaded" is 95 ron, the same as our normal unleaded.
Click to expand...

I'm not surprised people get confused. Our UK "normal" 95RON unleaded is called "premium" on the pumps.

The GS12 I rented in California had a sticker on the tank stating that 89 octane should be used. But, of course, they're different in California. Probably.
 
ampthill said:
I think you'll find it's all to do with the compression ratio. As a rule of thumb as you up the compression ratio you can produce more power for any given engine. However as the compression ratio is increased the more susceptible the engine becomes to pre-ignition of the fuel in the compression stroke. To prevent this occurring it is necessary to use a fuel with a higher anti-knock rating which is what fuel of a higher - i.e 98ron -octane rating. Think you'll find, but I haven't checked, that the r1200s has a higher comp ratio than the gs. It can therefore produce more power but this is dependent on using the 98 ron fuel - otherwise you'd get lots of pre-ignition with the risk of serious engine damage. However BMW being the clever folks have also designed the 1200s to be able to run on 95ron fuel by fitting antiknock sensors to the cylinder heads. These will retard the ignition the ignition timing but with effect of also reducing the power.

For the gs things are slightly different as it has a lower compression engine anyway, which as a rule of thumb normally translates to softer power delivery but with less peak power. Because of the lower compression it 'only' needs 95ron fuel, and can also compensate via the anti knock sensors for fuel of a lower octance rating. However putting fuel in of a higher rating wont produce any more power as it will already be running at its designed optimum already and advancing the ignition timing (to make use of the anti knock capabilities of 98ron fuel) would not produce any increase in power output. In fact the only measurable effect of putting 98ron into a GS would be to drain your wallet more quickly. :)

Peter
Click to expand...

Yes - I was also going add something about compression ratio but it was starting to get a bit long-winded so left that for others to fill in. :-)
 
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