Octane: What It Is and What It Means to You - Adventure Rider (2024)

According to the Cambridge Dictionary, “High-octane fuel is of very good quality.” While this oversimplified definition is not incorrect, it does not accurately define the difference between low and high-octane fuel, leaving the reader with the misconception that higher octane is always better. It may well be worth running premium fuel in your BMW R 1300 GS Adventure, but will your adventure tractor Kawasaki KLR650 benefit? Read on to learn the truth about octane ratings and whether running high-octane gas is right for you.

What Is Octane, Anyway?

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Photo: Justin Hughes

Contrary to popular belief, an octane rating is not a direct indication of a particular blend of fuel’s overall quality. According to the EPA, “Octane rating is the measure of a fuel’s ability to resist ‘knocking’ or ‘pinging’ during combustion, caused by the air/fuel mixture detonating prematurely in the engine.” That’s it. Every other label you see on premium gas, the “V-Power Nitro+ Wicked Mega Awesome” grade, is marketing hype intended to make you spend more money on a higher grade of fuel that you may or may not need.

In North America, gas is typically available in three varieties: regular, mid-grade, and premium. The numbers that appear on the pump can vary depending on the method used to calculate them. In North America, we use what is known as the (R+M)/2 method. You might have seen this formula printed on the pump, as shown in the picture above. We use two tests to determine the octane number. The research octane number (RON) is tested under engine idle conditions with a low air temperature and slow engine speed. The motor octane number (MON) is tested under the more stressful conditions of higher air temperature and engine speed. The number you see on the pump is the numbers derived from each of these tests added together and then divided by two to get an average. The (R+M)/2 formula means RON plus MON divided by two.If you want to seriously nerd out on how these ratings are measured and exactly what the difference is between fuels, the U.S. Energy Information Administration goes into great detail about this. For our purposes, it’s safe to say that typically, regular gas is 87 octane, mid-grade is 89, and premium is 91 or 93.

It’s important to note that in Europe and elsewhere in the world, only the RON number is used to derive octane ratings, which is typically higher than the (R+M)/2 number we see on pumps in North America. However, the standard grades of regular (90), mid-grade (92), and premium (95 or 96) are comparable to what’s available here. A 90 RON fuel is no better than our 87 despite the higher numerical value.

What Octane Should I Use?

This is not to say that you should just run regular gas no matter what, however. Manufacturers are trying to achieve as much fuel efficiency, power, and low emissions as possible these days. The sophisticated engine management systems of many modern motorcycles can often do this by pushing air/fuel mixtures a bit closer to the limits than carburetors or more basic fuel injection systems. This means a greater chance of pre-ignition, on purpose, in the name of better and cleaner performance. The best way to mitigate the chance of knocking is by requiring a higher-octane fuel and tuning the engine management system to work with its more knock-resistant capabilities. My Subaru WRX required premium for these reasons, plus the addition of turbocharging to cram even more air into the engine to add more fuel and make even more power.

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Photo: BMW

The BMW R 1300 GS Adventure mentioned above is one such motorcycle, and as a result, it requires premium fuel. Though not turbocharged, it is still a finely tuned high-performance engine, so only the top-tier fuel is acceptable. Its knock sensors and other electronics will try to save you from yourself if you run lower-grade fuel than recommended. This is not good for the engine, however, reducing performance and potentially leading to engine damage in extreme cases. Before you buy the BMW, know that you’re going to have to splurge for premium fuel as well. Not to single out BMW, this is the case for many other high-performance motorcycles as well.

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Photo: Justin Hughes

However, not all new, fuel-injected motorcycles require premium. Take my significant other’s 2024 Kawasaki KLR650S, for example. I checked her owner’s manual, and Kawasaki still requires a minimum of 87 octane. Plain ordinary regular gas is perfectly fine, despite the third generation’s switch from carburetion to fuel injection. No doubt this is partly because the KLR’s engine design hasn’t changed much since its introduction in 1987. Its fuel injection system literally bolts onto the side of the engine in place of the old carburetor, a clear indication of making as few changes to the old design as possible while still meeting modern emission requirements.

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Photo: Justin Hughes

It doesn’t have to be an older design to run regular gas, though. Unlike the KLR, my Suzuki V-Strom 650 was designed in the 21st century, yet it, too, requires only 87 octane fuel. The V-Strom was never carbureted, and its fuel injection system was optimized for regular, not premium.

The definitive answer as to what fuel you should run in your bike is to run whatever your manufacturer recommends. I can get away with regular in my fleet, but BMW has good reasons to require premium. Check the owner’s manual for your specific make, model, and year, and follow those instructions. If you don’t have a copy of your manual with your bike, you should be able to look it up online. Be careful to follow the manufacturer’s actual recommendation, though, and not some wild speculation from the forums.

Also, it is true that some petroleum companies add extra detergents and additives to their premium grades, above and beyond what is required, and these can have favorable effects on your engine. If you want to reap the benefits of these additives but your bike only requires regular gas, go ahead and run a tank of premium every once in a while. You will never harm an engine by running a higher octane grade than you need to. You also will not benefit from additional power or performance unless the engine is specifically tuned to take advantage of this fuel. But if you like the idea of running premium’s extra additives through your engine once in a while, go right ahead.

What If I Can’t Get High Enough Octane Fuel?

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Photo: Justin Hughes

Unfortunately, especially if your bike legitimately requires premium fuel, you may find yourself in a situation where that fuel is not available from the pump. I ran into this myself while exploring Colorado in August 2022. Once at high elevations, regular was 85 octane, mid-grade was 87, and premium was 91. What was I to do?

Again, from the EPA: “The sale of 85 octane fuel was originally allowed in high-elevation regions—where the barometric pressure is lower—because it was cheaper and because most carbureted engines tolerated it fairly well. This is not true for modern gasoline engines. So, unless you have an older vehicle with acarbureted engine, you should use the manufacturer-recommended fuel for your vehicle, even where 85 octane fuel is available.” Indeed, I had no problem running 85 octane in my 2005 KLR650. It was a carbureted model, and it ran the lower octane fuel just fine, just like the EPA said it would. However, my camper van was fuel-injected and required at least 87 octane, so I had to splurge for “mid-grade” to get the required octane rating. I don’t know why 85 octane fuel is still permitted against EPA recommendations, especially now that nearly every vehicle on the road has fuel injection.

What if I had a highly tuned engine that required 93 octane, which wasn’t even available? One option would be to add octane booster, which is typically available at gas stations. Be sure to follow the instructions on the bottle to ensure the correct mixture of booster with the amount of fuel in your tank. Another option may be possible if you have an aftermarket tuning device of some kind. For example, on my Subaru WRX, my COBB Accessport offered performance tunes for both 93 and 91 octane fuel. I typically ran the tune for 93, which was widely available in my home at the time of Massachusetts. When I visited Maine, however, I switched to the 91 tune since that’s typically the top fuel you can find there. I gave up a few horsepower (which I didn’t even notice), but I kept my engine safe.

What If I’m In the Middle of Nowhere?

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Photo: VIA TMFF

Of course, as adventure riders, we may find ourselves in far off places with extremely limited access to fuel of any kind, never mind the proper octane rating. Sometimes, beggars can’t be choosers. What do you do then? I’ve never experienced this myself, so I asked someone who has, author and motorcycle adventure traveler Sam Manicom.

“Low octane was often all that was available,” said Sam. “Egypt and Pakistan are two examples. The bike pinged like crazy with the poor fuel and heat, and that was even with compression plates in the cylinders!” According to Ferriday Engineering, compression plates, or in this case decompression plates, are “a solid metal copy of a head gasket and can be used as well as one conventional head gasket to lower the compression ratio of a[n]… engine without compromising piston strength.” Think of it like a spacer between the engine block and the head(s), slightly enlarging the cylinder(s) and reducing the compression ratio, which in turn reduces the chance of knocking. While this is an extreme measure, it may be worth considering if you regularly ride in areas with poor fuel quality.

How did Sam deal with these poor running issues? “I had to let the bike cool off from time to time in heavy, slow traffic,” he said. “I also had to open the throttle much more gently, accelerating away from traffic lights and more gentle overtaking, too. All was good, but that was on my 1992 BMW R80GS. I’m no help on newer bikes, I’m afraid.”

Oh, yes, you are. Those same techniques will also be helpful on newer fuel-injected bikes. Their electronics will also detect engine knocking and change the air/fuel mixture to avoid it, though at the cost of performance. It’s not good to run lower octane fuel than recommended, but if you absolutely have to, try to keep the engine load and RPMs as low as possible. Basically, don’t ask too much of the engine until you can get the proper grade fuel in the tank.

Octane: What It Is and What It Means to You - Adventure Rider (2024)
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