{"id":594,"date":"2019-02-14T16:44:13","date_gmt":"2019-02-14T16:44:13","guid":{"rendered":"https:\/\/bmwmotorcycles.local\/news_rss\/understanding-octane-aki-mon-and-ron-oh-my\/"},"modified":"2025-03-30T21:16:11","modified_gmt":"2025-03-31T01:16:11","slug":"understanding-octane-aki-mon-and-ron-oh-my-2","status":"publish","type":"post","link":"https:\/\/bmwmoa.org\/understanding-octane-aki-mon-and-ron-oh-my-2\/","title":{"rendered":"Understanding octane \u2013 AKI, MON and RON, oh my!"},"content":{"rendered":"<p>I\u2019m as excited about the new F 750 and 850 bikes as just about anybody who loves to look at new motorcycles but isn\u2019t going to buy one of those because they\u2019ve got their eye on a different bike already,  and by \u201ceye on,\u201d I mean \u201cdeposit paid.\u201d Paul Guillien, MOA member, dedicated off-road rider and oh by the way, CEO of Touratech USA, did a great job whetting my appetite for the next generation of BMW\u2019s parallel twins with videos on YouTube and a <a href=\"http:\/\/bmwmoa.org\/news\/432004\/Late-but-worth-the-wait-The-BMW-F-850-GS-finally-arrives.htm\" target=\"_new\" rel=\"noopener\">great article in <em>BMW Owners News<\/em><\/a>.\n<\/p>\n<p>When I got to the tech specs of the new bikes, I noticed something and thought, \u201cHey, I\u2019m a pretty tech-aware guy, and if this confuses me, maybe there are other people who wonder about this as well.\u201d I am referring to the part of the specs where BMW recommends what kind of gasoline should be used for the bike. In this instance (and you can refer back page 69 of the January issue to see what I\u2019m talking about) the F 750 GS spec is for 91 RON gas, while the F 850 GS is rated for 95 RON fuel. The spec sheet calls 91 RON \u201cregular\u201d and 95 RON \u201cpremium,\u201d but most of us reading this magazine don\u2019t see 91 next to \u201cregular\u201d on the gas pumps we use.\n<\/p>\n<p>Perhaps the confusion stems in part from not knowing that when you read the tech specs for a BMW motorcycle, BMW is referring to the sticker on the pump in Germany. The good news is that at its most basic level, regular gas is regular gas, and 91 RON in Germany is equivalent to 87 AKI in the United States. Premium is the same, and while premium gasoline is often called \u201csuper\u201d by some retailers, 95 RON in Germany is equivalent to 91 AKI in the USA and Canada. What they call \u201csuper plus\u201d in Germany in 98 RON, or 93 AKI stateside.\n<\/p>\n<p><img decoding=\"async\" class=\"lazyload\" alt=\"\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"http:\/\/bmwmoa.org\/resource\/resmgr\/tech\/19-01_octane\/gaspump.jpg\" \/><noscript><img decoding=\"async\" class=\"lazyload\" alt=\"\" src=\"http:\/\/bmwmoa.org\/resource\/resmgr\/tech\/19-01_octane\/gaspump.jpg\" \/><\/noscript>\n<\/p>\n<p>You can stop reading right there and take away a couple of things. First is the knowledge that regular means regular and premium means premium (or super), and if that\u2019s all you remember when it comes to your motorcycle, you\u2019re fine. The second is nobody really bothers specifying those mid-grade fuels, so in general you can just skip them unless they\u2019re your only choice for some reason.\n<\/p>\n<p>On U.S. and Canadian pumps, you\u2019re generally presented with three choices: 87, 89 and 93. Some stations throw in 88, 91 or even 95. We think of gasoline as the go juice for our motorcycles, but there\u2019s more to it than just suck, squish, boom, blow, especially when it comes to the amazing technology built into our modern motorcycles. In the old days when one twist grip was the throttle and the other advanced the timing, the rider had to have a feel for what was going on with the bike at all times. Fuel injection and computers have taken that need from us, thankfully, but that doesn\u2019t mean we can\u2019t understand what\u2019s going on.\n<\/p>\n<p>The abbreviations we see used to describe the quality of gasoline are varied, but luckily there are only a few of them.\n<\/p>\n<ul>\n<li>RON: Research Octane Number, used in Europe and most other places in the world\n    <\/li>\n<li>MON: Motor Octane Number, usually accompanies RON\n    <\/li>\n<li>AKI: Anti-Knock Index, used in Brazil, Canada, the U.S. and a few other countries\n    <\/li>\n<li>RdON: Observed Road Octane Number, not seen on pumps\n    <\/li>\n<\/ul>\n<p>\nThe RON of a particular blend of gasoline is determined by scientists and engineers who run the gas through a test engine at 600 RPM under tightly controlled conditions. The engine itself is special, because unlike your motorcycle, the compression ratio of the engine can be altered on the fly. MON is determined at 900 RPM using fuel that\u2019s been warmed up, and the special engines used for MON testing have variable ignition timing on them.<\/p>\n<p>AKI isn\u2019t determined by testing, but rather by mathematics. You take the RON, add the MON to it, then divide the sum by two. You may recognize the formula (R + M)\/2 as what we commonly refer to as an average, and you\u2019d be right. Where MON is usually 8 to 12 numbers below RON, AKI is usually 4 to 6 numbers below RON, right about in the middle between MON and RON.<\/p>\n<p>The K in AKI stands for Knock, and you don\u2019t want your engine to knock. When an engine knocks, that means the air-fuel mixture in the cylinders is burning unevenly or incompletely, neither of which is good for your engine. While there are other things that can cause knocking, such as worn out spark plugs or excessive carbon deposits in the cylinders, we\u2019re talking about octane here, so that\u2019s what we\u2019re going to focus on. (Maintenance note: if two or three tanks of the proper AKI-rated gasoline don\u2019t eliminate your engine knocking problems, put in new spark plugs.)\n<\/p>\n<p><img decoding=\"async\" class=\"lazyload\" alt=\"\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"http:\/\/bmwmoa.org\/resource\/resmgr\/tech\/19-01_octane\/knocksensor.jpg\" \/><noscript><img decoding=\"async\" class=\"lazyload\" alt=\"\" src=\"http:\/\/bmwmoa.org\/resource\/resmgr\/tech\/19-01_octane\/knocksensor.jpg\" \/><\/noscript><br \/>\n<span style=\"font-size: 12px;\"><em>Knock sensor illustration from <a href=\"https:\/\/www.azosensors.com\/article.aspx?ArticleID=50\" target=\"_new\" rel=\"noopener\">AZO Sensors<\/a><\/em>.<\/span>\n<\/p>\n<p>Here\u2019s the important part: gasoline with a higher AKI (or RON or MON) can withstand more compression at a given temperature before it ignites. High performance engines with high compression require high AKI gasoline, it\u2019s that simple. You might save a little money by putting 87 in your engine that requires 91, but over time you\u2019re not doing yourself any favors by introducing increased wear and poorer performance to your motorcycle engine.\n<\/p>\n<p>At the gas station closest to my house (at the time of this writing (mid-December 2018), 87 AKI gas costs $1.99 per gallon and 93 AKI costs $2.89 per gallon, a difference of 90 cents a gallon. My 2005 R 1200 GS holds 5.3 gallons of fuel, so filling a completely dry tank would cost me $10.55 with 87 and $15.32 with 93. Filling my tank with 93 therefore costs me $4.77 over filling it with 87.\n<\/p>\n<p><img decoding=\"async\" class=\"lazyload\" alt=\"\" src=\"data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\" data-src=\"http:\/\/bmwmoa.org\/resource\/resmgr\/tech\/19-01_octane\/coins.jpg\" \/><noscript><img decoding=\"async\" class=\"lazyload\" alt=\"\" src=\"http:\/\/bmwmoa.org\/resource\/resmgr\/tech\/19-01_octane\/coins.jpg\" \/><\/noscript>\n<\/p>\n<p>The compression ratio of my engine is 11.0:1, and BMW specifies the use of 95 RON gasoline \u2013 91 AKI. Since my nearest gas station doesn\u2019t sell 91, it\u2019s better to go over (93) than under (89). Having said that, one of the great things about the GS platform is that BMW intends them to be ridden anywhere at any time, and incorporates whiz-bang computer programming called Automatic Knock Control to enable cheapskates all over the world to use 91 RON (87 AKI) gasoline.\n<\/p>\n<p>Automatic knock control is typical for automotive engine management systems, and it\u2019s becoming increasingly pervasive in motorcycles. Its function is simple: when the sensors detect knocking, the bike\u2019s computers delay the introduction of the spark into the cylinder. This gives the piston an extra split second to compress the fuel-air mixture to the correct level. Due to the process of four-stroke internal combustion, this means that the piston is likely on its down stroke when the knock-retarded ignition takes place. This robs you, the rider, of power and decreases fuel efficiency over time.\n<\/p>\n<p>One of the problems with engine knock is that by the time you actually hear it, the damage is done. Engine knock sounds occur around 6-8 kHz, which is in the middle of humans\u2019 hearing range, but they\u2019re not typically loud sounds until you really have a problem. You\u2019re more likely to feel knocking through your butt, hands and feet before you hear it. Once it gets bad enough to be audible, you could be looking at serious engine problems.\n<\/p>\n<p>The way to prevent knock, then, is to use fuel with an appropriate octane rating for the compression ratio of the cylinders. This comes down to math yet again, but it\u2019s easy math if you have the data. Find out the volume of the cylinder with the piston at bottom dead center and compare that to the volume of the cylinder with the piston at top dead center; the resulting ratio represents what kind of gas you need to run in your bike for peak performance. An engine with a high compression ratio, as is the case with the above-mentioned F 850 GS, requires higher octane gasoline than an engine with a low compression ratio.\n<\/p>\n<p>Determining the volume is a little more complicated, math-wise. You have to know the bore and stroke of the cylinder, the compression height of the piston as well as its dome height (or dish depth), the piston-to-deck clearance (bore squared x 0.7854 x distance between piston and deck at TDC), and even the thickness and bore of the head gasket. Then and only then can you run the formula through to determine the compression ratio. This is perhaps why we take the manufacturer\u2019s word for it when it comes to compression ratios.\n<\/p>\n<p>Here\u2019s where the monkey gets the wrench, though. Because of any number of myths and a certain level of ignorance as to how gasoline and internal-combustion engines function, many riders believe that putting premium gas into an engine with a low compression ratio will boost performance. It simply will not. Premium gas is not better gas than regular gas, it simply has higher octane to be suited for engines with a high compression ratio. As far as your low-compression-ratio-engine is concerned, the excess octane beyond what it requires is wasted, which means the extra 30 cents a gallon you spent on that 93-octane fuel when your bike only needs 87 became dust in the wind. Unless, of course, your engine is pinging and knocking. In that case, try buying a couple tanks of gas one octane rating higher than usual and see if that takes care of the noise. If it does, it\u2019s time for a tune-up, because something is out of spec with your engine. If going up one grade of gasoline doesn\u2019t work (or isn\u2019t possible), you may need to consult a qualified motorcycle mechanic.\n<\/p>\n<p>In the end, Super and Premium are words used by marketing experts to trick you into buying gas you think is better for your car or motorcycle rather than Regular or Mid-Grade. After all, you\u2019re special, so your motorcycle must be special too, right? Problem is, unless you\u2019ve got an absolute ton of money, your bike isn\u2019t special. Certainly your 2007 R 1200 RT isn\u2019t special, and there isn\u2019t a gallon of 98 octane fuel anywhere in the world that\u2019s going to improve the performance curve of your bike.\n<\/p>\n<hr \/>\n<p><i>Read Part Two of this series on fuel and fueling at <a href=\"http:\/\/bmwmoa.org\/news\/444409\/\" target=\"_new\" rel=\"noopener\">C2H2OH: Ethanol<\/a>.<\/i><\/p>\n","protected":false},"excerpt":{"rendered":"<p>I\u2019m as excited about the new F 750 and 850 bikes as just about anybody who loves to look at new motorcycles but isn\u2019t going to buy one of those because they\u2019ve got their eye on a different bike already, and by \u201ceye on,\u201d I mean \u201cdeposit paid.\u201d Paul Guillien, MOA member, dedicated off-road rider [&hellip;]<\/p>\n","protected":false},"author":9,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[73],"tags":[],"class_list":["post-594","post","type-post","status-publish","format-standard","hentry","category-moa-garage"],"acf":[],"_links":{"self":[{"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/posts\/594","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/users\/9"}],"replies":[{"embeddable":true,"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/comments?post=594"}],"version-history":[{"count":0,"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/posts\/594\/revisions"}],"wp:attachment":[{"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/media?parent=594"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/categories?post=594"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bmwmoa.org\/wp-json\/wp\/v2\/tags?post=594"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}