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I've inadvertently opened a can of worms on another forum I frequent by mentioning that I use nothing but premium fuel (91 octane here in Canada) in my bikes. The owner's manual on my current and each of my last three bikes have all stated to use nothing less than 91, but several people have told me their bikes run "just fine" on 89 and even 87 octane fuel.

My understanding is that bike engines - especially air cooled ones like on my Harley - run hotter and have higher compression ratios than car motors; if too low an octane fuel is used there will be pinging (pre-ignition, detonation, whatever you want to call it) which eventually can cause serious problems like burning holes in the tops of pistons. Car engines are built to run on 87 octane (or at least my POS '97 Chev Cavalier is, according to the owner's manual) because they have lower compression ratios and better heat dissipation and can handle fuel that burns quicker without causing pre-ignition.

I've tried 87 and 89 octane in my Harley (and in my previous rides) and found that it caused pinging, especially in hot weather and under hard acceleration, so I've contined to use 91. I've talked to many dealers and mechanics over the years and very few, if any, have ever recommended using lower grade fuels in bikes. But it seems there are a lot of people on bike forums who dispute this and claim that any bike can handle low octane fuel. I've researched the topic online and have found many FAQ sites that deal with fuel requirements for car engines but nothing about bikes.

So... my question is, does anyone have irrefutable proof that running a bike on low octane fuel will or will not cause any long term damage?

No proof, but my dad's 2002 BMW R1150RS calls for premium fuel with a RON of 95, but it does run just fine on 91 (highest available in Canada)

My new bike (2005 KLR650) calls for a minimum octane of 87, so that's what it gets.

Higher compression engines require higher octane fuel.

Everyone has heard the same stories as you for the most part (or so I imagine). I use a lower than recomended octane in my bike - sometimes. About half the time I use premium or mid-grade fuel and the other half I use the lowest grade. I have yet to hear pre-ignition problems with my bike - but I'm guessing this is on a case by case basis. I also like the idea of engine (and carb in my case) cleaning qualities of the premium gas.

If what you say is true of air cooled bikes, I wonder if you could just use premium during the hottest part of the year. I think they only way you will know for sure is to experment. One time with a bit of pre-ignition will not kill your bike - you just don't want it to always run like that - or the piston damage you mention will occur.

WhyteGryphon wrote:My new bike (2005 KLR650)

Y'know, I 've always secretly wanted one of those. We have a lot of dirt roads and firebreaks in the area I live and I need something to go bashing about in the bushes with every once in awhile. A think a Killer would be just the ticket for this!

No proof of damage, but I never really knew how much difference in mileage it made until I took the challenge. When on a bike trip with a friend on his Triumph, he would always burn premium while I opted for the cheap stuff (as my bike runs just fine on it). Every fill, (and there were LOTS of them on this trip), I would require about 20% more fuel than him. He insisted that it gave him better mileage so when I switched for a day, I consistently used less than 5% more than him. With a range limited bike like the VTR, this made a huge difference. Now that premium is only 10% more in cost at the pumps, it is actually cheaper to run as well.
Before I made the change however, I always ran the cheap stuff and never damaged and engine for doing it to answer the question.....sort of.

I switched from premium to plus on my last fillup and it runs lousy now. I'm hesitant to yet declare that the fuel is the only reason but it easily could be.

mysta2 wrote:I switched from premium to plus

Just out of curiosity, what is the octane rating of "plus" down there?

i run nothing but 92...my buddy just got a monster though and it says to run 95 or better...we cant find a pump that has anything higher than 93.

I run premium, The cost is higher but at 50 miles to a gallon who cares.

Aggroton wrote:i run nothing but 92...my buddy just got a monster though and it says to run 95 or better...we cant find a pump that has anything higher than 93.

From here -

http://www.sunocoinc.com/market/gasolinef.htm

I found -

GASOLINE
Sunoco sells four grades of gasoline – five in the MidAmerica market – compared to the "standard" offering of three grades. In addition to Regular (87 octane), Plus (89 octane) and Super (93 octane), Sunoco markets Ultra® 94 – the highest octane available at any consumer pump – throughout its 21-state marketing territory. An 86-octane Economy grade is also available in Ohio, Michigan, Indiana, West Virginia and Kentucky.

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Note above that they state "Sunoco markets Ultra® 94 – the highest octane available at any consumer pump"

So looks like you could go as high as 94 if you have a Sunoco in your area.

I remember when I was in my 20s we use to drive 70s muscle cars, usually in a well weathered state. This was the late 80s. We use to go to the Citgo near us (in the front of a 7-11) an they had high octane racing fuel. Our cars were pre-74 so they ran best on leaded fuel. We use to pay the premium to run that in our old cars.

Then again we use to like to pretend these worn old rust buckets were hot rods. 71 Pontiac Firebird - blue with rust all over. 350 2 brl Rochester. It had its frontend clip held on with coathangers (twisted to hold like craft wire). We were nuts.