Using 87 or 89 octane fuel ?

I have a 2011 328i and although BMW recommends using 91 octane fuel, I was considering trying 87 or 89 octane fuel. I was wondering if anyone has tried running lower octane fuels? If so, did you notice any knocking/pinging, decrease in performance or reduction in gas mileage as a result?

I have been using in my 03 325i 89 octane with no issues on performance, yes there is a slight mpg decrease but I'm still saving more then paying for 91. Since yours in naturally aspirated engine I would see no issue with running 89 octane. BMW on some models does have a programming conversion to allow for lower octane fuels to be used in there vehicles.

Don't be a cheap skate, treat your machine to gormet octane.

In all seriousness, I live on a very short financial shoe string and one thing that but absolutely cannot cut corners on is what I put in the tank if my machine. Inferior fuels have been noted to add deposits and reduce the life of the fuel system. I would say if you're only looking to keep this car for a three year stint, go for it, but if you're looking to have a life long companion, feed it the good stuff.

I should clarify that I'm asking about putting 87 or 89 octane gas from Mobil/Shell/BP etc, not gas from a "second rate" station. So far what I have been doing is putting in half 93 octane and half 89 octane in order to get 91 octane since they don't sell straight 91 octane in my area (except for Sunoco).

I have experienced fuel system problems with inferior gas with a previous vehicle which is why I switched to Mobil/Shell/BP etc. What I'm currently seeking is maximum efficiency per dollar.

Thanks for the replies so far !

Thanks for the clarification! I have often wondered what would happen if you were to mix the higher and lower octane, then I just kind of figured that I could save the hassle by just getting the mid grade. Perhaps my logic is skewed.

Good call in the higher standards of gas stations, I have always put my faith in the ones with the least spastic nozzles and until recently just threw fifteen dollars at a time in, from various gas stations, to assure that I have all sorts of gas in my Tank.

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What is needed is a clearer understanding exactly why BMW recommends a specific octane, and whether the fuel control systems have any tuning or accommodation for lower octane fuel without creating running problems. Given that BMW has to cover a large variety of possibilities over which it has no control, one being that anyone might not pay the least amount of attention to BMW's specific fuel recommendation for a higher octane gas, it seems likely that BMW has their fuel programming designed for the engine to run safely on regular gas, but possibly not optimally for BMW's desired performance, or the engine's potential. Running lean can be disastrous for an engine, I doubt BMW would risk their engines and reputation counting on anyone and everyone filling their cars to always be filling with the recommended gas, or even expecting all gas to actually be the octane it's rated. It would be interesting to hear what BMW has to say about it. I would think there also would be some comment about it in the owner's manual.

Mine gets nothing but BP (was Amoco) Ultimate 93 octane.

There is a section in the owners manual but it's not very clear:
"Super Premium Gasoline/AKI91 This gasoline is highly recommended. However, you may also use gasoline with less AKI. The minimum AKI Rating is: 323i,328i/xDrive: 87 335i/xDrive: 89. If you use gasoline with this minimum AKI Rating, the engine may produce knocking sounds when starting at high outside temperatures. This has not effect on the engine life. Do not use any gasoline below the specified minimum grade. Otherwise, the engine could be damaged."
I wish they would have added a sentence or two to explain what the lower octane would do to fuel economy or performance. I might try an experiment with 91 vs 89 and see what it does to fuel economy.

I am sorry, but it is beyond me why you spend money on a car then pinch pennies at the pump.

Bassackwards.

Thank you for your constructive input. Have a nice day.

I think it's reasonably clear; they're telling you what's recommended, the minimum that's safe to use, and warning about using less than the minimum recommendation. What it doesn't address is translating those octane ratings into something meaningful for drivers in the U.S., where gasoline octane is an average of RON & AKI. So, the question becomes how do U.S. octane ratings compare to AKI. If you google that up, I suspect you should find plenty of detail addressing that issue. As for effects, yup, your best bet is likely just try the different grades and track what you find.

"comparative spreadsheet to figure out the monetary difference between using mid-range gas versus premium"

I HATE spreadsheets, especially when they're fresh out of the dryer and full of static cling...oh wait...

I admit with rising prices it's annoying to fill up. My wife's ride (non-BMW, sorry) takes 87 octane while I'm paying 40-cents more per gallon for BP 93. But I knew what I was getting into when I got this car (again). Not sure if I'd notice the knocking if I filled up with 87, but I've always put premium in my cars and it's just part of owning a BMW. I accept it.

Sigh. In my area, most gas stations are carrying 87, 89 and 93 octane fuels with the exception being Sunoco which does carry 91. In order to get to the BMW recommended 91 octane, what I have been doing is alternating my fill ups between 89 and 93 when I get to half a tank. Since I'm getting sick of stopping twice as often to fill up, I started thinking of just filling up when I get to empty with 89. However, before I did this, I figured that I'd ask people who've owned these cars longer than I have what their experiences were if they had run lower octane fuels. It was just a question.
That said, I'm still running half and half mix. I'm planning on trying a full tank of 93 and a full tank of 89 just to see if there is any difference in fuel mileage.

The octane is one thing, the other aspect to premium fuels is the detergent package, of which in premium gas there is more of and better - that may or may not be of importance, but long-term usage of premium gas in theory should help minimize the buildup of deposits/carbon/sludge on valves and engine internals. If there is no intention to keep the vehicle long enough to where something like that could become a running problem, then that likely isn't much of a motivating factor in opting for super-duper. It's not necessarily a bad idea to run an engine into its upper rpm ranges every so often when driving (not just revving the engine sitting still).