With the cost of fuel being what it is right now (it is expensive by US standards at least) you can be pretty sure that BMW and others would make the most of the ability to run their cars on regular grade gasoline if was truly non-detrimental to the car's overall well-being. The bottom line is that BMW really doesn't have a dog in the fight, it's not like BMW or any other manufacturer is gaining any additional income or revenue by recomending premium. The car is designed to run on premium It has to adjust its timing to run with lower octane gasoline, and in doing so some performance potential is lost. Conversely, there is no benefit in going *above* the BMW recommendation. You can fill your tank with 100 but you won't notice any increase in performance. All people are saying is that there's no incentive for BMW to specify premium over regular if it were indeed true that regular works just fine. The reality is that the car can accommodate it, but that it not the same as it working optimally.

 

I believe BMW recommends premium because it is required to make their claims about peak performance true. Also, requiring premium goes hand in hand with their image as a premium brand. These are two very good incentives to recommend premium over regular, even though BMW admits running 87 will cause no damage. (Note: this does not apply to turbo cars which actually require premium)

Some more reading:
http://www.consumerenergycenter.org/...s_premium.html

http://www.scientificamerican.com/ar...tion-premium-g

 

The first article actually says what we already established - there is no benefit in using a higher octane rating that the manufacturer recommends, and using a lower rating can impact performance.

I'm struggling to see any actual evidence in the second article to support the author's contention.

In the meantime, here is an article from Car & Driver that is perhaps much more on point.

The money quote:

"Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price. Cheapskates burning regular in cars designed to run on premium fuel can expect to trim performance by about the same percent they save at the pump"

http://www.caranddriver.com/features...emium_-feature

 

That test uses the E46 M3, which has a compression ratio of 11.5:1, (the E60 M5 is 12.0:1, and the E60 530i is 10.2:1 by comparison). One would expect to see more dramatic losses in power from the M3 than from the OP's 530i. Also, we can all agree that there may be power loss from lower octane fuel, but since mpg is not tested in this article, it goes nowhere to further your point that the amount you save at the pump is outweighed by decreases in fuel economy.

Interestingly, even though the compression ratio is so high, "neither the BMW nor the Saab suffered any drivability problems while burning regular unleaded fuel." This statement bolsters my original claim that unless you are trying to wring out the last few percent of performance from your engine, using 87 will have no effect.

 

At the end of the day, it's your car and what you put in it is up to you. I still maintain that ignoring BMW's recommendation by putting regular gas in a car designed for premium is lunacy. It only has no noticeable effect because the car tries to compensate for the lower octane. Either way, it is possible and quite probable that is indeed having an actual effect, and that this effect manifests itself in the performance and MPG hit that you suffer. Every source quoted so far acknowledges or tacitly acknowledges that the these are the consequences of using lower octane fuel than BMW recommend. The question is why would you want to take these hits when they are entirely preventable? It really makes very little sense...

You ultimately save very little, and you don't get the best out of your car - and these performance issues are, of course, acknowledged by BMW. These are not risks that have been pulled out of thin air. Simply put, we're literally talking $2 to $3 per tank difference in cost. That's not an appreciable saving. Your point seems to be that it doesn't matter because you can live with reduced performance. My point is that the cost difference isn't worth the risk and the trade off. Take these two together and you get to the heart of the matter, as I posted earlier A driver who is not interested in the former (performance) and worries about the latter (an additional cost of around $3 per tank) probably ought not to be in a BMW.

 

This guy can't ask a simple question without some people making him feel like he's a poor man driving a rich mans car.

 

It's about wise spending. Nothing to do with rich or poor.

 

In most places I've been in the US the price difference between regular and premium is 20 cents so that's only $3.60 savings at most per fill. Now I have seen some places with a lower luxury car population, like my hometown Birmingham, Al, where the difference was sometimes 40 cents or more which being at least $7.20 more seems a little more understanding. My belief goes with the majority who say if that little bit of money makes a difference overall maybe you shouldn't have the car to begin with, considering the expensive repair costs that goes with these cars.

 

Its not wise to put 87 or 89 in your BMW...

 

That's fine to have an opinion like or unlike yours. To his each own...