Oh my! This impossible-to-settle argument again?
I'll cut-and-paste something I wrote one of the other 25 times this has been "discussed."
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I've owned 46 vehicles in my life from simple, old-school hot rods to modern performance cars to 18 wheelers, and just about everything else. I do all my own work, never taken one to a shop except for a few free things like warranty work, and a hand-full of alignments. I'll follow the manual if I think I should, not because someone on the internet recommends that I do what they do. Since about 2003 I've been running my Supra on the stock short block (ported head, aftermarket camshafts, fuel system, and other modifications) in a state of tune that makes more than 850 HP from 3 liters. For THAT engine, I run at least 110 Motor octane, and often higher. No premium in the LX or GX, though.
Here's something further on the subject of why manufacturers recommend higher octane (but I won't go into detail, it being Christmas night, me having things I want to do instead....)
A modern engine of good design, in good condition, that's been burning good quality fuel, actually requires several octane points LOWER than the manufacturer states in the "manual." The REASON for this "discrepancy" between what the manual says and what the engine actually needs is that manufacturers specify the octane requirement for a new vehicle based upon what the condition of the combustion chambers might be
after the vehicle accumulates several tens of thousands of miles with less-than-ideal quality fuel. Or what it might need after the engine is older and perhaps has started burning some oil (which will very likely lead to deposits)
The primary determiner of octane demand ends up being the temperature that the air/fuel charge reaches
before it is ignited by the spark (I won't go into why, but it is). In a clean engine ( that is, "clean" combustion chambers), the temperature that the air/fuel mixture reaches will be relatively low because a lot of the residual heat from the previous combustion event is dissipated through the valves, piston top, and the rest of the cylinder head surface inside the combustion chamber. In this clean engine, when the new charge of air/fuel mixture comes into the cylinder, it doesn't soak up too much heat from the combustion chamber surfaces because they've "cooled" down a good bit. HOWEVER, in engines that burn oil, or that have burned a lot of fuel that is prone to leave carbon deposits, there will be an insulating layer of deposits on these heat-sink surfaces. This layer retains much more heat than does bare metal. Consequently, the fresh air/fuel mixture gets heated several degrees more than it would in an engine with little or no deposits inside the combustion chamber. The result is that the fuel needs a significantly higher anti-knock index, a.k.a., higher octane in these old/deposit-laden engines.
Manufacturers cannot afford to develop a reputation of their engines pinging/knocking/crapping out when they reach 100K miles (or whatever) simply because they've been burning poor quality fuel or for some other reason have developed some deposits inside the combustion chambers. If they did, the resale value of their vehicles would be in the toilet. Therefore, they rate the octane "requirement" high enough that even an older engine in not-so-great condition will be okay with it.
The then-R&D manager for the company that developed Techron back in the day is an acquaintance of mine. He is mostly retired now, but is one of the worlds foremost authorities on fuel additives, including octane boosters. He gave me my my understanding of the OEM octane "requirements" thing. Now you know (unless you choose not to believe.)
Quote:
"If you ever towed with your truck you'll understand about this more readily. I used to tow 7500 lbs. fifth wheel driving at sea level up to high altitudes in the Rockies. I live in Foothills region. Experience is a good teacher...."
I've towed plenty - 5th-wheel trailers with earth-moving equipment (very heavy) and livestock trailers (only about 13K pounds). I've built engines specifically for some of those pulling trucks. But that's irrelevant here because the subject is whether or not premium fuel is needed for a 200 series LX 570, most likely going to the grocery store at a maximum of 40% throttle opening. They don't, IME.
If ever other time I get gas which is about every 100 miles I use regular then next time I use premium the octane level would average out to 90 which should be close enough and save me 1/2 the difference in cost 
In my world, that's a 90 cent difference.
I surprised myself the other morning by being able to compare the outside diameters of a 285-70-17 to a 285-65-18, in inches, in the shower. Still got it. 
However, my memory evidently aint what it used to be because I've already forgotten which I determined was bigger! 
