Fuel Octane

So I saw a news article today on Autoblog that said over half of all new cars today recommend premium fuel (as reported by energy.gov). So I checked my ‘23 Tundra manual, and found this.



It’s always been discussed that the Tundra only requires regular 87 fuel. But any idea what it means in the right column when it says “Research Octane Number 91”? Is the requirement 87 or is it 91?

 

"“Research Octane" is just one of two numbers used to determine "pump octane".

If you look at the gas pump, under the octane number it should say "Determined by the (R+M)/2 method". The "R" in the formula is the "Research Octane Number", the "M" is the "Motor Octane Number".

So if it says that to use 91 RON the MON would be at 83 hence (91 RON + 83 MON)/2 = 87 Pump Octane"

 

It says 87 right there, that is the minimum. 87 octane is the same as RON 91. Same gas, just different identification used in different countries.

 

I see that. But the manual doesn’t use “pump octane” or “motor octane”. It says “research octane number” in the left column with 87 in the right, and then again says “research octane number 91”.

I think your explanation is probably spot on and what they meant, but if so, they sure didn’t document it well in the manual by using “research octane number” twice in the table with two different numbers.

 

It says RON 87 and RON 91 in the same table. As it’s written, it’s ambiguous.

I used to write technical documentation and am nitpicking the shit out of it. I think automobile owners manuals are the most poorly written documents around. Doesn’t matter the manufacturer. I’ve owned nearly all of them, I read them when I buy a new car, and they all suck.

 

It doesn't say RON 87, it just says 87, which in the US is (RON+MON)/2, or typically -5 from RON.

 

Sure it does. Left column: Research Octane Number Right Column: 87
I know now what it meant. But it’s poorly written and ambiguous.