The difference between the two measurements is caused by the engine’s operating conditions, and the Research ® octane number is usually nine to eleven numbers higher than the Motor (M) octane number.
Our manuals state that we need a RON of at least 95 - Is it safe to say that with that 9 to 11 point spread, that the (R+M)/2 number that's marked on the pump is within half of that spread - 4.5 and 5.5 below that gasoline's RON, or is it remotely possible that a gasoline might have a smaller difference between its R and M?
If Shell's 9-to-11 point guideline is solid, then a pump marked 91 should have an R of 95.5 to 96.5, no? Has any TT'er heard something different? I can just see myself thinking I'm so smart buying something marked 92, and it actually being some unexpected case of zero R-N difference like (92R+92M)/2 = 92 on the pump and 92 RON!