>commuter cars can run on regular with no issue
>performance/luxury cars require premium
What's the point of the middle octane?
A lot of cars that 'require' premium would usually run fine on 89, thanks to the knock sensor.
Like, in Australia, my owners manual says my Toyota 86 SHOULD be given 98 Premium, but it can run 95 with no discernible change in engine performance. I put 91 in it once because I was on a back road, and the only service station within 300 kilometres only had 91, and even that didn't cause an issue - I didn't floor it, and the knock sensor adjusted accordingly.
What? 91 is our lowest unleaded, yeah. 98 is the highest that's available at most places, 100RON is available here and there, E10 is seemingly phasing out 91, and E85 is very slowly being rolled out at certain service stations.
my car would run fine on regular but the engine light comes on if I say the word "Ethanol" anywhere near it. Premium is my only choice
Blending regular and premium 50/50 in the dispenser is easy to do and lets the station make a little extra money. Oh, you mean what's the point for you? Well, I guess there were some older cars tuned to run on 89 octane leaded regular, they probably like the 89 unleaded better than 87. That's about it.
There's usually not a big enough difference between something like 95 and 98 to warrant a retune. If you're running a Flex Fuel sensor so you can run 98/E85, yeah you do, but it's generally a waste if you're just topping up with 91 here and there before 98 isn't available.