My car is designed for 98 octane (RON) fuel:
However, it lives in a country where the only choices at the pump are green nozzle or black nozzle, and the green one’s 95 (the black is diesel, in case you’re wondering).
I spent ten days in France recently so I took the opportunity of treating it to 98, at a cost: it’s about 10c a litre dearer. No, I didn’t buy at this exorbitant autoroute price. Gasoil is diesel, for reasons unclear.
I came home with a few litres left and so I was able to experiment with 98 on familiar roads. The outcome? There’s noticeably more go on the dear stuff, with the turbo doing its boosty thing to more effect.
So there we have it. Using 95 in a vehicle designed for 98 does make a difference.