Octane grade for towing

It will depend a lot on the engine. The higher the compression ratio, the more it will matter. If you have a fairly pedestrian N/A engine, it might not make any difference at all. If you have a fairly high compression engine, plus turbo or super charging, and you're towing a TT, it could make a huge difference. Then there's the whole world in between those two extremes.

The engine on our F-150 is high compression, and it is turbocharged. The owner's manual recommends premium when towing. So we do that. If you have an engine monitor, you can see the difference in the ignition advance.

I decided to try the higher octane for two reasons. Out west, the "regular" gas was 85 octane and not the 87 I expect and the minimum Nissan recommends for the Frontier. Midgrade there was 87 octane and premium was 89 or 91 octane (varied with stations). As much as we were already stressing the engine in the mountains, I did not want to add detonation to the mix. Some of the stations had ethanol free gasoline in premium. A couple had cheaper ethanol "midgrade" at 87 octane but the 85 octane regular and the premium were ethanol free.

Results seemed to indicate that the higher octane did not really yield a significant increase in mileage. Ethanol free gas did but I could not say the additional octane of the premium did much good.