Tried an experiment. I've been messing with gas additives and when I completed that and pick one I continued, but this time the experiment moved to tire pressures. Wife’s car, 850 Volvo wagon, tires Yok Advid TRZ’s commutes 350+ miles week, sometimes over 450, all freeway speeds from stop and go to 80+ mph. Mileage with 40psi is 26.5 over about 4 tanks. Mileage at 36psi was 25.75 over three tanks. I would need more tanks but that looks like almost 3% and I don't want to go keep it at 36 because of the better mileage at 40. I curious what other might see if they try about the same spread in tire pressures.