Use 65-70 mph if you want mileage while not being a road block. And yes, 40psi is about the sweet spot for most tires between MPG and harshness.I have a 2017 volt. It sound like I’ll be putting air in the tires and drop my speed to 73 and see what happens. 😃
75mph = low-mid 30's mpg
70mph = mid-high 30's mpg
65mph = 40-ish mpg
60mph = 45-ish mpg
If you wanted good MPG on gas, you shoulda got a standard hybrid.