Real World Highway MPG @ 75-85 MPH speeds?

The speed you choose to drive at is going to make much more of a difference to the "gas pedal burden" than any tweaking you can do once you reach that speed.

 

See fuley results below. Ive only been entering data for 3 years.

 

Toyota Prius C MPG - Actual MPG from 1,111 Toyota Prius C owners

 

I never played the tire pressure game because that is less about mileage in my opinion and more about safety. Tire pressure is a correlation in the grip on the road and the ability to turn in precise measure without losing traction. The lower the pressure the wider the footprint. Too low of course creates drag and blowouts. Too high increases risk of hydroplaning in wet conditions or sliding in high demand turns. What people see as their mileage advantage is how much less grip the tire has on the pavement. Less traction forms a higher mileage figure. That is the great thing about LRR, Low Roll Resistance tires that come on the car. There is a balance between the traction pressure and the load. These tires will keep spinning without constant coaxing by the drive shaft through the axle. Hence it is possible to ease off of the gas pedal and coast on these tires without using either battery or gas.

 

I never counted my fuel-ups. But in 33k miles I averaged 54mpg.

 

45mpg on a grade @80 is exceptional for uphill. This car loves going fast. It also loves to forget to burn fuel. So give it every chance to work mechanically. For me at any speed 45mpg was too low. I always demanded more conservation on my car. It isn't the push to focus on because that consumes fuel. It is knowing when to stop pushing.

 

Assuming flat terrain and if I believe my ultragauge output, I get 46mpg @80mph. As low as 36/39mpg going uphill, and obscenities of 249mpg downhill. I get that there are more precise ways of measuring, but it's outside of my effort level.

 

It is not something I measured in a similar way as you. I noticed trends at certain times and focused on a goal of raising the average for the trip as a whole.

 

If you're driving at higher speeds, tire pressure increases are recommended in most owners manuals. Knowing that higher tire pressures are recommended, it goes without saying that it's safe to use higher pressures and the lower pressure specified on the door are only minimum tire pressures. I've found most car's handling is significantly improved and risk of hydroplaning is typically reduced with higher tire pressures due to a potentially narrower tread pattern. 40PSI really is the best PSI for the Prius as higher than that can sometimes be considered excessively harsh with questionable benefits. On really slick snow covered roads, playing around with the tire pressures (either really high or low) can mean the difference between being stuck in the snow and plowing through it.