Highway @ 75mph

That would be a good start and see how your mileage is affected.

 

Just my way to drive, Eco On when AC On, Eco Off when AC off. No cruise control. Use Eco Score screen and trying to keep the green bar at around 12 o'clock if I can even downhill or uphill. Of course it'll be faster downhill and slower uphill but if no one behind me I try to keep it that way.

 

Cruise vs no cruise: the flatter your terrain* the better cruise does, as you get ups and downs, cruise does not look far enough ahead.

When in cruise, the modes (eco, normal, power) have no effect since they alter how the pedal reacts to your foot.

* I can drive 150 miles and only gain 90 feet of elevation, so I fall on the flat side.

 

Sounds like your getting about all you can get at 75 mph. Increasing tire pressure dosen't really get you enough MPG to make it worth it. It just makes ride harsh and rougher. I have run my tires at 42psi and at 35psi with no diff in MPG. I normally run 75 to 85 on the interstate and get about 45 MPG. Beats the hell out of the 24 MPG i got with my Honda. Don't get hung up on MPG and just enjoy your new ride.

 

Don't assume, do check and control them. Mine arrived with 39-40 psi, and this was a surprisingly common dealer prep 'failure'.

While I know this isn't the reply you want, do look at this chart for the regular Gen3 liftback. It basically shows what is possible at fixed speeds, you can gauge how much or little you are missing out. I can't point to a similar 'c'-specific chart:
Updated MPG vs MPH chart | PriusChat

 

Honest question: what's wrong with that? I think that's pretty decent as I got about that in my gen3 @ 70mph and about 41-42 in my gen2.

 

Running constantly at that speed, it's mostly aerodynamics. Lowering your car would help, covering your grills would also help.

You can also go to ecomodders and learn how to replace your wheel covers with smaller air openings, tape panel gaps for better aero, or go all the way and add wheel skirts, and a boat tail .

 

The highest numbers you will get will be when you are in stop and go traffic. Cruising on the highway you will be using the gas motor mostly. I've hit the low sixties when in traffic because I'm barely using the gas while creeping along

 

These are the tweaks I can think of:

1. Higher tire pressures
2. On next tire replacement, get the lowest rolling resistance tires possible (e.g. Michelin Energy Saver A/S)
3. Purchase a scanguage and use it to hold the engine rpm more in the 1400-2200 sweet spot by allowing deceleration on hills. See this for reference, which is likely very similar for Prius C. In hypermiling terms, this is called "driving with load".
4. Ensure S4 Mode is engaged prior to getting on highway (scroll down on page to see Prius modes).
5. Aero/eco mods - grill block, moon caps, etc. See especially the aero mods on this page.

I personally vote for getting a full boat tail, like this guy. Okay, you are probably just looking for simple tweaks, but it never hurts to know what's possible.

 

Well, the op never said what the air pressure was or is, but at 75' only a Tessla or equivalent will get better mpg's, keep the cabin filter clean, keep the ice filter clean.

If you insist on better mpgs draft other vehicles, it's "kinda" a choice, Darwin doesn't draft at 75.

 

The car is only two weeks old, so it is still breaking in, I find that between 66 and 70 MPH is the sweet spot for this car. I don't know how flat your drive is, but at these speeds I see an average of 55 MPG with A/C on. As someone else suggested, buy a Scanguage and set one of the readings for RPM, Keep your RPM below 3,000 and this will help.

 

I n a highway the machine at that speed needs to use the gas engine and that is the one that would domain, so have a economy better than a yaris or a corolla depends of the type of tires, transmission CCV, aerodynamics of the car and pressure of the tires. So the last is the one you can control if you are using the required tires. Also you may need to maintain the speed constant and avoid the increase in gas in the uphills. So 40 psi I believe is a good number because a over pressure tire is a problem. As harder the tire more able to loose control at high speed, because the transaction in between harder surfaces is less. Also can break it more easy if you hit something hard or hit a hole.When the tire is so full can not expand and dissipate a bump or what ever appears at the road. Also keep in mind that the friction coefficient of the tire decrease as it got harder! That means less traction specially at high speeds. So I think over 50mph close the windows, turn AC on in eco mode, mantling the speed and have the correct tires at a correct pressure, that is the best I can do for the machine. Remember to check the air filter most be clean as possible, and the oil is very thin to increase economy and should be clean as possible to avoid friction.

 

You would most benefit by using the Ecoscore screen through all parts of your drive. As a visual cue it teaches you how to drive your car at any speed for the most mileage. The sliding vertical/curved bar is the best friend you would have. Nevermind that some people call it a tach. It could function like a tach but is significantly more sensitive to changes in the operation of the ICE. The closer you manage to keep the solid line on the left the more mileage you will have.

This applies to any speed. The less you ask gas to feed the movement of the car the longer it will go without needing that gas.

Coasting by releasing the accelerator after your desired speed has been reached is the first thing and maintaining desired speed with minimal pressure on the pedal guided by the Ecoscore bar will provide you with driving happiness.

 

My wife commute is around 60-65 miles a day. Most of her daily trip is on the interstate, but she does have to cross a mountain. When she drives, we usually see 45-48MPG. When I drive the same trip, we 47-55. Both of us generally drive at 70-75mph, but I take off much slower, and tend to coast more when stopping. On days I am not in a rush, I drop my speeds back to 55-65 and I often hit 58-62 mpg.

I also found out that that driving the car a little less aggressively when its cold REALLY helps out. I assume this is due to the gas engine is running to getup to normal temps. In the winter months, I will usually take the back streets for a few minutes before I get out on the highway. This seems to really help over all mileage.

Again the numbers you are posting are not bad. I would be perfectly happy with those. If your looking for more. Consider airing up your tires, drive less aggressively until car gets up to normal temps, be gentle on the accelerator when passing or taking off. Due to our roads having a fair amount of vertical changes, I tend to run in ECO mode and leave the cruise control off.

 

Also beneficial for the engine.

 

Dropping speed to 70 mph could increase mpg maybe 1 or 2. I haven't cruised over 65 mph and at that my C was achieving around 51 mpg flat with some hills. Best of luck!

 

I posted this a while back, check your tire pressure, and reducing speed would be your two most significant changes to increase your MPG if time is not an issue.

Having done multiple trips(10+) between Houston to Dallas, (~250 +/- 15 miles), Speed is the biggest factor. I have driven at 65 all the way, added about 30 minutes to the drive (total drive time 3 hours 55 minutes), and attained 42 MPG(Calculated manually at the pump). (A/C on the entire time in the texas heat, temp: 95+) Driving same day back at 75 MPH+, MPG dropped down to 37 MPG, saved me time(Drive time 3 Hours 22 Minutes), which was more valuable to me than the fuel savings. Driving slower I had 4 bars of gas on the gauge when I got there, I had 2 bars lefts when speeding. Lets do the math:

Trip 1(65MPH): 250 miles / 42MPG = 5.9523 Gallons used. Drive time 250 Miles / 65 MPH ~3 Hours 55 Minutes
Trip2(75MPH+): 250 miles/ 37MPG = 6.7567 Gallons used. Drive time 250 Miles / 75 MPH ~3 Hours 22 Minutes

Difference in Fuel used 6.7567 - 5.9523 = 0.8044 More Gallons Used
Cost: 0.8044 x $2(National average 1/7/2016)= Spent $1.6088 More.(Values will be different depending on your local gas prices, Gas during last summer was higher, national averagewas $2.780 Actual cost was higher for me)
Time Saved: ~30 minutes
I believe saving that time is worth more than $1.6088 for me.