[gimlithepirate]

Been doing some roadtrips through West Texas in our hybrid escape, which is murder on my gas mileage. The combo of flat drives, lots of wind, lots of AC, and very high speed limits (up to 80 MPH in sections) means I rarely get better than 30 MPG.

What I'm wondering is whether people have seen significant gas mileage savings by limiting their speed to 75 mph. On past vehicles, I've done the math and for a 600 mile drive the gas savings simply wasn't worth it. However, if we're now talking 20-25%, that's a different issue.

Any thoughts?

 

[jpohlman]

Best fuel economy on a a Hybrid is usually 55-65 mph.
The ONLY time I've ever seen a car get better at higher speed was our 2014 Escape Ti running premium, it got 36mpg at 90mph but only 27mpg at 75mph.

 

[BreckB]

One difference for us, as we have a PHEV, so I had to do a little math to figure out the gasoline MPG. We recently took our first trip with the intent of burning out the ethanol gas. Drove the "range" down to 1 mile remaining. Then filled with 11.2 gallons of pure gas in a tank rated for 11.1 gallons. Taking the total miles driven (over 1700) and deducting the EV miles, we had our "gasoline miles" / 11.2 = 29.8 miles. Next goal for a trip is to calculate the MPG in hybrid mode. We just don't hit the road very often. (This was our first tank since we bought it Feb 1, which is why the ethanol gas had to go. ) Keep in mind that the aerodynamic drag goes up by the square of the velocity, so 75-80 MPH is really affecting your mileage. Every car has a optimum speed for a gasoline engine where the "Brake Specific Fuel Consumption" is minimal. On some days when you don't have wind, and can make a long run, use your cruise control and don't change your speed. See what happens at 75 / 70 / 65 / 60 MPH for 150 miles or so. Use the same initial gas station to fill the tank before you leave on your trip, and likewise, use the same station at your destination at the end of your run. You should be able to establish the "right" speed for fuel economy. IE... we know our RV is most fuel efficient around 62 MPH - up to around 50 MPH, the main drag is resistance to rolling (tires) but then aerodynamic drag begins to really take over.

Post what you learn... I just don't have the opportunity to make these runs to test mine.

 

[User3657]

My thoughts, it's a waste....you don't get a hybrid and consider going 75. You do the speed limit or slightly below and take side streets 😁don't know what your life MPG is but I bet you could double it.

 

[Thenorm]

aero drag is proportional to v^2. here is a simple chart of speed vs speed^2 normalized to 65mph.

aero drag is the predominant drag over 50mph. there will always be some baseline rolling resistance, and friction in the engine, etc..

90mph is twice the aero drag of 65mph.

50mph is almost half the aero drag of 65mph

75 to 65mph saves you ~40% of the aero drag portion of the total drag. maybe that is worth 10% improvement in fuel economy?

 

[fbov]

aero drag is proportional to v^2.

True, but there's more! This is drag force, so it links to TORQUE requirements.

For POWER, you multiply the force by the velocity, resulting in a v^3 relationship. Even worse...