Ok, folks. This theory is untested, but I have some counter-intuitive suspicions. This post is an adjunct to my prior post on using cruise control for improved mileage.

It *seems* that my TCH gets better gas mileage at 65 MPH rather than at 60 MPH, and that my MORE CONSERVATIVE freeway driving appears to net worse MPG results.

My theory is that a 3,600 pound TCH traveling on the hilly freeways of San Diego MAY be better able to sustain greater ROLLING MOMENTUM at higher speeds (to conquer the next hill) than the mileage I can achieve by efforting over each hill at lower speeds. I believe that rolling momentum would be more significant for heavier cars, and therefore more crucial for a TCH than for a Prius.

Any facts/data to support my speed vs. rolling momentum theory and their effect on gas mileage?

 

I have found the car often gets the same mileage at 60 mph that it gets at 80 mph but that really depends on various factors. Of course accelerating to 80 mph costs more gas, so it does use more gas over short trips, but over long ones it seems fine.

The common tactic of allowing the car to slow down on uphills is of course extremely effective. Getting to a hill at 80 mph, and allowing the car to slow to 70 mph as it gets up it, saves alot of gas.

Certainly in terms of acceleration, the car gets far worse mileage at 10 mph than it gets at 40 mph, regardless of rate of acceleration. At high speeds, acceleration is typically at 20-30 mpg, but at low speeds it's between 2-10 mpg often.

 

Those are good techniques and points. I think I'll have to do my 18-mile course loop twice, once at 60 MPH and once at 65 MPH to see if higher MPH on these hills might actually produce a benefit that could be verified.

 

I think another factor has to do with the fact that the Camry has a larger, more powerful engine -- this will cause its peak efficiency spot to be a higher speed than the smaller 1.3 and 1.5 engines on other hybrids, which peak at around 50mph. While that may be lower than 65mph, if that is average 65mph driving with load and not steady 65mph, you may be dropping below the efficient range on some of the hill climbs.

 

I've been topping out the Eco gauge when toodling around 40mph and the ICE shuts off. I actually made it through about 4 miles through town, stoplights and all, with the ICE off entirely, which surprised me how far I could go given the rapid drain rate of the batteries. Outside of this 40mph sweet spot, the milage seems to vary more on occupant load rather than speed of the car. While that is to be expected, it surprises me the extent of the difference. Not once have I been able to get the TCH to accelerate from a stop without aid of the ICE when all my family of 4 is in the car. Brief acceleration (spinning tires, white knuckles, reble yell and icy stare from wife) doesn't seem to diminsh the effeciency as much as expected. Since I'm still in the break-in period, I won't do that again.

Please keep in mind I've had this thing for a week, so I don't yet have imperical data to support milage information and am basing all my info by use of the gauges.