He is referring to a very special case where high speed aerodynamic drag on the downhill exceeds the battery cycle losses. Even driving the mountain highways out west, I've never found an example of where this would work, but if you could find a long, very steep road it might happen. If you are driving in ups and downs, for good efficiency you would let your speed trail off on the uphill, meaning you start down with very little speed. By the time your speed gets up to the high drag region, you should be starting up the next hill, and therefor slowing down. Tom
I use CC to help me avoid speeding and the radar CC does minimize stress and adds a margin of safety on long and monotonous drives. My biggest complaint about the Prius and other CCs, including the radar CC in the V with ATP, is the aggressive acceleration when the set speed is resumed. Watching the instantaneous MPG on the Scangauge II suggests that a carefully controlled resumption of speed, using my foot, is more economical than the more abrupt acceleration of the CC. A more minor limitation of CC is the absence of the more efficient P&G, although, other than experimenting, I seldom use the CC at P&G speeds.
I used CC in my previous car to break my speeding habit. Now I can get much higher mpg without it. It's a great way to maintain constant speed but holding a constant speed doesn't net the best mpg, even on flat roads, in hybrid or non-hybrid cars, as long as an ICE is involved. CC may be good for EV's, though.
read this: http://priuschat.com/forums/gen-ii-prius-technical-discussion/67241-high-speed-prius-notes.html On Gen III the drop happens at slightly higher speed. Can't find the source but there is a speculation that at ~75MPH there is some issue with aerodynamics. there are 2 factors at play: - seesawing speed up and down increases overall aerodynamic drag losses over the same course. At lower speeds this is more then offset by optimized powertrain usage, but not at higher speeds. - ECU is programmed to minimize battery use at high speeds. Using CC forces to use it on uphills.
I have over 50,000 miles on my 2010 Prius V, 17" tires and more. I have made 3 major interstate trips, 3,000 miles, 3,500 miles and 4,000 miles. I have driven through the mountains of Utah, Wyoming, California, Arizona, and much more. I run cruise a lot. I use it in town on my work commute and I use it on long highway trips. It handles mountains just as easy as flat land. The only time I shut the cruise off when I might otherwise normally use it is when going down LONG and steep hills ... and then I use "B" ... which is the Jake brake on the Prius. An example of this was when we went down a stretch of Interstate 8 west of Yuma where we hit a 6% downgrade for 13 miles. I log all my vehicle data in a spreadsheet ... gas, service, car washes, whatever. I have learned that cruise gives me whatever mileage I am going to get much easier than not using it and getting leg cramps instead. I have also learned that I can get better mileage with cruise than without. Many roads which LOOK level ... aren't. Your cruise control will notice and save you gas. I have tried the pulse and glide tricks and whatever else I have read about. In the real world, driving about 2,400 miles a month, there just is not enough difference in mileage between cruise and manual driving to make the tricks worthwhile. Forget the gimmicks and ENJOY your car!
This is the kind of driving habit that drives those with cruise control nuts, slowing down, speeding up. With the hilly terrain I encounter, the cruise does it well for me. The cruise on the Prius is much smoother others I've used. On the highway, I've found a constant speed give me the best general MPG, and helps prevent speeding, and doesn't cause a parade of cars behind me on the hills.
I drive 90+ miles per day commuting. I use CC and Eco mode, am averaging about 49.5 MPG in my 2011. CC seems to help out, plus its nice to not press the peddle.
