I have come from flatland Florida to the hilly area of northern Alabama, southern Tennessee for a vacation, and I have quickly learned that my curise control (CC) hurts my gas mileage on these roads. I would prefer my Prius to use the down slopes to gain MPH and use that momentum for the up slopes. The CC does not allow for this, and uses the downslopes for "breaking" in my opinion, giving me 99 MPG, but I have no momentum for the climbs. Anyone else NOT use CC for hilly/mountain driving, or is it just me? Brad PS. I driving on average 50 MPH in this area.
Our hills are bigger in Central New York than in Tennessee or Alabama, and I find that using cruise control in up-down terrain improves MPG vs using my foot. I believe CC intuitively does a better job at sensing when to brake downhill and when to accelerate uphill than I do. I've tried it both ways, and now drive with CC on long up-down trips. What kind of improvement? Between 1 and 2 MPG. Average: 46-48. Best MPG after 8,000: 52.2 on a 500 mile round trip to New York City and back, mainly thruway at 65 mph but also in city crawl.
Here is a reply from mountain country. I never use cruise control. Two years ago on a 4000 mile trip I diligently used CC for about 1000 miles through flatland, hills and mountains. For each my mpg was higher by not using CC thus I stopped using CC.
The CC in the Prius does not do any braking. The most it can do is back you off to zero throttle. There's no question that someone carefully using the accelerator by foot can markedly out perform the CC...I repeat, no question about it. CC allows speed to drop about 2mph from the preset then very aggressively powers the car to get back up to speed. On a moderate hill even this can mean a WOT (Wide Open Throttle) condition that is very fuel inefficient. Under full control of the driver one can feather the pedal on downhills to allow momentum to gain at the cost of gravity, acceleration can begin BEFORE one gets to a hill and one can often maintain the ICE rpm under 2300 rpm or at least <3000 rpm, avoid the WOT condition and keep the climb and aggressiveness under complete control. Done wrong one could under perform the CC...no doubt about that either. But there is no question that under the practiced foot of an experience driver, particularly one with Scan Guage or CAN-View to help monitor the ICE rpm that driving without CC can improve FE by at least 10-20%...conservatively.
