we have finally taken our new prius out of town and into the 100 km / h zone. we have a question as to whether the cruise control reduces or increases your fuel efficiency? doesn't with an ICE it draws from the mileage? i noticed that the mileage seemed to get better when i wasn't actually pushing the accelerator. any ideas?
Depends. If it's flat as heck, I'm resting my leg! If there are rolling hills, I might be able to take advantage of them by coasting down and slowing chugging up. With the foot, I can cruise at a certain speed, take a look at the instant L/100km readout and slowly lift my foot til I just start to lose speed and watch the instant L/100km decrease. You'll be surprised by how much L/100km you can gain by lifting your foot but yet still maintaining speed. From that experiment, I figured CC is good enough.
You might try to drive as if the Prius is a moving truck or heavy loaded, semi-trailer truck. Long distance truckers have a vested interest in keeping their fuel costs down and when loaded, drive efficiently. Mostly, I drive on cruise control but when going up a good sized hill, 200 m. or so, I like to pull into any available truck climbing lane and let my speed fall off to ~90 km/hr (~55 mph.) Otherwise, I'm running around 105 kph (~65 mph) on cruise control. Bob Wilson
My trick when on cruise is to leave the cruise on but when I see a hill coming I accelerate on the approach before the cruise control sees the hill so I start the climb a little fast like 8 to 10 km/h over the limit then control the power to reach the top of the rise just as the cruise speed is hit then lift off and allow the cruise to take over until the next hill. I have no way to confirm but I believe this saves a little fuel and gets me there a little sooner.
thanks for the quick notes. it appears that cruise is not necessarily a hinderance. i am driving in southern alberta and it definitely seems it loves the flat terrain. i am mostly amazed that we are 1 pip down having gone 230 kms. i am sure this is not the average pip distance but pretty amazing nonetheless. i our old civic it would have taken us half a tank (15 L.) in town i have been averaging 50 km for each pip in stop and go traffic.
There is a reason that here on PriusChat the fuel guage is called the "guess guage". Don't expect to get 230 km per pip the seem to disappear at random intervals. To your original question. On flat terrain there is no reason not to use cruise control. The cruise control should be better than your foot because it will maintain a constant speed while humans tend to drift around a bit. In hilly terrain a human can do better than the computer as long as you are willing to let your speed vary. The key is that the cruise control computer has no idea how long a hill is. Many times I've had cruise control on and as I almost crest a hill the cruise kicks in a "floors" the accelerator to maintain the set speed. I've tested this on a 2 lane US highway with rolling hills. Driving with the cruise control set to 60 mph and got ~50 mpg. The next day I drove the same route but didn't use cruise. I used a "roller coaster" method where I allowed my speed to drop as low as 50 mph uphill and coast up to 70 mph downhill. This method resulted in ~60 mpg.
Another way to use cruise control climbing a hill is to drop the speed set point on the control just before the engine kicks in to keep the speed up. When you get on the down side push the speed up slowly with the foot control watching the instant read out and then reset the set point when you get to the speed you want.
