I would like to know what your experiences with and without cruise control on. In my v5, it is very much improved whenever the cruise control is in use. This is typically a 5 to 10 mpg difference.
Constant speed does not necessarily net the best mileage unless on a flat surface where it would mean constant power. Learn to maximize mpg based on power needs for the moment and what's ahead, not just the easiest way. This is hypermilling.
Even on highways with steep grades like the Palisades Parkway and the Henry Hudson Parkway around New York City, I find that using cruise control results in much better MPG. The cruise control system on the Prius actually seems to be much better at maintaining a constant speed under such conditions than what I observed in my V6 Camry. The only problem with using cruise on these roads is that other drivers seem to drive with a constant throttle position: they slow down on ascent and speed up on descent.
Even on highways with steep grades like the Palisades Parkway and the Henry Hudson Parkway around New York City, I find that using cruise control results in much better MPG. The cruise control system on the Prius actually seems to be much better at maintaining a constant speed under such conditions than what I observed in my V6 Camry. The only problem with using cruise on these roads is that other drivers seem to drive with a constant throttle position: they slow down on ascent and speed up on descent.
Again, constant speed does not net the highest mpg if you drive hypermill style. Accelerating down hills and coasting up, or powering up and coasting down will get you the best because the engine can turn off or supply close to no power for a durration resulting in really high mpg for that section. Added over time it helps greatly.
It really depends on the driver in other words. Some people can beat the cruise control & others just don't want to work that hard. I tend to leave it on for all but the most hilly stretches of highway. Or going up a longish hill I'll slowly step it down one click at a time to avoid the engine straining to maintain 65mph. Ending up at around 55mph at the top of the hill, then use the downhill side to regain the speed for free. Traffic considerations can throw all that out at any time. - D
I agree with all of the above re flat terrain. I frequently drive over a mountain pass, and I normally use cruise control on the assent, but coming down, I take it off cruise, and hypermill enough to keep the HSI in the "sweet spot." That seems to work best for me.
A good example of cruise control inefficiency is exhibited when driving on a relatively flat road with very small and short elevation gains. The cruise control will try to accelerate up this tiny uphill section then reduce or maintain speed down the other side. This causes a larger fluctuation in mpg than if you had simply maintained a consistent throttle input while going uphill then regained your lost speed down the other side. Keep in mind I'm not talking about real hills. I'm focusing on small undulatiions of maybe 5-10 ft that occur on most roadways.
A bit apples/oranges since we've got a regular Prius, but assuming they're similar: I used to be negative towards using Cruise Control, found I could get better numbers without. But I've found the Prius CC pretty efficient: at least on relatively level roads my ScanGuage shows very good instant mileage.
And make sure it's flat. A slight elevation gain over a few hundred miles will make a difference. (200 mile trip with a 1,250ft difference got me 46.1mpg going one way but the return trip back down brought it up to 50mpg with the cruise control). I tried the same 200 mile trip (one way so I'll be basing it on 46mpg) without CC and it got me 52.3mpg.
Ok…well I just took a trip from Pittsburgh to Martinsburg WV. I didn’t use cruise control on the way there and I used it on the way back. This is what I discovered on my 210 mile trip (each direction). Without cruise control (up and down mountains, with slowing and speeding Thanksgiving traffic)-- 40.2 mpg With cruise control (same environment)-- 39.8 mpg (and that could is just too close to call) I had the cruise control set at about 75mph the entire way, which is about what my speed was going too.
Dragon, is that calculated by the computrter or did you fill the tank and divide gallons by miles? I ask because both those numbers are right on the epa highway number, except the epa doesnt test at 75 mph, which is good news. But if thats readings from the cumputer then thats probably inflated about 1.5 mpg.
Below 41 MPH (gen 2) I find the computers 'trust' the Cruise Control more than they do me. I get way better mileage in Cruise. (but my terrain is dead flat)
Your MPG is impressive considering I only get maybe 44 MPG on my 2006 for similar trip to the 'Burgh, given the mountains. Now then Pgh is probably 1500-ft elevation, so suspect you are downhill outbound.
A factor to be considered in all this is traffic. In heavy traffic, I wouldn't use the cruise control. I need to have better control of my speed alterations when necessary. Also, following drivers could be aggravation at frequent changes in speed such as up and down hills. In light traffic on regular terrain, I find best success w/o cruise.
