Best Highway Cruising Speed for MPG's

[stratosurfer]

I am easily getting over 40 MPG in city driving (hand calculated), yet when taking long Texas highway road trips when I must push 75 mph I only get 34.5 on the average. I have been trying to find a -magic- highway speed to get to my appointments on time and not waste efficiency. I don't seem to have found the sweet spot on this. I am in Texas Hill country primarily making continuous ups and downs and running lots of A/C lately. I have tried 68 MPH which seems to push me up to around 36.5 to 37 MPG's. I will also 'pedal shift' the car into e-mode on downhills, but I can get sloppy on this on 6 hour trips.

Anyone got a compromise speed they've found to get somewhere relatively fast. I cannot drive 55 MPH, I know this is where this vehicle shines, some places I drive out here the speed limit is 80... The semi-trucks are doing all of that.

Thanks

[Kelleytoons]

The "magic" speed is apparently 67-68 mpg, on Ecocruise.  If you can get it there (and turn the cruise on) you should be able to get in the 40's.

 

So if you were at 68 with the cruise on (must have the cruise on for this to work) try 67.  Folks swear by this method (I haven't tried it myself so I can't say it if really works or not).

 

Also, make sure you have recirc on your A/C -- that also apparently helps (I've gotten to the point now where I just leave it there).

Edited September 3, 2014 by Kelleytoons

[vmmvmmm]

it depends on so much, but I've found that if I'm between 65-70 on a flat highway without much of a headwind, I can get between 40-45 mpg pretty easily.  Not sure if altitude has to do with it as well, I'm at about 4500 ft.

[ptjones]

OK, so I did it on my 5K trip to San Diego and back.  I did it between Flagstaff,AZ and Amarillo,TX with two stops in Gallup,NM and Albuquerque,NM and made the 500mi. around San Juan,NM. I have New Michelin's on the car and Odometer is off by 1.019% according to Garmin GPS. Actual numbers are for mileage(512mi), speed(66MPH) and 47.1mpg for the whole tank and looks like 47.3mpg for 500mi.

 

Here is how I did it, I used a banking system where I would save MPH and MPG.  So if MPH got low I would trade MPG for MPH.  I used Garmin to track MPH average and Smart Gauge to track MPG average. I took I-40 all the way to Memphis,TN.  The elevation drop from Flagstaff to San Juan is about 3,000Ft, but there are three over 7K ft. summits  between the two city's.  Starting about 2PM in the afternoon from Flag with the plan that I should be able to bank both MPG's and MPH's going down to Winslow(50mi. and 2K ft drop), but things went  BAD quickly with two different problems.  Rain and Semi's, as it turns out it rained at least 1/3rd of my trip and had to deal with alot of Semi's, easily half of the traffic on I-40.  Rain hurts both MPG's and MPH's and you can't draft Semi's in the rain if you want to see where you are going.  On the other hand being forced to follow Semi's while they are passing each other helps MPG's but kills MPH's.  So By the time I got to Winslow things where looking BAD, instead of having alot of extra MPG's and MPH's  banked,  I was already short with 45mpg, 67mph, I almost gave up not seeing how I could make up the deficit.  Then things started to improve, the rain stopped and I was able to start passing Semi's and get some drafting help while I was waiting to get around them. Then about 40mi. later the winds changed from cross wind to tail wind so then the numbers were getting better.

 

I stopped in Gallup, NM with about 67.5mph and 47.5mpg, but with stopping and getting going again I lost 1 mph on the Garmin, worse on Smart Gauge.  OUCH! Then I hit rain again and winds stopped, still I was ahead of the game when I got to Albuquerque. Lost .5mph for that stop and hit rain again, but not to bad. Eventually I just kept MPH average at 66 and aloud MPG's to slowly climb knowing Smart Gauge would be optimistic by a couple of MPG's.  Most of the time I was going 69-70mph when I wasn't stuck behind Semi's or in construction zones. You may have noticed my top speed on the Garmin was 81.3mph! This exercise shows that 500mi. is a long way to go without having weather and traffic problems. When conditions are favorable, my CMAX will get 47mpg at 70mph. :)   Paul     

Also I used P%G when I could, no ECO Cruise.

Edited September 3, 2014 by ptjones

[Kelleytoons]

So now, Strato, you have the superhuman approach, and the mere mortal one.  You *ought* to be able to figure out how to improve given all that info.

[ptjones]

I am easily getting over 40 MPG in city driving (hand calculated), yet when taking long Texas highway road trips when I must push 75 mph I only get 34.5 on the average. I have been trying to find a -magic- highway speed to get to my appointments on time and not waste efficiency. I don't seem to have found the sweet spot on this. I am in Texas Hill country primarily making continuous ups and downs and running lots of A/C lately. I have tried 68 MPH which seems to push me up to around 36.5 to 37 MPG's. I will also 'pedal shift' the car into e-mode on downhills, but I can get sloppy on this on 6 hour trips.

Anyone got a compromise speed they've found to get somewhere relatively fast. I cannot drive 55 MPH, I know this is where this vehicle shines, some places I drive out here the speed limit is 80... The semi-trucks are doing all of that.

Thanks

I travel through Texas's 80 mph speed quiet often and can get 42-45mpg drafting semi's. Winds are a problem out there though and can make a BIG difference in MPG's. Just recently I drove from EL Paso to Abilene on I-10 to I-20 and the first about 200mi. with tale wind  and drafting 80mph semi's, I was getting almost 50mpg :happy feet: , but then it all went down the tube. The Winds changed to strong cross winds and rain and I ended up with around 42MPG on that tank. :sad:

 

Paul

 

Paul

[plus 3 golfer]

it depends on so much, but I've found that if I'm between 65-70 on a flat highway without much of a headwind, I can get between 40-45 mpg pretty easily.  Not sure if altitude has to do with it as well, I'm at about 4500 ft.

Yes, air density is about 15% less at 4500 feet than at sea level.  So, the aerodynamic drag force on a car will be about 15 % less at 4500 feet  Based on Ford's  RLHP coefficients, I estimate that the 15% equates to about 10% reduction in HP required at the wheels at 70 mph at 4500 feet vs around sea level and as much as 10% better FE than those at sea level.  

 

Of course not everyone lives near sea level.  I would estimate that where I drive in the Valley of the Sun all other things being equal except elevation, that you would get between 3-4% better FE at 70 mph than I do because air is less dense at 4500 feet than in the Phoenix area.

[ptjones]

Air Temperature will also effect air density being a pilot it is very important consideration. :) 

 

Paul

[plus 3 golfer]

Yes, that's why I always say in cold weather after warm-up, lower ambient temperature in the winter increases air density and hence FE will drop considerably vs summer.  

 

Now add such factors as humidity, driving in rain and wind, "rough" roads, use of HVAC system, driving style, speed, tire pressure, aero and other mods, fuel, weight and so forth, comparing FE with someone else makes little sense and could vary significantly. 

 

stratosurfer, If one is using the tips and techniques on this site (assuming that there is nothing preventing all C-Maxes from achieving virtually the same FE under the same conditions), ones FE is what it is.  Then, one needs to decide how much time they want to give up to get better FE.  I've posted curves in another thread that show the C-Max road horsepower requirements vs speed.  Follow the tips and drive slower to reduce power requirements to the extent that extending time is not a burden and your FE will go up.  You may find an optimal speed above which your FE begins to fall off dramatically.  I don't know whether you've seen the curve below from cleanmpg.com. This is before the software upgrade that raised the EV speed from about 62 mph to 85 mph.  So, the back end of the curve above 65 mph might be a little higher.

 

Also, if you want to see what cleanmpg got when they hypermiled in the city scroll down to near the bottom of the above link. 

 

Edited September 4, 2014 by Plus 3 Golfer

[ScubaDadMiami]

I vote for 67-68 MPH. How do you have your A/C set? Turn off Auto, use recirculate, keep the temperature between 73-75F, maintain fan speed between 3-5 bars. If you use Cruise Control, make sure to use Eco.

 

Other than wind, with everything set as above, you should get between  40-43 MPG during a good outside temperature range.

[Adrian_L]

Golfer,

 

So the highway sweet spot is a myth?  From your chart it would seem that I'll get higher MPGs going 55 on the highway rather than 65. 

 

Adrian

[shinytop]

I have seen that sweet spot.  But the fly in the ointment is you have to be cruising on level ground.  Uphill or downhill quickly loses the sweet spot.  Even in the low rolling hills I have in NW Florida and south Alabama.  If your SOC is not at or near the top the sweet spot does not get you the 47+.  

Edited September 4, 2014 by shinytop

[kostby]

"Sweet Spot" is absolutely not a myth, but, yes, for high-Internal Combustion Engine mode you must have all 4 conditions:

1) Eco Cruise enabled

2) ~67-68mph

3) on nearly level ground, and

4) with a high State-Of-Charge in the High Voltage Battery

 

the digital 43.6mpg was the average for the trip thus far, but notice the 'instant' mpg indicator to the right registers higher

 

This was maintained over about a 7 mile stretch of road that rises and then falls a total of about 30 feet from start to finish, per GPS Visuallizer

 

The sharp changes at the beginning and the last 2 or so miles at the end are the on- and off-ramps to the businesses nearest the stretch of interstate highway

Edited September 4, 2014 by kostby

[ptjones]

Yes, that's why I always say in cold weather after warm-up, lower ambient temperature in the winter increases air density and hence FE will drop considerably vs summer.  

 

Now add such factors as humidity, driving in rain and wind, "rough" roads, use of HVAC system, driving style, speed, tire pressure, aero and other mods, fuel, weight and so forth, comparing FE with someone else makes little sense and could vary significantly. 

 

stratosurfer, If one is using the tips and techniques on this site (assuming that there is nothing preventing all C-Maxes from achieving virtually the same FE under the same conditions), ones FE is what it is.  Then, one needs to decide how much time they want to give up to get better FE.  I've posted curves in another thread that show the C-Max road horsepower requirements vs speed.  Follow the tips and drive slower to reduce power requirements to the extent that extending time is not a burden and your FE will go up.  You may find an optimal speed above which your FE begins to fall off dramatically.  I don't know whether you've seen the curve below from cleanmpg.com. This is before the software upgrade that raised the EV speed from about 62 mph to 85 mph.  So, the back end of the curve above 65 mph might be a little higher.

 

Also, if you want to see what cleanmpg got when they hypermiled in the city scroll down to near the bottom of the above link. 

 

Unfortunately this is old info which at the time a lot of us felt it was bias. They tried to drive a CMAX like a Prius and you don't get as good MPG's that way.  I don't think the graph is accurate from my experience. It seems like the graphs should be getting closer together, because of less aero drag. Also I just got 70.9mpg averaging 40mph over at least 150mi. so take 2mpg off Smart Gauge # giving 69mpg, then try to put it on their graph and it doesn't work . I  don't know how they figured out how to temperature compensate for a CMAX.  On one Smart Gauge Pic the temp was 37*F, that would hurt CMAX  by -7MPG's. It doesn't look like they even figured out how to come up with accurate numbers for the CMAX, It would have taken a lot  of time and  would not be easy to do. IMO :)

 

Paul

Edited September 4, 2014 by ptjones

[plus 3 golfer]

Golfer,

 

So the highway sweet spot is a myth?  From your chart it would seem that I'll get higher MPGs going 55 on the highway rather than 65. 

 

Adrian

 

What is highway "sweet spot". I always get better FE by driving 55 mph (high 40s low 50s) than 65 mph (low - mid 40s) round trip. ;)   On longer trips my sweet spot is around 4 mph above the speed limit. So, where I drive that means 74 - 79 mph to save time.  Some may drive 55 mph on back roads to save $.  Some may find that 67 mph yields the best balance between FE and time.

 

IMO, what people see is that one can drive the car in "negative split" mode when the HVB SOC is about 56+ % (not the same as the battery symbol indicator).   This has the effect of slowing ICE rpm down (like lugging ICE in a conventional transmission by shifting to a higher gear or remaining in the higher gear and not downshifting thereby improving engine efficiency - low rpm, higher torque generally means a more efficient point on the BSFC).  The problem is it is hard to stay in this mode very long as any change in load requirements could trigger EV operation up to 85 mph or increased ICE rpm above an efficient point on the BSFC.  

 

Once ICE has reached it's most efficient operating range, any increase in speed adds more drag with likely no additional efficiency gain regardless of operating mode That point is likely around 67 mph on a flat road as running higher than that appears to be where the rate of drop in fuel economy seems to increase for many including myself.  Hence, 67 mph may be a good balance between time and FE.  As I've said many times if one can anticipate conditions, one can vary their speed (which the eco-cruise algorithm does to some extent) around the 67 mph mark  to increase FE even further.   Also,a slight downhill can increase the FE significantly in this mode. So, any testing needs to be done in both directions.  That presents a problem as the load / speed relationship has changed and it may not be possible to run in this mode in both directions.   In various testing / recording of data I've done, a 30 feet per mile of elevation change (which looks flat) can yield 50+ mpg going downhill and below 40 mpg going uphill for an average in the low 40s round trip. 

 

 

Negative Split Mode

 The engine is on and the generator motor

consumes electrical energy to reduce engine

speed

 The traction motor can operate as a motor or a

generator to make up the difference between

the engine power and the desired power

 Typical highway mode

 Occurs when the engine needs to be on, the

system can not be operated in parallel mode

and the battery is charged near its upper limit

 

 

Here's a graph from recording real time data that I posted before.  The graph shows a stretch of about 4 miles where I set the Eco-cruise to 55 mph where the car was in negative split mode.  SOC leveled out to about 58%, rpm fell to just above 1500 rpm, FE averaged about 47 mpg (purple line ending about time stamp 1200) into a sustained 10 mph headwind and about 10 feet / mile elevation increase. I'd probably been in the mid 50s with no headwind and elevation change.  I'd love to run all sorts of "controlled" tests and record the data but I don't have a "flat test track" with no other vehicles around and it simply takes to much time to do it correctly. :)

.

[Adrian_L]

Thanks for that.  I agree it would be interesting to see flat-road tests at various speeds.

[C-MaxSea]

I am easily getting over 40 MPG in city driving (hand calculated), yet when taking long Texas highway road trips when I must push 75 mph I only get 34.5 on the average. I have been trying to find a -magic- highway speed to get to my appointments on time and not waste efficiency. I don't seem to have found the sweet spot on this. I am in Texas Hill country primarily making continuous ups and downs and running lots of A/C lately. I have tried 68 MPH which seems to push me up to around 36.5 to 37 MPG's. I will also 'pedal shift' the car into e-mode on downhills, but I can get sloppy on this on 6 hour trips.

Anyone got a compromise speed they've found to get somewhere relatively fast. I cannot drive 55 MPH, I know this is where this vehicle shines, some places I drive out here the speed limit is 80... The semi-trucks are doing all of that.

Thanks

 

Stratosurfer, I just wanted to say that what Kelleytoons said way up top here is correct that 68 mph, "on Ecocruise .............and you should be able to get in the 40's." easily.  What is important is that you use the ECO cruise option (although I suspect simple cruise would be almost as effective).  It is just that simple, ECO Cruise allows the car to select the best mode for gas mileage as the hills dictate.  As you increase the vehicle speed from there, the aero drag will have significant effect on gas mileage (but nothing wrong with 70 mph & 43 MPG on cruise). For 70mph and beyond you might want to talk to PTJones here about aeromods, definitely a good way to make improvements for higher speeds.

 

We are easily able to ECO Cruise freeways at 68 mph and get 45-50 mpgs on the dash gauge over longer looped freeway runs.  We have not seen 45 since last Winter.  Your Texas weather & winds (& excessive AC) will crunch your numbers some of the time, but with quiet, temperate air it is easy to move into the low 40s at 70 mph (or higher 40s if you want to back off the speed just a smidge), the better part of the year, if you just use the ECO Cruise. ((Or just talk to PT))

 

Cheers,

Nick

 

(Last trip 460 looped miles, 2,200 ft. elev. difference, highway/freeway speeds 60-68, minimal 'city', 50% AC, 48.6 MPG (47 at the pump) - no sweat !!! )

(OK, we sweated a little bit)  (and always paced with the traffic flow; above, at or just under the speed limits - no geriatric driving)

Edited September 5, 2014 by C-MaxSea

[John Sparks]

Stratosurfer, I just wanted to say that what Kelleytoons said way up top here is correct that 68 mph, "on Ecocruise .............and you should be able to get in the 40's." easily.  What is important is that you use the ECO cruise option (although I suspect simple cruise would be almost as effective).  It is just that simple, ECO Cruise allows the car to select the best mode for gas mileage as the hills dictate.  As you increase the vehicle speed from there, the aero drag will have significant effect on gas mileage (but nothing wrong with 70 mph & 43 MPG on cruise). For 70mph and beyond you might want to talk to PTJones here about aeromods, definitely a good way to make improvements for higher speeds.

 

We are easily able to ECO Cruise freeways at 68 mph and get 45-50 mpgs on the dash gauge over longer looped freeway runs.  We have not seen 45 since last Winter.  Your Texas weather & winds (& excessive AC) will crunch your numbers some of the time, but with quiet, temperate air it is easy to move into the low 40s at 70 mph (or higher 40s if you want to back off the speed just a smidge), the better part of the year, if you just use the ECO Cruise. ((Or just talk to PT))

 

Cheers,

Nick

 

(

 

I agree with this. I live in East Tennessee and we have plenty of hills, ridges, mountains, etc. At 66-68 mph 50 mpg is not uncommon. At 70mph I see 42-45 and at 75mph 39-43. Depends on how hot it is and how much more the air has to work. I still say Ford was spot on with they're first revision. With the latest revision it might as well say: "Drive this car however you want and you will get this mileage". My wife drives it from time to time and she doesn't even try to get good MPGs and usually comes out around 43. She's impressed with the car, so much were even considering leasing an Energi.

[ptjones]

I want to clear up any possible confusion, ECO Cruise is the easy way to get good MPG's at HWY speeds, but Hypermiling(Drafting, P&G and etc.) gets higher MPG's. Aeromods are worth another 3-4mpg's. :)

 

Paul

[Testdriver]

These are my estimates of the MPGs I get in my CMax at cruising speeds over long distances:

 

25 MPH - 65 MPG

35 MPH - 60 MPG

45 MPH - 55 MPG

55 MPH - 48 MPG

65 MPH - 42 MPG

70 MPH - 38 MPG

75 MPH - 35 MPG

 

So, if you want to achieve max MPG, slower is almost always better.

[Adrian_L]

Thank you.  Personally, I was looking for the highway speed that produces the best mileage in all conditions. 

 

I'll continue to drive like a geriatric--i.e. 55 on the highway. 

[C-MaxSea]

Testdriver, our C-Max is one of the magic ones (every 3rd or 4th off the line, I guess) because it easily exceeds your 'highway' numbers by 5 MPG.   ;)

(all subject to .........................)

 

Dozens of times we've driven to the freeway with 38 to 42MPGs showing for those 5 miles with about a 100' elevation gain and ICE warm up;  once on the urban interstate our C-Max religiously climbs to 45-50 MPGs by the 25 mile post with 60 mph speed limits (we drive at 58-62+- mph subject to traffic),  continuing with an elevation drop of around 200 feet our C-Max climbs to between 50-55 MPG at 30+- miles;  continuing, with elevation regains, the MPGs settle in at 45-50, and will go 'forever', including when the speed limit increases at about 40+-miles to 70mph, and we settle in at 68 mph .....................................100, 200, 300, 400, looped miles.  (last loop, 460 miles, 48.6 (47) MPG with a 2000' elevation gain)  Happy we got a magic one.   

 

From "Never-Never Land" (Googieville, Seattle),

Nick

 

(Crux:  letting the car 'drive itself' in ECO Cruise on the freeway, with only a little toggle play for fun! (Don't forget to steer!)

Edited September 7, 2014 by C-MaxSea

[Jus-A-CMax]

You all want to keep the battery SOC high, eco-cruise tends to drain the batts when it thinks it has too much so....a quick tap of the accelerator will put the car back into ICE mode where it will siphon or continue to build the high SOC, all while your Instant MPG should dance around 40 to 45, or more if there is a slight incline....

 

This was so much better before 13b07 thanks to the EV limit. Ah, get one thing and lose another....*sigh*

[C-MaxSea]

We are in hilly terrain most of the time, so we allow the car to 'cycle' the battery constantly in ECO Cruise, ignoring the state of charge, other than for opportunistically taking it down or juicing it up a wee bit occasionally.  100 ' up, 150 ' down, 250' up, 100' down..............on our freeway driving.  Only rarely do we see flat stretches where the car chooses negative split.  We allow it to do negative split, but do not see any improvement from it (may be a detriment???) - now flat highways elsewhere might be a different story.  But what's to complain about getting 48 MPGs at 68 mph?  I believe we are 'topping out' on our MPGs, can't see any way higher on the freeway without mods.  Gen 2 C-Max will be required to take us over the 50 mark - unaided.    (BTW, we did not run up enough miles before 13b07 to see significant differences, so I'm a wee bit of a skeptic on the 'good old days' - too much work forcing sauce any way). ECO Cruise forever (with a wee bit of toggle for fun) !!!

 

Nick

 

(Thinking we will continue unaided until January in order to have 2 full years logged (70-80 % 'highway'/'freeway' miles), then send a check to Paul  :))

 

((BTW  Happy birthday to Grouper (otherwise known as Starship GG), he turned 2 in August !!!))

Edited September 6, 2014 by C-MaxSea

[ptjones]

We are in hilly terrain most of the time, so we 'cycle' the battery constantly, ignoring the state of charge, other than for opportunistically taking it down or juicing it up a wee bit occasionally.  100 ' up, 150 ' down, 250' up, 100' down..............on our freeway driving.  Only rarely do we see flat stretches where the car chooses negative split.  We allow it to do negative split, but do not see any improvement from it (may be a detriment) - now flat highways elsewhere might be a different story.  But ((((((((((((((what's to complain about getting 48 MPGs at 68 mph? ))))))))))) I believe we are 'topping out' on our MPGs, can't see any way higher on the freeway without mods.  Gen 2 C-Max will be required to take us over the 50 mark - unaided.    (BTW, we did not run up enough miles before 13b07 to see significant differences, so I'm a wee bit of a skeptic on the 'good old days' - too much work forcing sauce any way). ECO Cruise forever (with a wee bit of toggle for fun) !!!

 

Nick

 

(Thinking we will continue unaided until January in order to have 2 full years logged unaided (70-80 % 'highway'/'freeway' miles), then send a check to Paul  :))

 

((BTW  Happy birthday to Grouper (otherwise known as Starship GG), he turned 2 in August !!!))

Where is your 500mi. 47mpg, 65mph trip?  No Drafting.LOL :)

 

Paul