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I did some testing today. My conditions aren't the best because I really don't have a truly flat area to test in. Traffic was moderate but I did not have to accelerate or slow down at any point during my tests so the speeds were truly constant. That said, because traffic patterns varied during each test it's hard to rule out wind / turbulence generated by other vehicles. But it's the Bay Area, so unless I go out at like 3am or on Christmas morning it's almost impossible to get the roads all to yourself.

Testing temperature was stable at 59 degrees F throughout the test. ScanGauge reported atmospheric pressure at 14.5 psi (again, constant through the test). Wind seemed minimal, but I did not have real-time measurements. The overall run distance was just under 10 miles each way and runs were conducted in both directions back to back. Starting point elevation was about 88 m / 288 feet and ending point elevation was about 128m / 420 feet. The terrain had very light elevation rises and falls throughout, but there were definitely no major grades to tackle either way. Cruise control was used for all runs and the trip computer was reset and read at the same location every time (obviously with sufficient time / distance on both ends of the run to get up to speed before starting observations).

I have just under 4,000 miles of logged data and trip computer reported MPG. My trip computer error is approximately 3.5% optimistic based on that data.

Here's the basic data with southbound MPG followed by northbound MPG:

55mph run 1: 45.5 / 48.3
55mph run 2: 46.2 / 47.3
55mph average: 46.825
Corrected average: 45.172 MPG

65mph run 1: 40.4 / 39.3
65mph run 2: 42.1 / 39.6
65mph average: 40.35
Corrected average: 38.926 MPG

These numbers square well with what I would have projected based upon the data for the NX 300h and RX 450h found at the CleanMPG forum. If you take the data found there and extrapolate it to the RAV4 you'll see the curves are a pretty clean fit even though I only have 2 real data points. It's also closer to the NX curve than the RX (as we might expect). It's certainly not exact, but it is validating that the data I've captured seems to be reasonable and in line with what we might expect to see. Based on those curves, I would expect the following (approximately) assuming I had time to keep testing all these speeds all day:

50mph: 47.35 MPG
60mph: 41.94 MPG
70mph: 34.66 MPG

Here's the thread with the raw data from CleanMPG if you're interested (along with a bunch of other vehicles): Steady State Speed vs Fuel Economy results | CleanMPG

One thing I noticed is that at 55mph, my N/B run was actually more efficient than my S/B run whereas at 65mph the reverse is true. I believe (based on my observations of my ScanGauge) that the system is able to more efficiently put the battery to use at 55mph because the power requirements were low enough during certain sections that I was able to see some "power gliding", I'll call it. Basically RPMs were at idle and M2T (MG2 torque) and AMPs (HV battery amps) were positive, meaning that MG2 was drawing off the battery to maintain speed instead of taking power straight off the ICE. At 65mph I saw barely any of that happening. So however the conditions played into this test, clearly the system can be even more efficient at lower speeds than just the aerodynamics alone may allow for.

I also did a 65mph run without my grill blocking pipe insulation and the results were interesting: 40.0 / 40.7
So, an average of... 40.35 MPG (uncorrected) - the exact same as I got with the grill block in place. What does this really tell us? Well, that's a little harder to say since there are a lot of variables affecting MPG in the real world. But it doesn't seem that my grill block is making much difference in terms of aerodynamics. There are certainly thermal management reasons to use it, but I'm not seeing the gains that other people have reported with grill blocks and aero benefits. Now, the pipe insulation is somewhat flexible and it's entirely possible that at those speeds it is deforming enough to let air through. I have no way to look at it while I'm driving, obviously. It would be interesting to see some numbers from anyone who has truly made a nice custom grill block like some of the Prius folks have done.

Hope that helps... and as always, YMMV... :wink
 

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Your info backs up what I wrote in another post

I did some testing today. My conditions aren't the best because I really don't have a truly flat area to test in. Traffic was moderate but I did not have to accelerate or slow down at any point during my tests so the speeds were truly constant. That said, because traffic patterns varied during each test it's hard to rule out wind / turbulence generated by other vehicles. But it's the Bay Area, so unless I go out at like 3am or on Christmas morning it's almost impossible to get the roads all to yourself.

Testing temperature was stable at 59 degrees F throughout the test. ScanGauge reported atmospheric pressure at 14.5 psi (again, constant through the test). Wind seemed minimal, but I did not have real-time measurements. The overall run distance was just under 10 miles each way and runs were conducted in both directions back to back. Starting point elevation was about 88 m / 288 feet and ending point elevation was about 128m / 420 feet. The terrain had very light elevation rises and falls throughout, but there were definitely no major grades to tackle either way. Cruise control was used for all runs and the trip computer was reset and read at the same location every time (obviously with sufficient time / distance on both ends of the run to get up to speed before starting observations).

I have just under 4,000 miles of logged data and trip computer reported MPG. My trip computer error is approximately 3.5% optimistic based on that data.

Here's the basic data with southbound MPG followed by northbound MPG:

55mph run 1: 45.5 / 48.3
55mph run 2: 46.2 / 47.3
55mph average: 46.825
Corrected average: 45.172 MPG

65mph run 1: 40.4 / 39.3
65mph run 2: 42.1 / 39.6
65mph average: 40.35
Corrected average: 38.926 MPG

These numbers square well with what I would have projected based upon the data for the NX 300h and RX 450h found at the CleanMPG forum. If you take the data found there and extrapolate it to the RAV4 you'll see the curves are a pretty clean fit even though I only have 2 real data points. It's also closer to the NX curve than the RX (as we might expect). It's certainly not exact, but it is validating that the data I've captured seems to be reasonable and in line with what we might expect to see. Based on those curves, I would expect the following (approximately) assuming I had time to keep testing all these speeds all day:

50mph: 47.35 MPG
60mph: 41.94 MPG
70mph: 34.66 MPG

Here's the thread with the raw data from CleanMPG if you're interested (along with a bunch of other vehicles): Steady State Speed vs Fuel Economy results | CleanMPG

One thing I noticed is that at 55mph, my N/B run was actually more efficient than my S/B run whereas at 65mph the reverse is true. I believe (based on my observations of my ScanGauge) that the system is able to more efficiently put the battery to use at 55mph because the power requirements were low enough during certain sections that I was able to see some "power gliding", I'll call it. Basically RPMs were at idle and M2T (MG2 torque) and AMPs (HV battery amps) were positive, meaning that MG2 was drawing off the battery to maintain speed instead of taking power straight off the ICE. At 65mph I saw barely any of that happening. So however the conditions played into this test, clearly the system can be even more efficient at lower speeds than just the aerodynamics alone may allow for.

I also did a 65mph run without my grill blocking pipe insulation and the results were interesting: 40.0 / 40.7
So, an average of... 40.35 MPG (uncorrected) - the exact same as I got with the grill block in place. What does this really tell us? Well, that's a little harder to say since there are a lot of variables affecting MPG in the real world. But it doesn't seem that my grill block is making much difference in terms of aerodynamics. There are certainly thermal management reasons to use it, but I'm not seeing the gains that other people have reported with grill blocks and aero benefits. Now, the pipe insulation is somewhat flexible and it's entirely possible that at those speeds it is deforming enough to let air through. I have no way to look at it while I'm driving, obviously. It would be interesting to see some numbers from anyone who has truly made a nice custom grill block like some of the Prius folks have done.

Hope that helps... and as always, YMMV... :wink
You lose approximately 3 mpg for every 5 mph increase in speed : )

I havent tried the grill block. Nights here are about 50 and days about 70ish.
 

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Discussion Starter #5
Considering that air resistance is the largest factor, and air resistance = speed^3, that statement can't hold true for more than one span of 5mph. :D
I agree... it’s not a bad approximation between 55 and 65. But from 65 to 70 I would expect to see closer to a 4mpg drop and it goes downhill pretty quickly from there.

Additionally, with the way the hybrid system works and is “geared” I would not expect to get 3mpg more at 50mph vs 55mph. Looking at the data from CleanMPG pertaining to all of the non-Prius Toyota hybrids (and my own anecdotal observations without hard numbers), I only expect about a 2mpg bump by slowing down to 50mph and actually worse mileage below 45 if you’re talking purely steady state driving with the ICE and not including EV gliding.
 
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It is what it is...

Considering that air resistance is the largest factor, and air resistance = speed^3, that statement can't hold true for more than one span of 5mph. :D
Im getting about 39 mpg. I average about 65-68 on the hwy with some as high as 85 going down hills. Quite a bit of stop & go when Im doing local driving. I did notice that when you go below 50 mileage goes down. I will take this mileage any day but it would be nice to get over 40. I already get people cutting me off because I dont drive fast enough for them, southern californians generally dont know how to drive.
 

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Im getting about 39 mpg. I average about 65-68 on the hwy with some as high as 85 going down hills. Quite a bit of stop & go when Im doing local driving. I did notice that when you go below 50 mileage goes down. I will take this mileage any day but it would be nice to get over 40. I already get people cutting me off because I dont drive fast enough for them, southern californians generally dont know how to drive.
That's a good average! Getting up to 65 is a miracle around here more often than not with as heavy as traffic in the Bay Area is these days. Gives me a lot more opportunity to glide, but I'd still be better off if I were able to maintain consistent speeds more regularly. Good luck!
 

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That's a good average! Getting up to 65 is a miracle around here more often than not with as heavy as traffic in the Bay Area is these days. Gives me a lot more opportunity to glide, but I'd still be better off if I were able to maintain consistent speeds more regularly. Good luck!
My front grill is almost blocked at 100% (almost 100% lower , except where the sensor is and 75% upper), but with cold temperature (not that much IMO), snow tires, Thule cargo box on top, some hills, and about 110 km/h on highway, it's very hard to get better than 8,5L/100 (28 MPG?).
@MTL_Sienna What should I expect in january when temperature will drop?
 

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My front grill is almost blocked at 100% (almost 100% lower , except where the sensor is and 75% upper), but with cold temperature (not that much IMO), snow tires, Thule cargo box on top, some hills, and about 110 km/h on highway, it's very hard to get better than 8,5L/100 (28 MPG?).
I did not see an aerodynamic benefit from the grill block during my testing. Granted I don't expect there to be a huge benefit so it's quite possible that the true results were simply masked by the "noise" in the testing data since I can't have exactly perfect conditions on each run. But I do expect that the grill block will help maintain engine bay temps and allow for more consistent EV use, etc. I just don't know what it's real effect is at highway speeds.

As a (very general) rule of thumb, air density climbs about 2% for every 10 degree F drop. My testing was done at 59 degrees F. So if your temperatures are closer to 30 degrees, say... I would estimate that your fuel economy at freeway speeds would decrease by approximately 6% relative to my numbers due to aerodynamic drag alone. And it goes down from there as temperatures drop further. This is assuming you hold humidity, elevation, vehicle setup, and all other variables constant.

Your mileage is not necessarily surprising given the combination of factors working against you. The cargo box and roof rail cross bars definitely add quite a bit of drag which will be especially noticeable at freeway speeds. Then with your high traction tires and the cold temperatures, I'm sure it all adds up! Now whether or not it should be adding up to a full 25% drop by themselves is another story... Perhaps the hills are also a big issue?

I think hills have more of a detrimental effect on our fuel economy than they might in a non Hybrid Synergy Drive (HSD) vehicle. This may also be a significant source of your relatively low fuel economy average. I could be entirely wrong, of course, but this is my take:

I don't find the hybrid powertrain to be the most efficient on hills (going up them anyway). I have noticed that on steeper grades, like certain sections of Interstate 80 climbing from Sacramento to Donner Summit at 65mph (a total of about 7000 feet in elevation gain), I'll get the engine running north of 4000 rpm (usually pretty close to its torque peak) just to maintain speed. With a couple of my previous ICE-only vehicles (2004 Ford Ranger - 2.5L / 140hp / 3000 lbs and 2012 Mazda 5 - 2.5L / 150hp / 3500 lbs), I'd definitely have to downshift on those same grades, but I would generally not need to rev it that high. Running an ICE at near WOT (but still in closed-loop operation) at lower RPMs should be more efficient than doing the same at higher RPMs if simply because you're not burning as much fuel in the process with the engine turning over slower while still minimizing pumping losses.

I think the issue with the RAV4h is that (1) it weighs a lot relative to its size and (2) the HSD doesn't have traditional gears to help with torque multiplication. The HSD uses MG1 to vary the speed at which the ICE can spin allowing it to rev up and down independent of vehicle speed and provide more or less engine torque as required. But in the end (the way I understand it), we don't have the traditional multiplication that a lower gear could give thereby allowing the ICE to output less at the crank and get the same net result at the wheels. (I realize we do have a final drive and so forth, but there's no way to further increase the torque multiplication before the power gets there.)

To better explain with an example (using totally made up numbers)... If you need 100 lb-ft of torque at the wheels, you could do it 1 of 2 ways:

(1) Get 100 lb-ft from your engine at a 1:1 ratio and put it to the wheels
(2) Get 50 lb-ft from your engine but use a 2:1 gear ratio to get that 100 lb-ft of torque at the wheels, but at half the speed

As I understand it, the HSD really only has the ability to provide power the first way and not the second. This is why we have the very large electric motor that is MG2 (plus MGR) - to fill in those torque gaps by acting as a gas-electric powertrain (similar to the way a diesel-electric locomotive operates). The engine is providing the power as a generator to spin the electric motor instead of directly putting power through the driveshaft. The HSD is obviously more complex and can drive the vehicle directly at higher speeds, of course. But my point is that using the engine as a generator to fill in torque gaps is likely less efficient than driving the wheels directly under high load operation. If nothing else, there are certainly losses when converting the ICE energy into electricity. So perhaps if your drives involve a lot of uphill grades, that's a large factor in your average economy.

Again, this is all based on my somewhat basic understanding of the HSD and my own personal observations, so take this as an anecdotal theory... :wink
 
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According to my experience the best road for the R4H to get the best MPG difference compared with normal car is medium hill roads with the elevation differences less than 300 ft. And when there is need to climp up not more than 1 miles distance and again driving down some miles. During driving down the battery will be fully loaded and while driving up the car can get full gain of the energy stored in the battery. The most difficult are the flat roads at high speed for R4H to get any gain of the hybrid system. In the cities and on the low to medium speed roads I can get the best MPG.
 

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Can you expand on that? :D


The power needed to overcome the drag resistance going from 100 to 200 is 2^3 (cubical) or 8x more. But the energy consumption (gallons of burned fuel for example) is only 8/2 because you arrive twice as fast or alternatively you consume that power for half as long, thus the formula becomes 2*2*2/2 which can be simplified as 2*2 or 2^2.

Note there was nothing wrong in your original statement, I just wanted to highlight this because both ^2 and ^3 is often misused/badly explained when it comes ti this topic.
 

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Figures in the OP are consistent with what the car magazines have published over the years.

In our 2400 round trip drive to Florida last winter, we average 31.6 mpg and that was 95% highway driving at posted limits (65-70) with a fully loaded cargo space. In 1300 miles of local Florida city/suburban (and some highway) driving, we averaged 39.1 mpg which is much better than we at home in Indiana.
 
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