Speed vs. Fuel Economy - 2004 Chevrolet Aveo sedan (1.6 L, 4-sp automatic)
 

As an experiment for one of my college courses, I decided to test how speed affects fuel economy. This was a fun experiment as I was able to confirm other graphs made with different cars

Here is my data:
Temp: 69F
Pressure: 30.29"
Avg Wind Speed: 2.53 mph
Road Length: 0.85 miles, slightly inclined

Speed(mph) South(mpgUS) North(mpgUS) Average(mpgUS)
__________________________________________________ _______
25-------------38.5-------------40.5-------------39.5
30-------------40.3-------------43.3-------------41.7
35-------------41.2-------------45.6-------------43.3
40-------------40.1-------------47.0-------------43.3
45-------------38.7-------------45.1-------------41.7
50-------------41.5-------------46.7-------------43.9
55-------------38.9-------------42.0-------------40.4
60-------------36.2-------------38.5-------------37.3
65-------------33.7-------------37.2-------------35.4
70-------------32.8-------------35.1-------------33.9

There you have it. A few things to note: My fuel economy stays relatively the same between 30 and 55 mph. I have a 4-speed automatic transmission, and my car was in third at 45 mph (I don't like how my car doesn't shift earlier). At 50 mph is where I was at the lowest rpm range in the highest gear, hence the jump in fuel economy from 45-50 mph. Looking back on it, I wish I would have done 20 mph and 75 mph runs (possibly higher speeds too) to see a decrease in fuel economy at both ends.
One final note: I acheived 46.4 mpg on the 13.4-mile (starting from a stop and ending with a stop) drive back from the test road. I used pulse and glide between 60 and 45 mph.:thumbup:

My art student self tried to use Excel for the first time in about 8 years. Here are the results. Better than nothing? It would be great to get a few more runs for more consistent numbers but you can still see a general pattern.

http://i42.tinypic.com/2r4oeqc.jpg

Edit: can someone who knows what they're doing make a better graph please? I swear this would be 10x better if I did it by hand on graph paper. :(

Start by getting your data into two adjacent columns, with MPH in the left column and average MPG in the right column. Then select the data and insert an X-Y or scatter (two names for the same thing) chart.

Yeah, give me a few minutes and I'll throw one together.

Edit: Let's see if this works:

http://img.photobucket.com/albums/v4.../SpeedtoFE.jpg

I wonder what's the cause for the squiggle in the MPG graph in post #5.
In reality its not all that big, ~2 MPG, ~5%.

It could just be the result of it being only a single data run.

But I can accept that it happening just as the graph turns downward
may be more than just coincidence.

A +1 MPG adjustment at 45 MPH and a -1 MPG adjustment at 50 MPH would
show what I would consider to be a much more likely MPG graph.

Would access to a BSFE chart shed light on whats going on?

An inquisitive but semi-informed mind would like to enquire. :o

Yeah, you're probably right. Just minor noise. It has probably been compounded by the graph's close zoom, but I wanted the text to be big.

Additionally, I think it may have something to do with what Aveomiler observed about the OD not kicking in until 45mph.

He's in third gear up through 45 MPH. I'd like to know if the torque converter was locked up in third gear.

My wife's PT Cruiser had a four speed automatic. The torque converter would lock up in third gear if it was manually shifted to third gear.

Yeah my car stays in 3rd gear too long. At 45 it was in 3rd so my gas mileage dipped a little. I did another run at 50 mph with my car in 3rd gear instead of 4th to see the drop in mpgs. I got under 40 mpg for that run. I would really like it if my car would let me shift a little after 40 mph because I think I would be able to get great gas mileage at that speed.

Thanks Kodak for that graph. Aveo, does your car have manual mode? That could be very useful.

Also, I'm kind of disappointed at the EPA for GM's "economy" car- combined is only 2MPG better than the Probe. You'd think it would be more eco-minded! :(

I can select and hold my car in 1st, 2nd and 3rd gears but I can't hold it in 4th if I go under the speed that it's supposed to shift at (I can't upshift early).:mad:

Although since I am able to select and keep 3rd gear, it might be more fuel efficient to shift into 3rd earlier than it normally would as I'm accelerating. I've recently been getting used to "foot-shifting" my car into the gear that I want, but maybe I should try using the gear lever too.

As for your other comment about GM's "economy" car, I agree. The 2004 Chevy Aveo was sold having the worst fuel economy in its class. It kind of makes me frustrated when I tell people that my best tank was 34 mpg doing combined driving, and they aren't the least bit impressed because that's what they expect my car to be able to do. Maybe people will start paying attention when (if) I start getting 40 mpg (Time to work on the aero mods).

OTOH, I do like the fact that GM is getting better. The new Sonic (Chevy Aveo replacement) is expected to get 40 highway. That's right on par with the Focus and Fiesta and it's better than the Yaris. Chevy has improved a lot since 2004 (can't wait until the Cruze diesel comes out).

Beating the EPA highway rating (31 highway for an 04 Aveo auto) by 3 mpg is still a success. You're almost 10% over the highway with your combined tank. Considering you have an automatic transmission, I'd saying you're doing very well with your current setup.

Thanks Kodak, and thanks for the graph.

No problem. It gave me a chance to procrastinate without feeling terribly guilty.

I don't know if you can get terribly accurate numbers over such a short distance. (Your numbers do seem to be somewhat noisy.) Any chance you could repeat the experiment using a longer road?

Unfortunately, you are misinformed about your car's transmission. I also have an Aveo ('09) but it has the same automatic transaxle as yours.

The "hold" button does not work for the higher gears, or the way you think it would - it is only meant to keep the car in a lower gear when on ice or snow so you don't spin your wheels.

Again, your perceptions are not correct. I have done a lot of research on this and the problem is with the way the transmission is programmed. The tranny is a 4 speed and is electronically controlled, but unfortunately the shift points cannot be changed. However the biggest problem for fuel economy is the set point for it to go into torque converter lockup. On most cars this happens at around 40 MPH. On the Aveo (and some other Chevy models) this does not occur until 45 MPH - which is way too late if most your driving is being done at 40. When it does lockup it actually feels like a shift - you will see the RPM's drop and suddenly your MPG goes up dramatically.

Not exactly. The figure for highway MPG is correct and it is excellent at 37 MPG. But the figure for city MPG is inflated - it was probably 24 and the best you will get is 22 MPG, which really sucks. The very wide disparity between city and highway mileage is due to the late TC lockup. (AKA a "slushbox".)

Forget the aero mods. I tried, and it won't help. What we need is way of controlling the programming of the transmission to get it to do the TC lockup sooner.

Thymeclock, yeah you are right about not being able to upshift early with the hold button. I guess I just have to stick to footshifting my car.
What are you talking about? The EPA highway estimate for a 2004 Chevy Aveo sedan with automatic transmission gets only 31 highway, not 37 so it's not "excellent" highway mpg. The city estimate is 23 and I do agree that it might be inflated, but overall, compared to other cars sold in the same year the Aveo was not brilliant in city or highway fuel economy.

I don't understand. You have an automatic transmission, right? What do you mean by "footshifting"? :confused:

Despite all Aveos having the same engine and transmission, apparently there must have been some other tweaking done over the lifespan of the model and the way the gov't jiggers the numbers. My '09 actually does get 37 MPG with the A/C on at 65 MPH. That is better than other comparable cars of its model year, so it's hard to complain about that aspect. And that high EPA figure is how GM promoted the car to compete with other models such as the Yaris, the Fit and the Rio. But the city FE is worse than the EPA estimates. That's disappointing, particularly if you do mostly city driving, as we do. It wasn't until after I bought it that I could discover the reason why.

Thymeclock,

By "footshifting" I mean taking my foot off the gas a little and applying it back on to get my car to upshift. Normally when I accelerate, the car would just stay in the lower gear but when I do this I can get it to upshift, but it can only be done at speeds the car would normally shift at when I'm not accelerating. I just call it "footshifting" because I don't know what else to call it. I guess that does create some confusion so sorry for that.

Although I am a little disappointed in my car's EPA rated fuel economy, I do like the fact that the newer Aveos got better gas mileage. It shows improvement on GM's part. I would really love to get a new Sonic since they get great fuel economy (29/40).

It's usually referred to as "inducing a shift" and that is a useful strategy. With the Aveo we have found that often it is best to accelerate briskly to get into the higher gears as soon as possible. Accelerating slowly does not help at all, for the lower gears are really fuel consuming.

I thought that too before buying the '09 Aveo. However the city MPG estimate is totally unrealistic. Since GM is now Government Motors, the figures for the Sonic might also be inflated. Unfortunately there is no way of knowing for sure until you own one.

Thanks for the thread--it's reminded me again why I love my manual tranny!:D

In all seriousness, pretty neat experiment.

If your brave you can make a TCC lock switch :)
Don't forget aeromods if you spend any significant time on the highway, they will help alot, just not in the city...

I also drive an atx and feel your pain in city driving. However, I can usually get 30+ in city. Improving my driving techinque has helped a lot.

Der AUTO BILD Verbrauchs-Test - autobild.de

Watch the pictures there are many measured fuel consumtion curves. I was not able to find picture adresses?

From curves you can see that your aero effects most to the fuel consumtion and the engine is the second biggest factor at those speeds.

My lupo 3L consumes 3l/100km @ 100 km/h speed ;).

I was surprised at Hägar's fuel consumption when stabilized at Vmax (187 km/h GPS).
It was less than 10L/100km - though it obviously takes a far higher fuel consumption to get there.


Climbing inclines at 130 kph rather than "eco"-speed (95-105 kph) also reduces fuel consumption in my car - the deal-killer is the acceleration of course.
At Vmax, the fuel consumption to go up comparable inclines hardly increased and was lower than while climbing at 105 kph, which tripled and quadrupled consumption to well beyond 12 L/100km.

Weird things seem to happen @ speed ;)

Can't grab the picture's URLs either, but you can grab the pages where the graphs are:

Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de
Was kostet Vollgas? - Bilder - autobild.de

I get better instrumentation averages at higher speeds, but better tank to tank if the speed is kept low.

Maybe its something to do with the sample / calculation rate ?

It is very unfortunate that widespread, easy to access engine ECU/ECM programmers don't exist that are plug and play and cheap to own like the scanguage.

If I could easily change the shift points in my autotragic and change its timing a tad without massive effort I would probably still own the buick lesabre.

I think maybe some more effort for easy to use DIY solutions on this front need to be made, if the auto makers won't do it, you should have the ability to do it yourself.

Having to desolder and socket the eeprom in the ECU, get a burner and figure out the code yourself, really isn't plug and play or easy.

Anyone want to figure out the AVEOs eeprom for shift points to help this guy get the most out of his car ?

Interestingly I find something similar which I have always attributed to momentum keeping the vehicle moving and saving that fuel guzzling shift back one gear and unlocking the convertor.

At 95 kph I can drive to work on the freeway with no changes but at 85 kph the transmission shifts back , for the few hills there are , enough to move the revs up from around 1600 to about 2000.

This in turn is enough to move the fuel used up to around 8.0l / 100 (US 29 mpg) from the usual 7.3 (US 32 mpg) or so. A jump of about 10 % which is a reasonable amount.

Peter.

from the small amount of research I have done my sweet spot is 55 to 65, if I stick it in I can achieve 30 plus in my 1999 camry which is a feat in itself

My 010 cobalt gets the best FE between 25 & 45mph depending on conditions. P&G is different.

Comparison in the Prius - Mrs A and I had to travel down south recently and the start and end points were both at pretty much sea level - we used the same route on both occasions. On the way down I kept a high-ish average speed as we were in a hurry to do the trip in a day before some forecast gales struck the UK. Average (on the on-board computer) was only 42 MPG.

On the way back Mrs A took it easier, the average being 10 MPH lower (we filled up at both ends and reset the trip) - average was 49.

Actual speeds withheld to preserve licence point status ;)

...driver to officer: "...But, Officer, I wasn't speeding ALL the time..."

I know my maxima, when it was running good, got excellent fuel economy running nonstop at about 80. While it seems perverse, I think it hits a fuel economy sweet spot about 2500 rpms, so coupled with it being in the highest gear ratio, plus some cautious drafting, I managed to get 30 mpg on a tank.

Sadly though, I rarely can go that fast regularly, nor that nonstop.

I've improved the aero on my car a little (not enough, obviously), but the sweet spot for me should be 55-57 mph at this point. I rarely have a chance to cruise at that those speeds on level ground, since the freeway speeds here are typically 65-70 mph. What I have found is that the difference between 65 and 75 mph is ~ 4-5 mpg (17% difference).