Speed vs. Fuel Economy

[Aveomiler]

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.

[Sven7]

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.



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.

[JRMichler]

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.

[Kodak]

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

Edit: Let's see if this works:

[Rokeby]

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.

[Kodak]

Originally Posted by Rokeby

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.

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.

[JRMichler]

Originally Posted by Rokeby

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%.

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

[JRMichler]

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.

[Aveomiler]

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.

[Sven7]

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!