MPGe at Various Speeds

[honoreitiscom]

First let me thank gm-volt.com forum member "Fluke" who gave me his old "TED" device for measuring juice going to my 240 volt EVSE. He even paid for shipping. He had a new TED and no longer needed his old TED, which was perfectly good, and he offered it up on this forum. Thanks Fluke!

I promised Fluke I would use it to test MPGe at various speeds and publish the results here, so here you go:

MPGeSpeeds.jpg

Each data point was measured on the same 11.3-mile round trip, so elevation/terrain was not a factor. 1.6 miles of the round trip are on a side street max speed 35 MPH, the remaining 9.7 miles of each round trip were on a country road at the speed indicated in the chart. I used the TED to measure how many kWh it took to re-fill after each run.

The two main takeaways I see in this chart are:

1. Not a lot of difference between 25 and 40 MPH. If you have the choice of routes with speeds in that range, you might as well choose the route with a 40 MPH speed limit.

2. For anything over 55 MPH, the line drops steeply. And over 70 is horrible.

So to me there are sweet spots at 40 and 55 that give you the most bang for the buck, i.e. the most speed with least hit to MPGe.

The main variables and caveats:

• MPGe calculation assumes the EPA standard of 33.7 kWh per gallon of gas
• I was carrying the weight of 66 miles worth of gas in the tank on every trip
• Windows up, no climate control.
• No radio, headlights, or other accessories.
• Tires inflated to 50psi.
• No passengers, no cargo.
• Temps varied between 53 and 82 dregrees on the test runs, with most in the low 70s.

[DonC]

This is very cool. Many thanks for posting and taking the time to do the work.

However, it might be more useful if you didn't convert to MPGe and just left it in kWh/mile. I think people can relate better to kWh. MPGe is just such a weird measure.

[Steverino]

Nice! Thanks honoreitiscom! Question: are the speed points associated with the closest right hand tick line, or ? I am guessing each speed is actually tickless.

[barry252]

This is WAY COOL! Thanks for the posting. I remain humbled by your 72.9 mpc. I have crossed 50 mpc but haven't had the opportunity to repeat your tests just yet. But I see how it's possible! Maybe this weekend.....

Volt 63

[larry4pyro]

Great post honoreitiscom. This is very informative stuff. I wonder how much of the efficiency drop is due to aerodynamics load and how much is due to increased losses in the electric Voltec drive?

[2BeLivingGreen]

Honoreitiscom,

Great work and a very useable plot too. Thanks for the hard work and documentation. This answered alot of questions I am sure as to how energy vs. speed in the VOLT works. Just one more example of great knowledge sharing on this forum.

[mrosack]

That's awesome, thanks! Makes me wonder how the EPA MPGe estimates are calculated, though - based on that graph I have no idea how they came up with 95 MPGe city...

[DonC]

Makes me wonder how the EPA MPGe estimates are calculated, though - based on that graph I have no idea how they came up with 95 MPGe city...

They put the car on a dynamometer and run it through the drive cycle until the car can't complete the cycle. Then they charge the battery and measure how much juice it takes. Then they multiply the number of miles the car went by .7 to account for real world conditions. Then they calculate how miles it takes to go 100 miles. Then they calculate how many miles you could go using 33.7 kWh. That's the MPGe number.

For example, the Volt can go 100 miles (actually 143 before adjustment) on 36 kWh from the wall, which gives 93 MPGe (33.7 kWh / 36 kWh * 100 miles), meaning the Volt will go and adjusted 93 miles using 33.7 kWh from the wall.

[2BeLivingGreen]

Looking at your MPGe curve, do you think that maybe your VOLT went from Single Motor Extended-Range Driving to Two Motor Extended-Range Combined Driving at about the 49-50 mph knee in the curve? Maybe the VOLT powertrain saw the efficiency dropping and released the ring gear to pick up efficiency?

[pavers123]

I have an electric bike, and I struggle to get it over 40mph. At anything over 40mph cutting through the air feels like trying to sprint in a pool full of water.

I've also noticed that on the highway in the Volt over 70, there's massive increase in the rate at which estimated miles depletes itself.

This is all part of the reason I'd like to have a kwh remaining gauge in the Volt, and not just have the Volt tell us how many "miles" remain. I'd like to actually watch the kwh in battery storage going down. I think the typical Volt owner (except for possibly those similar to Senator Levin) is savvy enough to figure out how to interpret a "kwh remaining" indicator.

All of this, makes me appreciate the gas wasted when driving a "normal" car at "normal" highway speeds vs the legal 55-60 mph range.