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 Post subject: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Wed Aug 31, 2016 1:27 pm 
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Joined: Fri Jan 22, 2016 11:45 am
Posts: 72
Location: San Francisco, CA
I know that energy efficiency relies on a lot of factors: terrain, temperature, wind, number of passengers, etc.

Given whatever assumptions you'd like to make for a real-world driving scenario (i.e. flat road, no wind, 72 degrees Farenheit, one adult driver, etc.) what do you think is the maximum expected mi/kWh for a 2016 SE and what MPH do you have to drive to achieve it?

Basically I'm wondering what scenario the VW engineers designed the car for optimal efficiency.

After 7 months with the car I'm averaging about 4.4 mi/kWh driving 18mph in hilly San Francisco.

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Thu Sep 01, 2016 10:14 am 
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In my own personal experience, with all peripherals and creature comforts shut off, except radio, during the daytime... doing 55 mph, sometimes a bit less, hardly ever touching the brakes, and driving smooth, in "D", paying attention to changes in elevation and coasting down hill when you can... my best has been 6.1 to 6.3 miles per kwh, starting and ending at the same location and elevation for the drive.

It can be done, but you need freeway or interstate on polished concrete, Bridgestone Ecopia 422 Plus tires set at 45 psi, and very, very smooth and steady driving techniques, with traffic that is accomodating on freeways or interstate. I try to get way far back behind a big truck, so cars that come up behind me know I am not the one impeding traffic, I can't drive faster than the truck in front of me, so they go around me.

You might have some luck heading south on 101 or interstate 80 to Sacramento and back, but not in town, in San Francisco. Way, way too many herd mentality drivers there with poor driving habits, driving combative instead of smooth. Just too many people there.

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Sun Sep 04, 2016 5:45 pm 
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Joined: Mon Nov 02, 2015 2:32 pm
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Location: Santa Cruz, CA
It's a tough question to answer because there are so many variables like you mention, but one thing I've learned is that smooth coasting with no turns at low speeds is really your best friend if you're looking at opimal efficiency.

I took a scenic drive down to Monterey this morning across varied terrain, temp was in the mid 60s, little wind or humidity, and I had radio and vents on but no A/C. The best stretch was definitely along the beach, eco+ mode, foot barely pressing on the pedal, coasting at 30 mph. I was seeing 8-10 mi/kWh here and it never dropped below 7. Another very good stretch was going from the beach to the highway, 45 mph, getting 6-7 mi/kWh.

It's really all about getting momentum and keeping it going. Starts/stops will drag your numbers down and going uphill will completely kill them.

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Mon Sep 05, 2016 2:16 am 
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Joined: Sat Jul 25, 2015 2:24 am
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Location: SoCal
cctop wrote:
After 7 months with the car I'm averaging about 4.4 mi/kWh driving 18mph in hilly San Francisco.


I would say you're doing very well, considering not just terrain but also constant stop and go.

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Tue Sep 06, 2016 7:28 pm 
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I've had mine since January (2016 SE) and I average 5.2 mi/kWh. Washington DC is not as hilly as San Fran, which probably makes a difference. And although there's often plenty of stop-and-go rush hour traffic here, I live downtown and work just outside the city, so I usually avoid too much stop and go. I almost never drive above 60 mph, since I don't have a far commute, and most places I go you can't get going that fast even if you wanted to... that is DC for you. Going uphill really is noticeable when it comes to consumption, so you're probably doing quite well for SF.


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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Wed Sep 07, 2016 12:27 pm 
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~18 mph for 8 mi/kWh
(steady state on flat, smooth tarmac with no wind at 72f with no A/C or other accessories) :geek:

source

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Thu Sep 08, 2016 3:06 pm 
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Joined: Fri Jan 22, 2016 11:45 am
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Location: San Francisco, CA
Thanks Verkehr! That's great data.

Are the numbers you quoted listed on this sheet? The closest thing I see is on p.2 in the box "Fuel Economy at Steady State Speed, 0% Grade" where it says 126.5 Wh/mi (7.9 mi/kWh) at 20mph.

I plotted the points on a chart:

http://imgur.com/GlvFfpM

It confirms the general knowledge that driving 80mph is about 50% less efficient than 60mph.

But I'm surprised how low the most efficient speed is, and also that efficiency decreases so linearly as speed increases.

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Thu Sep 08, 2016 3:45 pm 
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We've averaged 4.9mi/kwh, 29mph here in the White Mts of NH over 2.5K miles. We always drive in the B mode little traffic :D . 2015 SEL


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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Thu Sep 08, 2016 5:17 pm 
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Joined: Sat Dec 19, 2015 4:16 pm
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cctop wrote:
Thanks Verkehr! That's great data.

Are the numbers you quoted listed on this sheet? The closest thing I see is on p.2 in the box "Fuel Economy at Steady State Speed, 0% Grade" where it says 126.5 Wh/mi (7.9 mi/kWh) at 20mph.

I plotted the points on a chart:

http://imgur.com/GlvFfpM

It confirms the general knowledge that driving 80mph is about 50% less efficient than 60mph.

But I'm surprised how low the most efficient speed is, and also that efficiency decreases so linearly as speed increases.

Admittedly I make some assumptions with the most efficient speed, so bear with me as I explain my thought process - some German e-Golf (here at 5m28s), not sure if this is pre-production or otherwise, lists instantaneous consumption in kW. This car shows 0.3 kW load at rest in "ready" mode which helps explain worse efficiency at 10 mph than 20 mph despite guaranteed less aerodynamic drag. Noting similarities to the Nissan L3af motor, there should also be a few percent lower combined motor+inverter efficiency at low speed for the geared up single speed motor (see pg. 12), but as a percentage of 1.37 kW at 10 mph that is dwarfed by an assumed ~300w ancillary load. I plotted the same data as you but with kW and kW offset by 0.3 to factor out ancillary devices, and found consumption still more than doubled between 10 mph and 20 mph. So I believe there's some efficiency left below 20 mph and based on my experience found that to be 18-19 mph.

Note: the intercepts here are arbitrary but the scale helps show the Wh/mi inflection
Image

PS: check out that government site's BMW i3 data for a really efficient crawler. 8.64 mi/kWh at 10 mph

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 Post subject: Re: What's the best expected mi/kWh and speed to achieve it?
PostPosted: Thu Sep 08, 2016 6:29 pm 
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Rsolaregolf wrote:
We've averaged 4.9mi/kwh, 29mph here in the White Mts of NH over 2.5K miles. We always drive in the B mode little traffic :D . 2015 SEL


Try only shifting into "B" mode when you need to brake, instead of all the time. You'll be surprised at the increase in miles per Kwh. Think of it like taking your TDI and shifting the stick shift from 3rd to 2nd gear to engine brake. With practice, you can judge speed and distance and hardly have to step on the brake pedal at all, using the "B" mode only. You can coast a lot farther in "D" mode and then only use "B" mode when necessary. Much easier on the car. More range per recharge. It takes a little bit of practice, but I find it worth it. Car still feels like a stick when done so.

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