* Slow Down * ? !

[MrFixit]

Don't like your EV range? -- Slow Down !

Please spare me the criticism...
I do know that you really can't do this under most circumstances because you will be run over !

There are a lot of factors that can effect EV range performance, and there are many discussions in this forum related to this. One thing that may be underappreciated is speed. There is a tremendous difference in EV range when mostly driving under city conditions vs. 75 mph on the highway.

Performance on a flat highway is limited by 2 primary factors (rolling resistance of the tires, and Air Drag). There are a couple of fairly simple equations that can be used to estimate the power needed (and hence the EV range) as a function of speed. Some of the parameters I used are estimates, but here is a curve that shows how significantly speed affects EV range:


If you are a glutton for punishment, I have attached a screenshot of the basic spreadsheet that shows all the assumptions / parameters that I used to make this curve. It shows a Reddit link where I found a nice discussion surrounding this topic.

You can hardly see it, but this is a thumbnail link below...

 

[Robert_Alabama]

I agree with the curve. That’s pretty much my experience. I use the following to determine whether I can slow down below speed limit.
1) Safety (if traffic is heavy or even moderately heavy, I’ll drive with traffic, even if that means above speed limit). Usually traffic here is heavy on interstate highways unless it’s late at night or maybe middle of week.
2) How much time I have for the trip (am I pushed for time?) If I have time, I’ve occasionally taken backroads instead of interstate hwy if distance travelled is essentially the same.
It’s generally just too dangerous to drive under the speed limit on interstate highways most of the time here.

 

[AHolbro1]

Aerodynamic drag increases with the square of the speed......but I leave it to the BEVins to worry about such. I bought the Clarity as it was the only reasonably affordable car that would come close to paying for itself in fuel savings given my 102 mile round trip commute and plan to work another 2 or 3 years prior to retirement. Std hybrid wouldn't fit the bill, although the Honda Insight comes close. I use HV mode to ensure I have EV range for the city and likely stop-n-go portion of the drive, but if it needs to burn petrol to deliver the same performance as a regular car, then petrol it is. The 7 gal fuel capacity was my biggest worry, that I'd have to top-up more often than every 4th day with the J'aag, but find I can stretch it to 4 days easily enough.

Of my 51 miles in the morning, 46 are highway with posted limits of 70 and 75 mph. On the return, I have the 5 miles of city driving, but then 20-25 miles of highway are prone to be stop and go or average less than 30 mph. If I use the car strictly for commuting and don't make any weekend EV only trips to town and back, I average about 65 mpg...or did until winter set in. I leave climate control off until the ICE is on in the mornings. Even with "winter" (as I call anything below 50 deg F) by the afternoon trip home I usually need ac which doesn't seem to affect EV range as deleteriously as heating. Even so, round trip petrol consumption is trending more toward 2 gal/day vs. the 1.6 it had been averaging over the summer and early fall.

 

[insightman]

After driving Honda CRX Si cars for many years I saw the Honda VV prototype for the yet-to-be-named Honda Insight at the 1999 auto show in Detroit. The idea of an electrified CRX that could get 70 MPG intrigued me so I drove the 44 miles back to Detroit the next day to look at the car again. Knowing that I would have to slow down to maximize my gas mileage, on my return trip I abandoned my normal 70-80 mph speed and drove 55 mph to see what it was like.

It was really hard, but I decided I could do it and when I returned home I placed an order for whatever the car would be named. It arrived a year later. Honda honored my patience and enthusiasm by putting my Insight (#221) in an enclosed, single-car carrying truck and driving it from Torrance, CA, to Ann Arbor, MI. It was the first Insight in the midwest.

I found life in the slow lane to be a completely different world. On the expressway, other drivers would ride my rear bumper, trying to urge me to go faster. I learned to seek out a semi truck to follow. Then people couldn't expect me to go any faster and I got the extra MPGs through drafting. However, after replacing a windshield, I learned not to follow too close.

When I saw another car going slower than the semi I was following, I would slow down and follow that car at a respectable distance. My motto was "Nobody can out-slow me!" My poor wife, who formerly criticized my speedy driving, would go crazy with my slow speeds. She also didn't like that I would turn on the AC only once a year--when we were dressed up to go out for our July wedding-anniversary dinner.

I didn't have too much trouble getting 85 mpg on a tankful of gas in the summer. The MPG gauge ruled my life. When we got our Clarity in December, 2017, I used my well-practiced hypermiling techniques but could never break 50 MPG in HV. I was disappointed I couldn't do much better than the rated 42 MPG. I decided the Clarity, which weighs more than twice as much as my Insights (I bought a 2nd one in 2006--the last one I could get), was just not as amenable to hypermiling techniques and 42-50 MPG is amazing for a big, luxurious, 2-ton car.

So on the rare occassions when I drive our Clarity, I keep the speed down, but don't expect spectacular results. In 5 years we have just 15K miles on our Clarity because our 2021 electric MINI Cooper is so much fun to drive for local errands that my wife and I drive that car almost exclusively. In a little more than 2 years, it already has 13K miles on the odo. It's so much fun that I've regressed to my old pedal-to-the-metal CRX Si driving style. However, the MINI has no clutch which resulted in an unanticipated consequence: My 2-pedal wife bumped me to the passenger seat now that she is finally able to drive the fun car in the family.

So I agree with the @MrFixit's message: going slower is definitely more efficient. However, there are psychological limits. In 2006 a group of drivers stretched a Honda Insight's 10.6-gallon gas tank to go 2,254.4 miles (as far as Ann Arbor is from Los Angeles). Even at my hypermiling prime I couldn't comprehend enduring the boredom of driving hour-after-hour at 18 mph like they did to get a big number like that.

 

[AHolbro1]

When I referred to the Insight, above, I meant the current generation. Props to you, Insightman.....but with those winning Reliant Robin looks.....that's a hard "NO!" I just couldn't....even if it would do naught to 60 in 3.5 and got 99 mpg! And yes, with the fender skirts, the Clarity channels those early Insight aesthetics just a bit....but the interior wasn't an overwhelmingly large step down from the rich burled elm and Connoly leathers of my Jaguars; particularly as the company's decision that despite increased productivity realized during WFH era it's better if we all drag-a$$ back to the office coupled with FJB's economy dictated a cost cutting measure.

You should dump the hypermiling crap and flog the Clarity like you do the Mini. They are not unfun to drive. Admittedly, not the same enjoyment as watching that majestic leaper, perched on the leading edge of a long, sexy bonnet pointing the way, and listening to the sweet music of a 4 liter straight six AJ16, not to mention the difference reflected on the faces of external observers....but hey! Treat it like a normal car and it acquits itself quite well. Now, that comes with certain underperformances with respect to certain of its capabilities, like fuel efficiency, for instance. But the hybrid powertrain is an entire system designed to move the car. This one has the unique capability allowing you utilize only a portion of the system to avoid using petrol if that is your bent, but in doing so, one deprives oneself of the full capabilities the car offers.

As to Insightman and BobBama's slow-poking, to each their own and I don't criticize, but it's not for me and I respectfully ask that you and your ilk keep to the rightmost lane while in the great state of Texas! Actually, as many newcomers soon learn, it is not at all uncommon that a Texan will slide over to the shoulder when you run up behind them....not even tailgating as such, but many recognize the closure rate and slide over to let the faster car by. In the spirit of Chevy Chase and Bill Murray in Caddyshack, "We have a right lane AND a shoulder, the shoulder would be good for y'all!" ;-)

 

[MrFixit]

Actually, as many newcomers soon learn, it is not at all uncommon that a Texan will slide over to the shoulder when you run up behind them....

In Maryland it just became a law that if you are in the right lane and approaching someone on the shoulder, you are required to move left if possible. This is obviously geared to protect disabled motorists / emergency vehicles, but I could picture Insightman slow-poking on the shoulder and causing a calamity as everyone else tries to skip over to the left lane and zip around.

 

[insightman]

In Maryland it just became a law that if you are in the right lane and approaching someone on the shoulder, you are required to move left if possible. This is obviously geared to protect disabled motorists / emergency vehicles, but I could picture Insightman slow-poking on the shoulder and causing a calamity as everyone else tries to skip over to the left lane and zip around.

I always kept to the posted speed-limit--or to the minimum speed limit--except when I could find a slower vehicle to follow. I wasn't having any fun, however. @AHolbro1 knows how to have fun--even in a Clarity.

 

[Jim Matthews]

To get the best range (per tank) use local roads and concentrate on using the optimal "demand" that shuts of the gas motor.

Coasting, timing lights and smooth turns that avoid coming to a complete stop will also help.

On the highway, the obvious admonitions apply - carry only what you need and properly inflate your tires.

 

[Dan Albrich]

Perhaps like others, when I got the Clarity (sort of my first fuel efficient vehicle), I got kinda focused on energy consumption. I wanted to do all electric all the time and tried to maximize EV miles. We did things like dess like eskimo and keep the heat off, drive slow, use only heated seats if we used heat at all, and used other advice for saving power from this forum. I later decided to just get in the car and drive it like a normal car. I use the heat when needed etc. And yep, sometimes burn gas because the EV-only range doesn't cut it depending on my trip length/s. But I do feel good about burning substantially less gas than I used to. I especially appreciate it when gas prices have been so high.

As for speed, I'm really not a fast driver, and haven't been since I was 16-18 years old. That's never changed.
I would say though for folks who do speed up to a stop if you know what I mean, Clarity at least reclaims some of that energy especially if you use the paddles or max regen in sport mode.

I realize many cars do have adaptive cruise control. To me this is simply a killer feature for driving in traffic. I select sport mode, max regen, and 1 car length and let my car (not my foot) manage stop-and-go traffic. Wow, what a life (and back) saver.

I would add, even now that I've gotten lazy about energy use with the car, the energy saving tips I learned have stayed with me. i.e. I now know how much energy cabin heat requires, and at least turn off when not needed. etc.

 

[Tek_Freek]

I agree with the curve. That’s pretty much my experience. I use the following to determine whether I can slow down below speed limit.
1) Safety (if traffic is heavy or even moderately heavy, I’ll drive with traffic, even if that means above speed limit). Usually traffic here is heavy on interstate highways unless it’s late at night or maybe middle of week.
2) How much time I have for the trip (am I pushed for time?) If I have time, I’ve occasionally taken backroads instead of interstate hwy if distance travelled is essentially the same.
It’s generally just too dangerous to drive under the speed limit on interstate highways most of the time here.

I could have written this.

I guess I'm different. I don't baby the accelerator to get maximum mileage. I just drive the car. We took back roads from Williamsburg, VA to Raleigh-Durham for a flight to Las Vegas (non-stop) and it was a really pleasant drive. The time difference was about 20 minutes. Good trade off.

 

[MrFixit]

Many times the back road routes take a little longer, but are actually fewer miles.
A perfect trade for EV operation (slower speed, and less miles) if you have a little extra time.

 

[David Towle]

Don't like your EV range? -- Slow Down !
here is a curve that shows how significantly speed affects EV range:
/QUOTE]
Excellent curve your numbers on the graph line right up with mine. But the question I have never seen well answered is why EV mileage goes down with speed so much more than ICE vehicles? My guess is the ICE efficiency must be going up as the power needed goes up but its just a guess. My old BMW would vary just a couple mpg between 60 and 80 mph.

 

[MrFixit]

I think the difference lies in the inherent inefficiencies of the ICE. With the EV, the loss between the HV battery and the wheels is quite low. This means that the consumed energy goes up directly with the drag and rolling resistance. The ICE itself has a substantial loss, which is largely dominant so the drag and rolling resistance has far less of an impact in the total energy equation.

I think ICE vehicles have an efficiency of something like 40%, so there is a 60% loss in heat and friction. This dwarfs (or greatly reduces) the effects of drag and rolling resistance.