Chevy Volt's 'Mountain Mode' is Vastly Underrated, Yields New Driving Strategies

By · May 13, 2011

Chevrolet Volt

The Chevy Volt has been out for a several months now, and it's been reviewed nearly to death—with the vast majority of those reviews being positive. We've even reviewed it in many different ways here on PluginCars.com.

Yes I've driven it quite a bit already myself, but recently I had the opportunity to use it as if it was my personal vehicle for an extended period of time. It was the first time I was able to drive it for more than a few hours or a couple hundred miles at a time. Over the course of five days I drove it on a daily basis to haul my family around, run errands, and even transport a couple of folding tables and six folding chairs back from one of those big box stores. I also took it on a 300+ mile road trip over the Cascade Mountains from where I live in central Washington to Seattle and back.

While the car was certainly everything many other reviewers have raved about (including myself)—quiet, fun to drive, and comfortable—the part of that time that I learned the most was when I drove over the mountains. For one, it was the only time I ever used gas the whole time I had the car. But more importantly, I discovered a very useful driving strategy for long hauls with the Volt that may have been covered elsewhere, but I haven't seen it and it seemed important to bring up.

Mountain Mode is a Great and Underrated Volt Feature

For those that don't know, the Volt has three driving modes to choose from: Normal, Sport, and Mountain. Normal and Sport are pretty self-explanatory, so likely the vast majority of people will just plop it into one of those modes and leave it there based on their driving preferences. But that mysterious Mountain Mode is probably being left alone more than it should. In fact, some very prominent Volt proponents have even gone so far as to say they hardly find a reason to use it at all.

But in my experience, Mountain Mode is extremely useful even for long drives without mountains.

At its root, Mountain Mode is meant to force the Volt to switch from 100% battery-powered mode to charge-sustaining mode (where the engine is burning gas to generate electricity, and sometimes even powering the wheels directly—basically acting as a hybrid) long before the battery is fully drained. GM engineers have said this is to preserve battery power to help get the car up steep slopes with an assist from the electric motors—hence the name "Mountain Mode." In contrast, in both Normal and Sport modes, the car will use up every last drop of stored battery power it can before switching to charge-sustaining mode.

So how is Mountain Mode useful for driving long distances even if there are no mountains? The Volt has a higher fuel economy when driving at highway speeds in charge-sustaining mode than when driving in the city in the same mode. The EPA officially gave the Volt a 35 city/40 highway mpg rating without using stored battery power, but in my experience that charge-sustaining fuel economy on the highway was closer to 43 mpg (yes, that's calculated without any grid-filled battery input). Given that when you get to your destination, there will likely be several miles of driving at city speeds, it makes sense to be able to do that in 100% electric mode if possible, instead of using fuel at the lower fuel economy. Unfortunately, if you drive in Normal mode, by the time you get to your destination you will have used all of those stored electrons to push the car along the highway at high speeds.

Unlike charge sustaining mode, the 100% battery-powered mode is much more efficient at lower speeds in the city. Using electrons to push the car along with all that wind resistance at higher speeds just doesn't make much sense. Some plug-in hybrids, such as the BYD F3DM, allow the driver to switch back and forth between all-electric and hybrid modes at will—and Volvo has made it a core feature of its upcoming V60 plug-in hybrid. Unfortunately, the Volt doesn't have a button that forces it to switch between battery-powered driving and charge-sustaining hybrid driving, but Mountain Mode can act as a proxy.

How does it Work?

First, estimate how much low speed driving you'll do at your destination—we're talking rough ball-park. Assume the Volt has about 30 miles of all-electric driving range at low speeds. Once you use up the battery charge to the point where you have only a few more miles left in the battery than you'll need to drive as an all-electric car at your destination, switch the Volt from Normal Mode to Mountain Mode. Within a few miles the car will switch over to charge sustaining mode, leaving your battery loaded with electrons. When you get to your destination, simply switch it back to Normal Mode and the car will return to all-electric driving.

When I left for Seattle on my long trip, I kept the car in electric mode until I used up about half of my battery—approximately 15 miles—which got me out of the city and about 10 miles down the highway. At that point I switched to Mountain Mode and within three miles my Volt test car switched over to charge-sustaining hybrid mode. I soon entered the mountains and the car did use some battery power to get me over both passes, but for the most part it was regenerating far more than it used on the way down the hill (another strategy here is to put the Volt in in "L" instead of "D," which provides a lot more aggressive regenerative braking). On the downhills I hardly used the car's physical brakes at all.

When I reached Seattle, I had actually regenerated enough energy to add about five more miles to my in-city driving range, for a total of 17 miles of all-electric city driving. It felt great to be driving in the city on electrons, saving fuel from being burned when it's least efficient and not emitting any pollution at ground level where it can do the most harm.

For me this was a chance discovery when I accidentally flipped it into Mountain Mode at the right time and realized very quickly how useful it could be. If I owned a Volt I'd be using this feature a lot more than it's typically given credit. Hopefully the strategy will help you out too. Give it a try and let me know what your results are—or perhaps you've been doing this all along?

Comments

· Wayne (not verified) · 3 years ago

Hi Nick:

Who was the individual that told you how to take advantage of Mountain mode?

Wayne Gerdes

· Adarondax (not verified) · 3 years ago

What we really need to know is did the Volt burn less gas making those 17 electric miles than it would have used to propel the car around Seattle.

· DeeCee (not verified) · 3 years ago

In response to how much gas it took to generate 17 mi of battery, Nick said he'd switched to Mountain Mode at about 15 miles remaining battery so actually gained 2+ miles in the L position going downhill (as I understand itl. I drive a Volt and have used this strategy myself as I have a steep grade to climb from town to home. If I use Normal Mode, the battery power very quickly is depleted.

· · 3 years ago

Wayne, As I said in the post, I discovered it by accident when I was playing with the buttons on the highway, but immediately grasped how it could be useful. Why do you ask?

Adarondax, I guess a need a little clarification from you on your question. It didn't burn any gas making those 17 electric miles. They existed because I charged it from the grid (and some of them were regenerated as I was going downhill using energy that would normally be wasted in braking). Emissions associated with the electricity used to charge the batteries vary widely by region, but are generally much less per mile than burning fuel. Cost per mile using electricity will also vary widely by region depending on how much you pay per kWh, but are also generally much less than the cost per mile of fuel even at 43 mpg (something like 2-3 times less expensive). Where I live, 96% of my energy comes from dams (no emissions) and it is the cheapest in the country at 3 cents per kWh, so it's always better to drive on electricity here.

· · 3 years ago

Dee Cee,

You're right, I did switch to Mountain Mode when I had about 15 miles of electric range left, but it didn't switch to Charge Sustaining mode until another 3 miles later (meaning it used another 3 miles of battery power). So add another 3 miles to your 2 and you've got the 5 I gained coming downhill and regenerating.

· · 3 years ago

In EU, Volt will have a switch to turn the EV mode on and off (atleast that was reported a while back). Not sure why they didn't give that here.

· Colin Summers (not verified) · 3 years ago

The reason for the switch in Europe and not in the USA was (at the factory) explained as a restriction from the EPA. They didn't want people to be able to just drive around in gas mode.

The Normal mode doesn't use all of the charge in the batteries, it just pretends to. The ICE by itself won't give you normal driving performance at freeway speeds without some battery boost, so the computer hides some battery from you. When you pass on the highway, even when the range on battery is zero, there is drive-power provided by the electric motor.

Someone needs to hack the Volt so interested drivers can see what is really going on and so that they can kick on the ICE when they want it.

· Adarondax (not verified) · 3 years ago

I believe Mountain Mode builds a charge in the battery by running the engine, sometimes at high revs. This is how it's described on page 9-27 of the Volt Owners Manual:

"Press the DRIVE MODE button to select Mountain Mode. If steep hill driving is expected, it is recommended to select Mountain Mode at least 20 minutes before driving on steep grades. This will allow the vehicle time to build a sufficient battery charge reserve. The engine may run when Mountain Mode is selected. If Mountain Mode is entered before four bars of battery charge, the engine will
run at a higher speed to build battery charge reserve. If Mountain Mode is entered above four bars of battery charge reserve, the
estimated electric range will adjust accordingly."

That means that Mountain Mode isn't just maintaining the battery's state-of-charge, it is burning more gasoline to add to the charge. That is the basis for my question.

· Charged Up (not verified) · 3 years ago

This is a good tip. I would concur with the Volt being more efficient at highway speed. I am seeing between 43 and 48 mpg at highway speeds of 45-60.

So the essential gist is, use the mountain mode at highway speed and save normal mode for city driving, if you know you don't have sufficient charge to go all electric.

· Chris C. (not verified) · 3 years ago

Hi, I'm one of the first Volt owners. Last year we immediately pounced on Mountain Mode as a useful tool for controlling the car's behavior, as you described. However I don't do it for the efficiency -- I do it because city driving is far more FUN in electric mode. So I put it into mountain mode in the middle of a long drive, and when I reach the end of the highway portion of the trip it still has some battery energy in it. Gas mode is less annoying when you're just cruising down the highway, so it makes more sense to run in that mode then. Of course the Ampera will have this explicit capability (protect charge for the end of the drive) so that you can enter a city's congested zone under electric power.

I find this most useful when I'm going to an event where I will be showing off the car. By using mountain mode I can arrive with some battery power and thus be able to demo the car in pure electric mode. Doing demos / test drives in gas mode is frankly no fun at all.

Thanks for devoting an article to this!

· Rooster (not verified) · 3 years ago

If you intend to use this technique again in the future, I recommend you put the Volt in Mountain Mode before you leave your home. You'll run on the battery until you reach the MM charge depletion point -- that will ensure you maximize your battery use. Otherwise, you could miss judge, and drain the battery below the MM charge depletion point if you change modes on the fly. When the engine turns on to run the generator, it will have to burn addition fuel to recharge the battery back up to the charge depletion point, and thus lower you MPG.

· · 3 years ago

@Colin "The reason for the switch in Europe and not in the USA was (at the factory) explained as a restriction from the EPA. They didn't want people to be able to just drive around in gas mode."

Hmmm ... EPA should revisit that.

· R.Patrick (not verified) · 3 years ago

Nice.
You've essentially used the Mountain Mode (and the mountains themselves), the L setting, and the electric/generator brakes to do an end-run around the restriction that the engine can't be used to charge the batteries.
Seems obvious, but only now, after you've pointed it out.
Again, Nice!

· · 3 years ago

So, the so-called Mountain Mode is essentially a forced series /serial hybrid mode? I think the reason it is better in this mode on the highway is that since it isn't actually charging the battery, the engine is running in an efficient range, and all the power is used to drive the wheels.

It's a strange thing that GM decided to do: they could have used the engine to charge the battery, and then shut it off until the charge is used, and then run the engine again -- this would let the engine run at it's best RPM all the time. But they did not do this -- the reason is they didn't want you to end the drive with much charge in the battery; so you would always then charge it with the plug.

The downside is that the engine RPM vary with the demand of the electric motor to move the car, and/or to move the car with the engine. Which kind of defeats the main advantage of a series /serial hybrid, I think.

The FVT eVaro is a "true" series / serial hybrid, and it is far more efficient than the Volt. It goes ~125 miles on 21kWh pack, then runs the 1100cc 20kW gen set for about 1 hour, which can charge the pack while driving at highway speeds, and then the gen set shuts off, and you drive for another 125 miles, then the gen set comes on for another hour or so. It only burns 2.2 US gallons and has a total range of ~425-500 miles.

Neil

· George Parrott (not verified) · 3 years ago

Great insight and suggestion. After 3800 miles with our Volt, I had not thought about this possible strategy.

Thanks,

George

· · 3 years ago

I hate to beat a dead horse and I know this is going to result in a string of replies but L gear in the Volt will not increase regenerative efficiency. When Nick states "I hardly used the car's physical brakes at all" he implies that stepping on the brake pedal applies the friction brakes. Like all major EV and HEV vehicles, the Volt is equipped with a Coordinated Regenerative Braking system which will always apply regenerative braking before friction brakes, even if the brake pedal is applied. Any strategy in putting the vehicle in "L" on the volt is purely driving comfort associated with more one pedal driving. Hopefully Brad's upcoming article on regenerative braking will clear this up once and for all.

· Jeff N (not verified) · 3 years ago

I mentioned using Mountain Mode like this about 3 months ago in a comment on Ron Gremban's article here on this site.
See: http://www.plugincars.com/my-bittersweet-chevy-volt-moment-106861.html

As for the FVT eVaro, the reason it gets such excellent efficiency is most likely due to it's low weight and extremely aerodynamic shape. It's not at all clear to me that the added efficiency of optimizing the generator engine RPMs can significantly overcome the added inefficiencies of electrical conversions and battery charge/discharge. Doing this will also age the battery faster. I personally suspect that the serial/parallel split eCVT strategy used in the Prius and Volt is the best overall choice when driving in hybrid "charge sustaining" mode at steady highway speeds.

If anyone knows of a good technical study of the generator->battery->motor versus eCVT efficiency tradeoffs please post the URL!

· · 3 years ago

Great article, Nick. I have been interested in Mountain Mode for some time.

@NeilBlanchard, The Volt engineers found that they got better highway mileage by switching the system to parallel hybrid mode, than continuing to use the serial hybrid mode, because the system would lose efficiency by converting mechanical energy into electricity, and then back to mechanical energy.

· · 3 years ago

regman, What I meant by using "physical" was the act of pushing on the pedals—as you allude to with your one pedal driving comment. It is true that most vehicles with a partial to full electric drivetrain use software to determine how much "electric" resistance and how much brake pad resistance to use when you press the brake pedal.

George, thanks for your comments—much appreciated. I'm feeling like wiping the slate clean of our previous encounters and starting over much more cordially. How about you?

Rooster, thanks for the suggestions... and you're absolutely right. Probably only makes sense to put it into Mountain Mode from the get go.

Jeff N, Sorry I'd missed that!

· Eric (not verified) · 3 years ago

I don't know if I agree that the results will be anything appreciable to use this strategy, if we assume goal is to reduce gasoline usage. To maximize gasoline savings, you want to use every last electron you can that came from the wall.

If you use mountain mode to preserve your charge until the city, 40% of your charge is preserved. Assuming, as your article did, a full range of 30 miles, that would leave roughly 12 additional all-electric miles in your car than you'd have if you ran in Normal mode.

Assuming 32MPG city, if you used those 12 miles on gas in the city instead of mountain mode, you would have burned 0.375 gallons of gas. If you use that on the highway instead (by use of mountain mode), that same 0.375 gallons gets you 16 miles... A savings of 4 miles.

So, if you arrive at your final destination with any more than 4 miles of battery range remaining, you really haven't "saved" any gasoline to speak of. The point here is that your estimate of when to switch back to Normal mode would have to be awfully precise, regardless of trip length.

In general I think the Volt is designed to maximize efficiency in its Normal mode, and the Mountain mode sacrifices efficiency for power when conditions necessitate.

I would still argue that driving a Volt in Normal mode except when needed for steep grades yields maximum efficiency.

· Eric (not verified) · 3 years ago

I guess I will add one more point to my previous comment, and that is that this strategy can yield a small amount of efficiency gain, but requires two caveats:

1) Mountain mode is engaged right from the start of the trip, so there's no chance of the motor trying to generate electricity to actively dump in the battery (less efficient).
2) Normal mode is engaged sufficiently in advance of the end of the trip so that all of the remaining EV range is used prior to the final destination... Even if this means the generator comes on again for a couple miles before the end of the trip.

Maximum efficiency savings of 0.375 gallons (not a whole lot, but in a normal 60 mile commute per day or something like that I suppose it can add up) is attained only when you arrive at your destination just as you run out of all electric range. Any generator running after, or any EV miles remaining upon arrival, cuts into that 0.375 gallons of saivngs. Having EV miles remaining at the end is probably the worst, as not using just a little EV range will quickly wipe out any gas savings you may have been able to attain.

· · 3 years ago

Nick, I understood that "What [you] meant by using "physical" was the act of pushing on the pedals", as I know that you are well aware of the previous regen controls discussions in plugincars.com. I was merely clarifying this point to other readers that may be new to this forum. I am somewhat a stickler for words in that "physical brakes" to me refers to the actual friction brakes (the disk/drum brakes) and not the brake pedal. Also, by including this "strategy" in your article, it implied to me ( and other potentially new/not verified comments by DeeCee and R.Patrick) that the use of L gear improves efficiency in mountains.

· · 3 years ago

Excellent story and great comments! This will all be of even greater utility as U.S. cities follow European leads in creating "no-internal-combustion zones" in downtown areas.

I will chime in with a story about the original reason to use Mountain Mode. On my family's sixth winter trip from Silicon Valley to Lake Tahoe since getting our Volt in December, I unaccountably forgot to engage MM before leaving. (Of course, on the basis of these exchanges, there's a slight benefit to driving a few local miles before flipping the switch as you get on the highway, but that's one more thing to remember as you start a long trip.)

About 10 miles before reaching Donner Pass, we paid the price: on the driver-side display, under the MPH number, we saw a small blue triangle with an exclamation point and a yellow message, "Propulsion Power is Reduced." I flipped to MM. As we continued to climb, our top speed drifted down to about 55 MPH. Then we reached a plateau area and were able to resume a higher speed while the engine worked to give the battery its MM margin. We then made it to the summit at 65+MPH. On this 225-mile journey that includes 8,000 feet of elevation, with three passengers and luggage, we averaged 35MPG, equivalent to the other trips (as described at http://www.calcars.org/calcars-news/1132.html ).

· · 3 years ago

Hi, everyone. I echo Felix' appreciation. I'll weigh in on a few points:

1. Regen braking is indeed applied first whether via L mode or via the brake pedal. Besides that, the Volt has a spectacular undocumented feature that all hybrids as well as EVs should have, but the upcoming Ford Focus EV is the first to actually announce: the ball that floats downward upon heavy braking is actually (verified through my Volt adviser) an indicator of how much friction braking is being applied. If you manage to keep the ball from moving, you are driving without friction braking and seriously maximizing your fuel economy, whether in EV or charge-sustaining mode. (By the way, I believe the upward float of that same ball is much less important, as EVs generally do not lose much efficiency during acceleration.)

2. I believe the reason the Volt has poorer charge-sustaining mileage than e.g. the Prius is not because of serial hybrid inefficiencies but because the Volt's engine has not yet been nearly as carefully tuned for economy. The Volt is, after all, a first-generation PHEV/EREV, while the Prius is now in its third generation (fourth, if you count the Japanese-only precursor to the '01). The Prius engine is an Atkins-Miller cycle (much lower pumping losses than the standard Otto cycle), has an offset crankshaft for reduced power stroke friction and a Dewar bottle to keep coolant hot for three days, and much more that GM hasn't yet had time to optimize. Such a difference in engine efficiency, as well as further-optimizable hybrid control algorithms, would be good reasons that the Volt's city mileage is lower than its highway mileage despite it being (among other things) a very strong hybrid. So, as good as the Volt is already, GM clearly has plenty of room for continued optimization.

Several years ago I did some calculations of possible serial vs. parallel hybrid efficiencies. My conclusion was that when all the loses and potentials for efficiency improvements are added up, the two architectures' efficiencies are similar enough that the winner can easily depend as much on each vehicle's quality of engineering as on the choice of architecture.

3. I believe GM decided to have the ICE's speed and output roughly follow the road load -- as with an ordinary hybrid -- for two reasons: First, it minimizes the average power and energy throughput that the battery is asked to deliver. With no Li-ion propulsion battery field experience to build on, this is one of many steps GM took to maximize battery life. As they get field experience, they will likely find they can work the battery of future models harder without significant warranty losses. Second, as with driving an ordinary hybrid, it is enjoyable to the driver to have the engine stop when the car stops, only starting again a while after getting launched, and satisfying to have the engine power low and relatively unintrusive except when lots of power is needed. In contrast, a constant-speed engine could be quite annoying.

4. Though not previously part of this conversation, Felix (in his LEAF as well as Volt) and I have both discovered since I wrote my "bittersweet" article (http://www.plugincars.com/my-bittersweet-chevy-volt-moment-106861.html) that low ambient temperatures and especially rain significantly negatively impact fuel economy of electrically-driven vehicles. I now regularly get 36+ miles per charge or around 40 mpg in both city and 70-mph highway driving. It seems these vehicles are far more sensitive to environmental conditions than is noticeable to gas vehicle drivers. (By the way, after another two months to the day, I had to visit a gas station a second time! It's getting to be a bad habit.)

· · 3 years ago

Ron and Felix,
Thanks for weighing in with your real-world experience in the Volt.

I've also seen that mechanically or electrically linking the ICE and the EV drivetrains should be about the same efficiency. Of course, in a company with a lot of excellent transmission designers such as GM (with little future in an electrified world), It is pretty likely we can guess why they chose a mechanical linkage.
I, personally, would prefer that GM provide the option of a constant speed engine by selecting some sort of "economy" mode. This would allow them to find out, in the real world, whether people would prefer a little harshness to more frequent stops to pay "The Man". By denying the option, clearly, we'll only find out what the NVH (Noise Vibration & Harshness) engineers who also have minimal career prospects in an electrified world.
Have you all noticed how the design decisions in the Volt seem to favor the workforce they have in place?

· · 3 years ago

Ditto that, Ron and Felix thanks for your thoughts and insight.

While much of the population, and indeed the media, still try to make sense of what the Volt/LEAF/Prius PHEV/i-MiEV/Focus Electric are (I'm still amazed that most of the people I talk with outside of our little circles have no inkling that there's a difference between a hybrid and electric car, let alone a PHEV... and let's not even get into series or parallel) it's exciting to see the whole automotive world shifting under our feet and to know that cars like the Volt are only the start. The Voltec drivetrain is a great opening bid, but it has a huge amount of room for improvement. Soon real competition will force these companies to innovate even faster.

· · 3 years ago

Ron,
Regarding the gauges, each manufacturer has played around with various ways of displaying efficiency. I personally do not like the bouncing ball on the Volt an my preference is the Escape HEV gauge. Unfortunately it is only available on the 2010 model year and later and only if you get the NAV screen. You can view a description on the Escape gauge by opening the second printing (page 75) of the NAV supplement at http://www.motorcraftservice.com/vdirs/SPubs/default.asp?TYPE=OWNERGUIDE....
Maybe Brad can include a description of all the braking gauges that each manufacturer is using as an addition to his upcoming Regen Brake article.

As far as the power sustained modes of the various vehicles, there are specific reasons why the Volt is less efficient. In general, series hybrid system will always be less efficient in this mode because the mechanical energy of the engine has to be converted to electricity and then back from electricity to mechanical. Each of the energy conversions is 5-15% inefficient, providing a round trip energy efficiency probably 75-90%. In addition, the most efficient engine operating point can not always be achieved because generator efficiency/speed/load curves do not line up with the engine efficiency/speed/load curves. Since the engine is directly driving the generator, you are always compromising the efficiency of one or both the engine or the generator. In contrast, the Toyota (and Ford) system can send the mechanical energy of the engine directly to the wheel (eliminating the energy conversion losses) while simultaneously using the generator to optimize the engine efficiency/speed/load point and absorbing (charge sustaining) any engine power not being directed to the wheel.

· · 3 years ago

Thank you for the great insight!

· · 3 years ago

@regman,
You said that: "the Toyota (and Ford) system can send the mechanical energy of the engine directly to the wheel (eliminating the energy conversion losses)"
The engine doesn't go directly to the wheel. It passes through a gearbox.
Gears aren't 100% efficient either. You can tell that if you've ever touched the transmission on a car that has been driving fast - you'll find it is pretty hot from wasted energy.
The Prius-style planetary gears are pretty efficient but still not perfect.
The same shunting of additional electricity to the battery can be accomplished by a traditional (electrical) series hybrid. Railroad trains have been doing it for over 75 years.

· · 3 years ago

Re. series/parallel efficiencies -- since you're talking specifics:

a) Yes, a series hybrid always has the dual conversion losses. However, Li-ion batteries are over 90% efficient except at very high rates, and motors and electronics are often operating in a 90-95% combined efficiency range nowadays; so the dual conversion losses are probably in the 30% range, approaching 20% in future vehicles. Of course, the Volt's partial direct drive bypass -- a synergistic byproduct of its re-purposed dual-hybrid transaxle -- reduces those losses at highway speeds.

b) It turns out that the Toyota/Ford power split transmission is not too efficient either, due to the power often being transferred between MG1 and MG2 for eCVT torque conversion. I have seen estimates of 30% losses during some phases of driving. The whole point of GM/BMW/Chrysler's dual-mode hybrid system -- using a second planetary gear system and some clutches -- is to reduce those losses.

c) There are inherent inefficiencies involved in designing an engine to work over a wide range of speed and torque, and (especially) to respond quickly to rapid changes in driver-requested power. Strong hybridization mitigates this some, thereby allowing for more efficient engine designs that are also operated in their most efficient regions more of the time. Toyota claims 38% peak efficiency for the Prius engine -- and average tank-to-wheels efficiency falls around 30%, with regen energy recovery accounting for some of that. In comparison, an ordinary engine's peak efficiency is more like 25-30%, with an average tank-to-wheels of more like 15%, even nowadays. In contrast, an engine built to a single high-efficiency operating point could reach 45% efficiency, both peak and average -- with a generator perfectly sized and tuned to it -- which could make a series hybrid efficiency-competitive despite its dual-conversion losses. Both the Volt's engine modus operandi and its clutch arrangement put the Volt's efficiency regime in the middle between that of a strong power split hybrid and that of a pure series hybrid. I believe it is less efficient (in each mode) than a Prius merely because of its infancy.

Note: In praising the Volt's indication of the onset and intensity of friction braking, I was not praising the ball display so much as the fact that that data -- critical for efficient driving -- is, for the first time I've seen, displayed for the driver in realtime. Now GM needs to TELL its customers that what they are seeing (when the ball goes downward) is the actual waste of energy.

· · 3 years ago

@Ron Gremban,
The electricity needn't go through the battery during Charge Sustaining cruise with the traditional series hybrid. This would be exactly like train engines do it today and is a lot more efficient than always going through the battery. Any excess power from the engine+generator can go into the battery. This means that the cruise losses can be less than 20%.

· · 3 years ago

ex-EV1 Driver, I never said there were not losses through the gearbox. I was merely pointing out the differences in the systems and why, in charge sustain mode, the Toyota/Ford system is more efficient. Gearbox losses will be similar in both but the Volt has the added losses of the double energy conversions.

Ron, I agree that the losses are in the 30% to 20% range which is similar to my statement that the efficiencies are in the 75-90%. And yes, at highway speeds, the Volt is not a pure series hybrid and can gain some of the efficiencies back.

My comparison and comments were specifically on charge sustain mode of the Toyota/Ford system vs. the Volt/series hybrid. As it turns out, there are no hybrid systems that are perfect. Most systems have operating scenarios that they shine in or that they are not ideal. For example, both of these systems lack in high speed torque capability, making these systems fall short in towing. The dual mode and crank-ISG type systems do not have towing issues but are more complicated (more moving parts that can break) are more expensive and have higher gear box/transmission losses. The Toyota/Ford systems are not as ideal for Plug-Ins because they require engine starting (to prevent generator overspeed) at relatively low speeds (compared to the Volt). Going into detail on what system is better in this or that driving scenario/mode is a much bigger topic but all have their advantages and disadvantages and each manufacturer must weigh these advantages and disadvantages for their specifica implementation.

As far as the Volt's ball, it may be the first that you have seen but I think the Ford Escape gauge is better gauge in that it not only gives you information on where you are braking but provides the threshold of where friction braking is applied, in real time.

Also, ex-EV1 driver is correct in that, by definition, charge sustain mode means that the energyis not going into the battery but rather from the engine, to the generator to the motor, to the wheels.

· · 3 years ago

@regman,
From my perspective, the Volt is the same as the Ford/Toyota with a few extra Rube-Goldbert 'enhancements' in the form of some brakes and clutches on some of the shafts feeding the planetary gear system.
It is not a traditional series-hybrid as was originally planned and announced.

· · 3 years ago

Ex-EV1 driver,
Although they have a lot of similarities (single planetary gear, engine, motor, generator), how they are all connected together result in significantly different operating characteristics. Think of it as carbon. Connect carbon together one way and you get graphite, another you get a diamond. You may think a diamond is superior but tell that to a Boy Sscout that is trying to improve the friction losses on the wheels on his pinewood derby car.

The Volt system has some advantages that the Toyota/Ford systems don't have but at a cost ($ and complexity). It also has a few disadvantages. But as I stated before, there is no perfect system for all vehicles and driving modes. If I had to summarize it, I would say the Volt wins as a Plug-In (especially at > city speeds), but looses once the engine has to come on either to sustain battery charge (lower efficiency) or to sustain power to the wheels (as evident in the need to have a mountain mode). The Volt also looses on complexity and cost.

· Dale R (not verified) · 3 years ago

I really appreciate this article. I am now getting 43.3 MPG in gas-only MPG in my Volt by using Mountain Mode and running the ICE on the freeway only, while saving the battery for the in-town portions of my long trips.

· GreenWin (not verified) · 3 years ago

Great article Nick, and excellent comments. Clearly the Volt is making a positive impression on these early adopters and reviewers. We like to read these comments as proof the volt concept works and works well. It is further testimony to the excellent engineering job done by GM's Volt technical team.

In my brief drive of the Chevy Volt I was astonished at how quiet and vibration-less is was in CS mode. While the ICE cycled on and off - I could only tell by watching the data display. The machine itself never gave me a clue as to when it was charging or depleting. Nice.

· · 3 years ago

@GreenWin,
You sound like a GM person or a shill for them with your parroting of the non-issue that they seem to focus a lot on. Are you?

· sue jones (not verified) · 3 years ago

I love my volt! 117mpg so far driving like a bat-out-of-hell if I'm going less than 40 miles that day.

One question i have is about whether it might be MORE EFFICIENT to drive in LOW GEAR! Normally one wouldn't expect that... but the Volt's "low gear" is actually a mode where electrical regen is increased, or so it seems. In fact, it feels almost as extreme regen as a Tesla (although nothing like the emergency stop you get out of max-regen braking on an AC Propulsion car.)

That is pretty cool because you can one-pedal drive most of the time, slowing down almost enough just by releasing the accelerator.

On the twisty mountain roads around here I can totally one-pedal drive in Low which is
very wonderfully relaxing! It always supplies the right amount of braking to keep the car from accelerating downhill.

I also believe that max regeneration is SAFER, because in an emergency or even normal driving, you start braking at least 1/4sec faster, at the point you release the accelerator and haven't yet reached the brake pedal.

So am I increasing my mileage by regenerating more? Decreasing it by driving more responsively (slowing down when I don't need to)? Or decreasing it by having Low implemented in some silly way I dare not contemplate, like using friction brakes or (gag) ICE engine braking? (I doubt it but crazier things have happened, and GM probably did not anticipate that I would chose to drive in Low most of the time!)

· Anonymous (not verified) · 3 years ago

The best way to explain the L mode is regen braking is moved from the brake pedal to the gas pedal. While in L, pressing the brake pedal uses the friction brakes only since max regen is already being used with your foot off of the gas pedal. I also only use L as there is then a clear delineation of what is regen and what is friction braking. In D I would have to look at the efficiency ball to notice when I have maxed out regen and it transitions to friction. As for the rear-end danger factor of using L, only night or bad weather would be an inappropriate time to use it since max regen is pretty powerful (more than downshifting in auto or manual cars) and not having brake lights come on could be a mistake. It would have been nice if the brake lights could come based on deacceleration rates and not brake pedal movement.

· Martin H. (not verified) · 2 years ago

Miles on gas reading is misleading for town driving as it includes distance when the gas generator is off (i.e. during regen. breaking and using the charge generated by the regen.). So in reality, you are getting even fewer miles on the gas in town than it says since it all falls under the "miles on gas". Wish any time the gas generator was off, the Volt would record that as electric miles.

I haven't figured out how much gas it takes to create a charge (in mountain mode) to use in town and compare that to the 37 mpg I got strictly on gas in town, but I don't suspect it will be any better. But again, the 37 mpg is inflated due to the distance travelled during regen. and the charge generated by the regen.

· · 7 weeks ago

Nick... THANK YOU for writing this post!!!

I left Las Vegas this morning to return home to the Los Angeles area. I've had my 2014 Volt since February, and my only other "long" road trip was to Del Mar. So before my trip to Las Vegas, I had averaged 172 mpg since I got my Volt!

I was at the Bellagio and there wasn't a charging unit on the property, so I started my drive home without a charge. On the first uphill mountain grade, "Propulsion Power is Reduced" showed up on my dashboard. So, I Googled to find out exactly what what meant... and I (luckily) found your article.

I changed the mode to Mountain as soon as I understood what you wrote. By the time I got to Hesperia, which is about 70 miles from home and where I got more gas, I had averaged a paltry 30.3 mpg in Normal mode. (I had driven between 60 and 75 mph.) 30.3 mpg??? I was pretty discouraged, and I was hoping things would change after the reset based on your new-found advice.

My results after driving the last stretch in Mountain Mode?

1) As I left the gas station, I had 15 mile range on my battery (when it had been exhausted four days ago when I arrived in Las Vegas).

2) I used 1.0 gallons for the 68 miles that I drove from Hesperia to my house, because I changed the mode to Normal when I was 15 miles from home. (Admittedly, Interstate 15 to the 210 freeway is almost all downhill, but I still had another 35-40 miles to drive on level highway roads.

What a huge difference. Any future long road trips I take, I'll be driving in Mountain mode. Around town, I'll keep it in Normal. I hope every Volt owner understands your advice. Thanks, again!

David aka Volted

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