Last week we heard from i3 REx owner John Higham in a post he wrote which detailed his thoughts on the i3’s range extender restrictions for the North American market. John certainly didn’t mince words and offered his reasoning why he believes the range extender on the i3 should have its artificial restrictions (which are in place to satisfy CARB), relaxed a bit. John also promised to do a road trip which would take him from the San Francisco Bay area up to the 7,228ft Donner Summit in Lake Tahoe and report on the range extender’s performance under these strenuous conditions. Below are his findings.

SF Bay to Tahoe by the Numbers, Part 2

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Nailed it.  Well, nearly.

In Part 1 of this post about all things REx, I declared that a US spec BMW i3 REx could not make the popular weekend getaway of Lake Tahoe from the San Francisco Bay area without being speed limited within 15 miles of Sacramento. How speed limited depended on the slope of the road as you climbed east into the mountains, but top speed would range from 40 to 55 MPH. The alternative was to fully charge in Sacramento before any significant climbing begins and then again in Colfax about halfway up the hill. This makes such a drive impractical.

I also declared that a European spec’d i3 would make it no problem, so long as one kept the diminutive 1.9 gallon tank filled and the feature known as “Hold Mode” engaged. In fact, European cars have made similar drives into the Alps.

The basis of these declarations is simple physics. In Part 2 we test the physics from Part 1.Twice. First with a U.S. spec BMW i3 REx and then with a European spec i3 REx.

OK, I lied. I don’t have a European spec i3. But I do have a US spec i3 that has been modified to behave like its schnitzel eating cousin.

A Quick Summary of Part 1
The California Air Resources Board (CARB) developed a class of car called the Battery extended range Electric Vehicle (BEVx). Some say the BEVx was never intended to be a car with mass appeal that can be driven like any ICE-mobile.  But I ask, why not? Actually, what I usually say is “Why the hell not!” while shouting and pounding the table with my fist. I digress.
I believe that the BEVx class of cars represents the bridge from plain ol’ Internal Combustion Engine (ICE) cars to pure electric that will finally allow the public to embrace EVs without looking back. Except.

There is one teensy exception and it is what engineers call a “corner case.” In this situation the “corner case” refers to those people who require a car to maintain freeway speeds over sustained elevation gains. That’s what this post is all about — to test how big that corner case actually is.

California’s San Francisco Bay Area lies at sea level and the drive east to Lake Tahoe follows the Sacramento river, never gaining significant altitude for about 50 to 100 miles, depending on one’s starting location. Continuing east past the capital of Sacramento begins what is at first a gentle climb into Gold Country. Assuming the route is along I-80, the slope increases significantly past Gold Country until Donner Summit (elevation 7,228 feet) is reached 95 miles east of Sacramento.

The i3’s APU is sized such that it can maintain freeway speeds, but not to maintain freeway speeds and simultaneously gain significant altitude.  It’s simply not possible to drive from the SF Bay Area to Tahoe in a reasonable amount of time with the US spec’d i3. Of course if you have the patience to charge every 60 to 80 miles, you can drive your i3 from the Bay Area to Tahoe or anywhere else for that matter. But that is impractical, even with with so-called fast chargers.

Since this post comes in two parts, and the test drive to Tahoe also comes in two parts, potential for confusion exists when referring to them.  Let’s dispatch any confusion and call the first test The Apple Pie Test and the second test The Lederhosen Test.

The purpose of these tests isn’t to prove you can drive an i3 to Tahoe by taking logical opportunities to charge. You can. It’s been done. The purpose is to prove the assertions made in Part 1. First, that the US spec’d i3 REx is hobbled as compared to its European counterpart and second (and more importantly) that an i3 REx is more than a great EV; it has potential to be the only car you need.

Oh yeah. No math in this post. I promise.

The Apple Pie Test

The Apple Pie Test is simple: try to “REx it” to Tahoe and see how far you get. (Oh, I’ve made REx a verb, but the Oxford dictionary hasn’t caught up yet.) Since this is my test, I get to make up the rules. The rule is simply to take a BMW i3 as CARB intended it to be delivered to the public and drive it along I-80 until the car becomes speed limited, then compare the observed results with the predicted results from Part 1.

To do this test I left the Benicia, California, CCS fast-charger with 90% SOC and a predicted range of 60 miles.  The drive toward the Tahoe region is essentially flat for about 63 miles along I-80, then the road climbs into the Sierra Nevada mountains. I planned this section of the drive to be all electric until such time I hit the foothills. The goal was to set the cruise control to the posted speed limit (65 MPH) and simply keep driving powered by the REx until the car became speed limited.

In Part 1 I calculated that the car would become speed limited at about 725 feet elevation gain and by using the elevation profile in Google Earth, I estimated that would occur about 12 miles east of Sacramento.

The actual drive didn’t work out exactly like that, but close enough for the rough assumptions that were made. At first the speed limitation was subtle. I started to suspect the car was speed limited at around 800 feet elevation (750 gained), “flooring it” to coerce an increase from 65 MPH with the cruise control set, I achieved about 67 or 68 but no more. But by 950 feet elevation gain the effect was no longer subtle. Not only could I no longer keep pace with traffic, but was feeling very vulnerable and was searching for an exit in earnest. On some of the steeper portions of that section I was under 55 MPH indicated with traffic whizzing past at 70 MPH and above.

Anyone who has owned a BMW for very long can tell you that the speedometers are optimistic by at least 5%, if not 7%. So, that 58 MPH in the photo is closer to an actual speed of 55 MPH.  In Part 1 of this post I made a table of predicted top speed as a function of the grade of the road. Using the GPS coordinates of the road and Google Earth, I found the grade of the road at the precise point is 3%; the table from Part 1 predicts a top speed of 60 MPH on a 3% grade; close, but some refinement of that table is in order.

In summary, the Apple Pie Test demonstrated that all that analysis, the calculations, graphs and so forth from Part 1 were within the margin of error that could be expected for the rough assumptions that were made.

More importantly, It proves that you can’t just REx it to Lake Tahoe in an i3. Luckily, there is a CCS charger in Sacramento, so moments after the above photos were taken I turned around and headed straight for it. With the miracle of regeneration the i3 got its SOC back up to a respectable level and I REx’d it all the way back to that CCS charger with no issues.

Hold Mode and Coding

The Lederhosen Test requires the use of a feature known as “Hold Mode”, which is on all Euro-spec i3 equipped with the REx; perhaps even all such cars destined for anywhere in the world outside of North America. What Hold Mode does is engage the REx (or more specifically in CARB-speak the APU) to maintain the battery State of Charge (SOC). Sounds a bit boring and perhaps it is.

The fact of the matter is, US spec’d cars have Hold Mode; the car’s onboard intelligence switches it on automatically when the battery SOC reaches 6.5%. The European version of the car also will switch on Hold Mode automatically when the battery SOC reaches 6.5%, but the European version also allows the driver to manually engage Hold Mode whenever the battery SOC is 75% or less.

The difference in the US spec’d car and its European counterpart is perhaps subtle, but as we shall see, the difference means everything if you require a car to maintain freeways speeds and gain significant elevation simultaneously.

What is important here is to understand that the US-spec cars do in fact have the European-spec Hold Mode programmed into the car.  The menu option that allows the driver to engage Hold Mode manually is simply hidden from the i3’s iDrive menu. For someone skilled in the seedy underbelly of the BMW tuner world known as “coding,” enabling this hidden feature in the iDrive menu is trivial.  To be clear, this practice is most likely frowned upon by both BMW NA and CARB.

To satisfy scientific curiosity, I “coded” my i3 to enable Hold Mode, Euro-style. On to the Lederhosen Test!    (click through this link to read about how to code your i3: Code your i3)

The Lederhosen Test

As noted in the last paragraph of the Apple Pie Test, as soon as I became speed-limited near Auburn, I turned around and returned to Sacramento and specifically to the CCS fast charger there. After plugging in and after i3’s SOC had reached 90%, I once again set out along the same route toward my final destination in Truckee, California, near Lake Tahoe. Hold Mode is only available if the SOC is 75% or less, so after leaving the CCS charger I drove the first 12 or 13 miles all electric.

The only difference in the two drives was the SOC at the bottom of the hill and manually engaging Hold Mode. This simply means the REx was used in the Apple Pie Test to “hold” a 6.5% SOC but on the Lederhosen Test, it was used to “hold” a 75% SOC.

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Engaging Hold Mode at 75%. Note there are 88 miles to my destination, with 39 miles of all-electric range available


In Part 1 of this post I calculated that by engaging Hold Mode at 75% SOC the i3 should be able to climb essentially any mountain pass in North America, so long as one keeps the gas tank filled. What isn’t visible in the photo above is that Donner Pass, a 7,228 foot climb, is between me and my destination; it is time to put my hypothesis from Part 1 to the test.

With Hold Mode engaged, as one drives the i3 the REx keeps the battery SOC constant at the level set.  If driving conditions are such that the REx (due to its limited power output) cannot keep the battery SOC maintained, then energy from the battery makes up the difference and the battery SOC falls commensurately.

Soon after leaving the CCS charger in Sacramento and engaging Hold Mode at 75% SOC I found myself once again in Auburn near where I had turned around just 90 minutes earlier during the Apple Pie Test.  It was time for a lunch stop.

As expected the battery SOC falls as elevation is gained
As expected the battery SOC falls as elevation is gained
The photo above was taken at my lunch stop in Auburn. Note that the SOC has fallen 4% to 71% at 1210 feet elevation (1160 feet of gain).  If I had stopped the car and let the REx run sufficiently long, the SOC would have returned to 75%. But that would have both taken time I didn’t want to spend and defeated the purpose of the Lederhosen Test. So, after a quick bite to eat I got back in the car and re-engaged Hold Mode at 71% SOC.

Leaving Auburn, I resumed toward my destination of Donner Memorial State Park 65 miles away in Truckee, California. The only thing between me and my destination was Donner Pass at 7228 feet, one more stop for gasoline, and the potential to run out of battery. But I had done my homework and was confident that I had plenty of energy left in the battery to complete my drive.

It was the perfect day for such a drive; the sky was a beautiful blue, the temperature was in the mid 70’s, the traffic light and SiriusXM’s Classic Vinyl accompanied me. During the drive I took pictures of the i3’s displays every 1,000 feet of elevation gain, but suffice it to say that the battery SOC slowly dropped in an expected and predictable fashion as I glided up the mountain’s slope. After 45 minutes or so I once again stopped to top off the fuel tank.

The battery SOC has fallen from 75% to 54% after climbing 5300 feet.
The battery SOC has fallen from 75% to 54% after climbing 5300 feet.

After refueling, Donner Summit was less than 30 minutes away. I found myself so absorbed in monitoring the progress of the battery SOC prediction that I nearly blew past the sign marking the summit!

The i3, with Hold Mode engaged, used a mere 31% (75% at the bottom of the hill less 44% at the summit) of its SOC to gain nearly 7,200 feet of elevation.  In simple terms, one can think of it as if the REx’s power output is used to propel the car forward, the battery’s power output is used to climb the hill.
The i3, with Hold Mode engaged, used a mere 31% (75% at the bottom of the hill less 44% at the summit) of its SOC to gain nearly 7,200 feet of elevation. In simple terms, one can think of it as if the REx’s power output is used to propel the car forward, the battery’s power output is used to climb the hill.
By using less than a third of its battery to gain those 7,228 feet, the i3 REx is obviously capable of much more. In Part 1 I asserted that the i3 with the European-style Hold Mode was probably capable of summiting any road in North America. After making the drive over the Sierra Nevada’s I-80, I believe that point has been verified.


The i3 REx with the European-style Hold Mode is more than capable of conquering Donner Summit simply by engaging the feature at the beginning of the climb and keeping the tank filled.  The US spec i3 REx is not.  But the implications are far greater than this.

The entire thesis of this post and the previous one is much larger in scope than “can BMW’s i3 make the drive to Lake Tahoe.” The thesis is much more than the car or the corporation. It’s about an idea.  A brilliant idea.

It’s about a transitional electric vehicle that the public can embrace without looking back, without asterisks and without range anxiety. The embodiment of that transitional electric vehicle is the BEVx class; to date only one car is made to that standard. It’s a brilliant piece of engineering.  Yet that brilliant piece of engineering is emasculated by regulations imposed by a governing body that should be championing it.

I’m surprised that Sir Isaac Newton hasn’t leapt from his grave and set his hair on fire.

The use case I have been passionately trying to demonstrate, that the i3 is fully capable of, may be an inconsequential corner case for the majority of owners worldwide.  But it is a legitimate use case and one that the many buyers consider. And people buy to the corner case, especially if it is their only means of transportation.

Until such time that adding energy to an EV takes as much thought and effort as adding energy to an ICE-mobile, technologies like the BEVx are going to be required to get the public to embrace electric mobility.

If removing the restriction on the operation of the APU is not made, the genius of the BEVx classification will never bear fruit.  That’s because even though the average driver does less than 40 miles a day, they also want the flexibility to take their car wherever they want, whenever they want. For this reason, PHEVs are about as “electric” as the general public is willing to go.

Once the current limitation of the APU software managing the SOC is understood by the public, the public will eschew the BEVx classification for PHEVs, such as a Volt. While that may be a better choice for the environment than, say, a Camry, the Volt driver will not be able to drive as much on electricity as if he bought a BEVx, such as an i3.

That’s why I’m writing; to beg CARB to Unleash the REx. It’s been said that the PEHV is the gateway drug to a pure BEV. If that is so, the BEVx has the potential to be crack — instantly addictive. Make it so.

Facts about my trip from Mtn. View -> Truckee -> Mtn. View

Left home with 100% SOC
528.2 miles round trip
246 miles on REx
6.6 gallons of gas purchased
Ended trip with about ½ gallon more gas in the tank then when I left
4.1 mi/kWh
4 CCS charging sessions totaling 62.8 kWh
0 Level 2 charging sessions
Arrived home on the REx (6.5% SOC)