BMW i3 REx – Guide To Reduced Power Operation, Range Expectations


BMW is fully aware of how the i3 REx performs under most all circumstances, yet we know that not all dealers don’t openly share this vital information with potential i3 REx buyers.

Above is a BMW-provided worksheet on REx operation.  The information contained is not confidential.  Actually, it’s found within the dealer training manual.

The idea is that the dealer passes the information along to potential buyers so that they can make an informed decision, but clearly this isn’t always the case.

We’ve now heard perhaps a dozen or so stories in which the BMW i3 REx enters reduced power mode.  Typically, this occurs unexpectedly and catches the driver off guard.  However, if the above info was openly shared, then this wouldn’t be a surprising situation.

Even knowledgeable automotive reviewers like industry veteran Chris Paukert over at Autoblog was caught off guard by the i3 REx’s power restriction.  We wonder…was Paukert provided with the information shown above?

Tweet From Autoblog's Well-Respected Executive Editor Chris Paukert - The Drive He's Referring To Is Over Flat Terrain (Petoskey, Michigan to Birmingham, Michigan) On The Expressway For Approximately 255 Miles With The Battery Depleted Of Charge When The Journey Began

Tweet From Autoblog’s Well-Respected Executive Editor Chris Paukert – The Drive He’s Referring To Is Over Flat Terrain (Petoskey, Michigan to Birmingham, Michigan) On The Expressway For Approximately 255 Miles With The Battery Depleted Of Charge When The Journey Began

Point is, the information is out there.  It’s BMW job to make sure that i3 REx buyers/owners get the right info.  The dealers have this knowledge, but it may be the automaker who needs to take action to ensure that REx owners understand the operation of this unique vehicle.

And yes…entering restricted power mode all of a sudden and without warning is dangerous, so this is a safety concern, which then falls on BMW’s shoulders to address.

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45 Comments on "BMW i3 REx – Guide To Reduced Power Operation, Range Expectations"

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110 miles on a full tank. +100, BMW needs to get this out, before it bites them.

“BMW needs to get this out before it bites them”

I believe they are doing a classic, hide the
facts in the “Fine Print.”

After you read your “Owners Manual” and your “Infotainment Manual” didn’t you read the “Graphic Details of Rex Performance Warnings?”

The Best way to avoid the problems that are being reported is to delay your acquisition
of a BMW until they have fixed the problems that they created with their self serving design.

And when it engage, was he driving @ normal speed or over 75mph?

Of the REX stories I read, a majority were about how ther were driving over 80mph and then experience a power drop. On the flip side, people reporting no problem typically keep their highway speed under 70mph.

In my case, the REX activate a low speed, but I was able to drive @ 70mph without any problem. Yes, the driver should be warn that it is about to engage, but I actually knew it was going to by looking at the Guess O Meter.

I will have to do a long drive soon and for me it is clear that if I keep my speed @70mph or under it won’t be a problem with the added benefit of having a longer All Electric range.

Should sales people be better at explaining it? Yes. But my experience was that they were already eager to tell all the negative sides of EV (which were not actually). The graphic above is self explainary and should be given to potential clients and new clients.

70 MPH would be under the legal speed limit in approximately 1/3 of U.S. states. Is having to operate at that speed acceptable when posted limits are higher?

and even where 70 MPH is the legal speed limit, we all know traffic goes a bit faster… I wouldn’t really drive the i3 on highways for extended periods of time.

@Eric, @Goaterguy, A teeny reminder: the speed limit is formally, the *upper legal* limit at which cars are allowed to travel under *optimal* conditions.

It is not a recommendation, and certainly not a lower-bound of any sort, below which “no driver should be ‘forced’ to operate” yada yada.

The reality the highway police almost universally chooses not to enforce this law on major highways does not change this basic fact.

It’s like jaywalking (which I just did across at least 2 downtown streets walking from the bus stop to my office). It’s all fine and normal until you get caught and thrown the book at – or worse, get into an accident.

In my experience, as long as drivers are human and cars are not perfect, a 75MPH speed limit is about as high as a civilized entity should allow before actively inviting trouble on its highways – and that too, only away from urban centers and when the road is wide open. And that still doesn’t mean every single driver should max out on that speed limit. Remember that stopping distance is proportional to speed *squared*.

Not to mention the substantially reduced energy efficiency even at 70-75 MPH, regardless of the car type.

Speed is NOT the only problem…

Try some big hills and even at 65mph or 55mph, it is a problem.

Try to cross the Sierra Nevada on hwy I-80 (even 18 wheelers are going at least 55mph) and climb to 9,000 ft and see what happens…

Having grown up in Reno and Sacramento, I’ve been over the Sierra’s hundreds of times. Several grades have dedicated truck lanes where trucks are going 15-20 mph and not 55. Additionally, Highway 80 summits at 7,239′ and not 9,000′.


Well if you drive over 75mph, there is a price to pay… it’s called ranged… Go fast and stop often or go normal speed and go further. It’s true for any car. More so for the i3.

If you always need more the 130/150 miles, the i3 Rex (or any other EV to exception of the Model S and the Volt) is not for you.

If you must got 80mph for a long period again EV are not for you (may be the Tesla, but you won’t be able to reach the next Super Charger). The Volt is still an option but you are pretty better with an ICE at that point.

I had a sport car before my i3 and for long drive, I put it on cruise @ 75mph and forget about it. In Canada speed limits are 65mph so I’ll drive around 70mph, I’ll get around 93 miles (and extend my drive with DCFC). I will this 4 to 5 times a year. The rest of the time, I’ll do short burst of highway, I will be 100% electric and I won’t tell you the speed I’ll be going 🙂

It always goes down to, know your needs and buy accordingly.

“If you must got 80mph for a long period again EV are not for you (may be the Tesla, but you won’t be able to reach the next Super Charger). The Volt is still an option but you are pretty better with an ICE at that point.”

The superchargers that I’ve used tend to be spaced 100-140 miles apart so at least in an 85 kWh Model S you can always make it to the next supercharger going 80-90 mph as long as you get enough range before you leave. Maybe if you went 100+ mph in the winter you could get into trouble. But I routinely drive 80 mph between superchargers on I5 (aka the flow of traffic), and never had a problem.

While I’m not from Michigan, i can read a map. I wouldn’t call it ‘flat’

i ran a quick elevation profile ( and found this:

Start altitude: 663 feet
End altitude: 777 feet
Maximum altitude: 1434 feet
Minimum altitude: 580 feet
Distance: 248.5 miles
Total ascent: 7789 feet
Total descent: 7675 feet

My guess is they’ll wait until they are sued. So is the reason the Rex version in the states has the engine come on with only 6% battery life is to get more CARB credits etc????

perhaps they want angry customers so they can go to carb and change the software.

Really CARB creating a catagory of cars that makes it tough to do road trips, so that people will have 1 bev and 1 ice vehicle is non-sensicle. The software and gas tank restriction is to do just that.


CARB’s BEVx standard requires that the ICE not turn on until ~5% SOC remaining. In exchange, BEVx cars give the same number of ZEV credits as a normal BEV; EREVs (and PHEVs) give less.

After my 3-day experience with the car, I wouldn’t hesitate to take it on a trip from Dallas to Houston, for example. yes, I’d be keeping it at or below 75 mph. And I’d be staying in the right lane. But I don’t think it would be dangerous. And yes, I realize I’d be stopping for gas several times along the way.

Dallas to Houston is pretty much mostly nice and flat…

But isn’t i3 REx designed for CARB credit? California is NOT always nice and flat, especially going east-west.

So if we put this car on a 5% grade at 65MPH:

After the car goes into RE mode, how many minutes will the car go before it hits PPR?


After it goes into PPR what will the speed be?

You’ve been reading my mind.

That detailed chart on the right, still doesn’t tell you what *actually* happens.

Say you are on the road at 65MPH and the REx kicks in. Will you be able to continue at 65MPH without weird side-effects until the gas runs out? Or will your battery gradually drain towards the red as the gas depletes?

All in all, sounds like the Gen 2 Volt if its EPA range comes out close to 60 miles, can blow the REx i3 out of the water.

No way the 2016 Volt will be 60 miles EPA. 45 tops.

The 2011-2015 Volt blows the i3 out of the water, simply because it has adequate power and range on gasoline.

If you are going to do a range extender, it should be properly engineered to operate like a normal car.


And what happens to REx power output at 3,000 ft, 6,000 ft and 9,000 ft?

Those are the points of which the ICE will drop signficantly portion of their power output.

If the REx loses about 30% of its power output at 9,000 ft, can it still keep up with the electric demand?

Law of unintended consequences. My understanding is that BMW lobbied for certain CARB rules to get more ZEV credits, and then crippled the i3 Rex to meet those rules.

Despite that I’d buy an i3 today if it were AWD and would have if it were FWD too. I rarely to never drive out of my metro area

Interestingly the dealer didn’t show me this data when I shopped the i3. I was going to buy the BEV but seeing this winter range the Rex is probably a must even for me who drives very little. 20F is our high temp for Dec Jan and Feb.
factor in battery degradation and clearly the BEVS will have trouble here after a few years.

The outlander PHEVS is having serious winter range issues too.

More and more the Volt 2.0 is looking like it may be my next car.

We’ll have to hear from European i3 drivers, whether their REx experience is less ‘crippled’, or maybe the differences are only nuances (20 miles more, slightly different thresholds). I suspect the latter.

So, we have a car with both a plug and an ICE, that sells for a premium price, that is potentially problematic for long-distance driving (speed limitations, frequent fuel stops).

Sounds like the perfect argument to have one BEV in the household for normal errands and (for most people) work commuting, and one Volt-like vehicle (or plain old ICE) for second car and long-distance duty.

How about just a Volt for all needs?

I think BMW should warn potential customers that they may lose power suddenly when driving the BMW i3 Rex in range extended mode at highway speeds above 70 mph.

One thing they could do is to have the instrument panel completely change when going into Rex operation. Then they could show a big battery gauge that shows as “battery buffer” and have it big and clear enough that the driver understands what it is. They should be able to see the buffer dropping and therefor understand they need to reduce speed to keep that buffer full. And at minimum they’d have a good idea when they start to get near the red-zone that the car is about to go into reduced propulsion mode.

Does anybody know the meaning of the word limit? It does not mean minimum. The minimum speed on interstate highways is 40 mph. At that speed, you are not only operating completely within the law, but you are doing more for the environment than any EV buyer.

I used to assume that people who were into EVs were concerned about climate change, and reducing our energy consumption. But I have been disabused of that idea for some time.

It turns out folks build enormous houses with PV, and drive big, fast, energy wasting electric cars, all the while polishing their green halos.

Haha, you mirrored my comment above. Friends, speed limit is the *upper* limit not the lower one…

Thanks also for the video, took me a while to make sure it’s satire, after all there’s no shortage of old white conservative talking heads on all continents, who say what this satirist is saying, but really believe it 🙂

As to dissing EV drivers: don’t draw conclusions about us as a group, from a couple of speed-related comments in some blog. Overall EV drivers certainly are environmentally-minded. Doesn’t mean all of us are aware of the various ways we waste energy. But in general, this community has its heart in the right place.

If your serious response to the concerns with the i3 REx is to say, “just drive under the speed limit,” you have already lost.

Any car that essentially requires you to drive under the speed limit will be immediately disqualified by the overwhelming majority of Americans. It’s basically a toy at that point.


Watched the video right up to the point where the guy says: “I don’t know what climate change is”. Then just switched it off. So is this the new Mantra. The other one is: “Well, I’m really not a scientist so I can’t say.”

Frickin’ pathetic

George, it’s a satire, albeit in the British tradition (which has inspired Stephen Colbert), by which you often don’t realize it’s a satire until you’ve been had.

although we are a small community, I think we all have different reasons for being EV proponents. Some of us care about greenhouse gases, some of us like the technology, some of us like the cost savings, and so on.

my guess is that excluding Tesla owners, the majority of EV owners around here are relatively environmentally conscious, and significantly more environmentally conscious compared to internal combustion engine drivers. I would also not be surprised if even Tesla owners are more environmentally conscious compared to people in their income group. Let’s face it, but Tesla owner is probably not going to drive a barebones city car.

personally, I became an EV enthusiast because I want the United States to get out of the Middle East. The environmental benefits are a bonus but not my primary reason for being here. I mainly ride my bicycle, partly to save the Earth but mostly trying to keep my figure! But when I do drive, I like to drive with the flow of traffic.

let’s face it, every single one of us has an extremely high carbon footprint when compared to people around the globe. Therefore, baby steps baby steps baby steps!

Unfortunately, having wasted the last forty years, what is needed now is giant steps…extremely painful, WWIII size giant steps. Any politician, corporate flack, or infotainment type who pretends otherwise screwing our grandkids for personal gain.

This Paukert appears to have pulled a Broder. As an auto journo he should know that the i3 is optimized for inner city use, not inter-city. Why would he take a car like the i3 on a high speed road trip and expect it to excel? what’s his beef?

if it’s optimized for inner-city use, then why bother with even making the REx?

After all, over the past several years some ~200k drivers of Leafs and similar BEVs have shown that 70-80 miles of range are plenty enough for intra-urban use.

Nay, the REx’s raison d’etre is to enable those inter-city excursions.

If it does it poorly, then BMW should just yank the whole thing out, then put some more batteries in the extra space to get the range closer to 100 miles.

As an owner of a Volt and a Leaf, I totally disagree. I mean, sure, if you live in a really small city then 80 miles is enough. But I live in Dallas/Ft.Worth and there are many times where I just say screw it and take the Volt because the Leaf would require stopping somewhere to charge. And being the state of our fast charging infrastructure around here is just bare minimum (if even that) then the Rex starts to look very attractive even for inner-city use.

Disagree on the Broder reference. In a Broder case, the energy capacity was not set before the trip.

The case with the i3 relate to how driving range of two energy stores (battery and gasoline) are reported to the driver. In particular having control over how each energy storage source is used. The issue is compounded in the reserve battery capacity in the battery is too low for the ICE power to maintain speed under normal driving conditions.

For reference FCVs also use a 4-8 kWh battery to maintain a level of stored power for normal driving when short-term demand exceed capability of the fuel cell system.

I have read on the internet of several accounts of drivers who have lost power suddenly when they exceeded 70 miles per hour on the highway. But in every instance they were the only one in the car. What if you have three or four people in the BMW i3 Rex going highway speed, with the air conditioning or heat on, would you suddenly lose power at a slower speed? The speed you will be able to maintain, would it be lower?

Heat would be even worse since the i3 REx uses resistive heat, NOT heat pump. So, the REx would have work harder to provide electricity so it can be burned into heat. No REx heat recovery is one of the biggest design flaw in my opinion with the i3 REx.

The ICE is basically a heater with some fringe benefit of providing power. Allowing all that heat to waste for the sake of cost saving is shocking to me.

With more people in the car, the rolling resistance will increase slightly but NOT signficantly enough at hwy speed. However, if you go up a large hill, then the impact will be far greater.

Even if the Rex wasn’t cripple here the instruments in this car are really terrible. As a leaf driver For 50,000 miles and a prospective i3 customer it’s easy to see, or maybe I should say hard to see the #s on the dash.
I showed my BMW salesperson the huge range remaining display and the 12 bar increments. And thn pointed to the tiny range remaining n the lower right of the tiny phone of a cluster display. I might buy one of these but I think the cluster might be the worst gauges in any car made . The Leaf has multiple warnings and looking back now , was very well done with the exception of the % of charge indicator being missing.

A detailed account of how the REx works and why it’s unsuited for trips in hilly areas was posted on Tom Moloughney’s i3 blog by a S.F. Bay Area i3/REx owner (and engineer). Part 1:

Part 2, Actual Bay Area to Tahoe trip results:

The only problem here is the misperception that the BMW REx vehicle is a hybrid. It isn’t. It is an EV with a range extender. When the the EV range runs out, you are “out of gas” so to speak. Thus, if REx is operating, you’ve effectively run out of gas and are fortunate to be moving at all. Sure, it’ll drive highway speeds but you need to recharge the car before attempting to climb I-80. It is the exact same thing as expecting an imminent stop when cruising at 90 on an empty tank of gas in your ICE vehicle. The CARB rules governing the REx are ridiculous. In fact, the rules lead to the exact opposite effect that CARB is supposed to be encouraging since requiring that the REx not come on until the battery is effectively empty will likely hinder the sale of EVs. The REx should be able come on as soon as you start the car. It should then do so based on the distance expected to travel. Operating this way, the BMW REx could allow 3 hours of highway driving at extremely high MPG. And based on total vehicle usage patterns, this would be… Read more »

Actually, I should not accuse CARB of attempting to hold back plug-in vehicle sales but these policy actions seem undermine rather than support their expected goal.