BMW i3 REx Test Drive: “A Posse Could’ve Caught Me On Foot” While Driving Up Long Hill Road


BMW i3 With REx

BMW i3 With REx

Fox News recently reviewed the BMW i3 REx.

The extended test drive left the reviewers generally impressed with BMW’s range-extended electric car, but there was one issue that’s been documented elsewhere before.

The problem is the REx’s inability to maintain speed up steep, long inclines.  The reviewer describes the situation as follows:

“…but things really get interesting as the battery drains.”

“When it gets down to about five percent, the gasoline engine kicks in to maintain the charge at that level. You lose a little performance, but nothing you’ll notice if you don’t floor it….”

“I spent an entire day driving in this mode on every type of road, and it worked almost flawlessly.”

“The only hitch was when I came across the appropriately named Long Hill Road. It was a ski slope-steep ascent a little over a half-mile long, and by the time I got to the top I was out of juice and just putt-putting along at about 10 mph like a Conestoga wagon trying to get over Colorado’s Loveland Pass hauling a load of stolen gold. A posse could’ve caught me on foot.”

Traveling 10 MPH up a steep ascent really isn’t acceptable.  BMW promises to address this with software updates for all range-extended i3s.  The tweaks will allow the car to build up more battery buffer in anticipation of such climbs.  It remains to be seen how effective the fix will be.  Early beta testers of the tweaked software report mixed results.

Source: Fox News

Categories: BMW


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54 Comments on "BMW i3 REx Test Drive: “A Posse Could’ve Caught Me On Foot” While Driving Up Long Hill Road"

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I’m one of the beta testers and from what it sounds like, the software tweak probably wouldn’t have helped this person. In their own words, “I spent an entire day driving in this mode on every type of road, and it worked almost flawlessly.” So I’m guessing they were driving along on relatively flat terrain for a while “all day” as they say with the battery discharged and the REx running and they then came across a long, extremely steep hill and began to climb. This software fix won’t help in this situation. It does help if you are driving along, and your SOC is lower than 25% and you begin to climb a hill. The REx will then kick on and maintain the higher SOC – it won’t wait for the 6.5% threshold to be reached before it turns on. It will maintain a higher SOC for a greater buffer. However in this case, it appears the person was driving around all day in REx mode, likely whit the SOC around 6.5-7% and then decided to make this long, steep climb. No dice. This software modification will only help with a percentage of cases where the car can go… Read more »

To avoid this low power to the motor you will need to set the point that the Rex Petrol motor kicks in, change the setting from 5% to 10% or 20% try to find a setting that suits your needs.
The motor has plenty of power as long as it can get the energy from the battery.

Tom, since you are Expert on the I3, is it possible to have the motorcycle engine build up the battery while the car is shut off, such as at a restaurant without plug in facilities?

It’s a real shame that fishing for ZEV credits made BMW gimp the i3 REx so much.

An option to manually enable the REx to conserve battery, a bigger gas tank, and a slightly more powerful engine would’ve made the i3 almost perfect.

True, but I don’t believe it needs a more powerful engine. I’ve driven over 1,000 miles on the REx and it can really do just about anything needed except these long, sustained climbs, and that is because the SOC is too low when it begins.

As John Higham learned by coding the hold mode into his car, the i3 can climb any mountain in the US with the current motor if you were allowed to activate the hold mode as the European version can do. No more power is needed.

In the REX version will the software not let the battery drop below 6.5% SOC? On my calculations 6.5% is about 5 miles driving range. If you had the BEV i3 (no rex) and you arrived at the bottom of a 0.5 mile hill wouldn’t you make it to the top with normal driving performance?

IMO the rex should kick in at a driver definable point and do it’s best to keep the car above that SOC but if it drops below that there should be no issue. If you are driving in a manner that means you completely flatten the battery even with the rex running I would expect to pull over and go for a coffee while the rex charges the batteries. Is that not how it works?

It’s not that simple. Low SOC also means lower battery voltage, which drops your power down proportional to the voltage.

I am still waiting for that trip to be repeated in the winter (SF to Tahoe) when the weather is icy cold and you need heat during the long climb as well….

How about a bigger battery and no engine?

The extra weight of the Rex is 120kg so if the battery pack had an energy density of 120Wh/kg you could have an extra 14.5 kWh for the weight of the engine. This would give the i3 a range of around 150 miles the petrol Rex gives it a range of about 200 miles. Me personally, I’d rather have the bigger battery pack but BMW made a call and I think that is a perfectly defensible position.

(note I am assuming a pack density not the energy density of a cell which is higher)

I’m sure that GM and BMW will both be lobbying CARB to change the rules of BEVx to allow more flexibility of operation.

You got that right!

Unclear what you mean? GM does not need this for the Volt. They have all the power in hte Volt they need for long hills.

They still want/need HOV access in CA Scott. GM is undoubtedly continuing to lobby CARB for the continuance of the green sticker program. That’s very important. Without it, California sales would be severely impacted. More Volts are sold in CA than anywhere else in the US.

I didn’t read the part about BEVx, only lobbying CARB. GM obviously doesn’t need CARB to change any BEVx rules

From what I’ve read, BMW lobbied CARB to -create- the crippled “BEVx” category.

If BMW wants to sell a practical PHEV, then it can certainly do so, just as it does with the European version of the i3 REx, and just as GM does in the USA with the Volt. The reason BMW sells only a crippled version of the BMW i3 REx in the USA is because they are far more interested in getting carb credits than they are in selling large numbers of compelling plug-in EVs.

Exactly. In the US, the i3 is a compliance car for BMW purposes.

I totally disagree. An example of a compliance EV is the Toyota RAV4 EV.

Then why can I buy one here in Texas? What are they complying with that forces them to sell the car here? The answer is nothing.. They simply want to sell more cars. That’s not the nature of a compliance car.

Grins, No Tom, He does Not have it right.

From 2012 MY through 2013 MY, Chevy Volt EREV’s were Carb compliant if they bore the California required Low Emissions Package and had an E, F, G or H in the 5th position of the VIN.(Enhanced ATPZEV)

Model Years 2014, 2015 were designated(TZEV*)and Had specific engines:

The Compliant Cadillac ELR ERELC has a specific engine as well for TZEV*.

Here is what the California Air Resources has to say about this new designation for the 2015-2015 MY:

* Please note that the new terminology for Enhanced Advanced Technology Partial Zero Emission Vehicle (AT PZEV) is Transitional Zero Emission Vehicle (TZEV). TZEVs meet the same certification requirements and qualify for the Clean Air Sticker.”

Link Goes To California Air Resources Board Website-

Finally, here is the generator (Range Extender) outputs, peak, on the GM Products Verses The BMW Product.

2015 MY BMWi3 R-ex 25,000 wHts

2011-2015 MY Chevy Volt EREV 55,000 wHts (MGa)

2014 Cadillac ELR ERELC 55,000 wHts (MGa)

2016 Chevy Volt EREV 75,000 wHts (MGa)Est.


Thomas J. Thias

Sundance Chevrolet Inc


“An option to manually enable the REx to conserve battery, a bigger gas tank, and a slightly more powerful engine would’ve made the i3 almost perfect.”

That is available. It is called a Chevrolet Volt 😉

…. and it costs $10,000 less….

Brian, from what I gathered, just LOVED the car, especially with his LEAD foot. hehehe.

I also liked the car.

THe bugaboo around here is the, in effect, unbelievably huge power robbing heater.

Its like building an all electric house in Buffalo. You’ll have nothing but trouble and high bills.

Now if those ‘cold weather heat pumps’ could be made to cost less and weigh less, than there might be promise for both issues.

But Brian definitely would hate the REX, unless it could run ALL THE TIME, even when off, to get ahead of Brian.. hehehe. But I think at some point you’d have to do something about that gas tank.

The QC is the way to go, the REX sounds like some costly silliness.

How much start up pollution does it make anyway and is it subject to emissions checks, how often are oil changes, etc?

“How much start up pollution does it make anyway and is it subject to emissions checks, how often are oil changes, etc?”

It doesn’t with special catalytic converters that is attached to the engine body so it will warm up as soon as the exhaust is hot (which is almost instantly).

It is funny that BEV purist likes to ask how often is the oil change…. Oil changes on BEVx or EREVs are as few as 1 every 2 years… Which is effectively nothing comparing to conventional cars…

If a street is that steep, that it needs to have warning signs to drive in low gears for ICE cars, I don’t think going only 10 mph for some short time is that bad.

By all accounts gm got that right with volt 1.0. I’ve never heard of limping up a mountain Ina a volt. Something to keep in mind depending on where you live. I can’t see it keeping me away but I’m waiting for a 7 seater e-rev anyway.

Not sure why this is such a surprise to many. The i3 Rex has a battery capacity for X number of miles, and after that, it’s only got as much electricity as the somewhat loud gasoline engine can produce, which will slow the vehicle to keep pace with production.

But the Volt is a PLUG IN HYBRID and the gasoline engine can also TURNS THE WHEELS so going up a steep pass with an empty battery is no problem, because it can just run using the gasoline engine. And with the next gen offering a 50 mile EV range and over 40 mpg, the Volt is the much better option for those occasional trips over 50 miles.

Chevy Calls the Volt an EREV (Extended range electric vehicle), not a plug-in Hybrid. There’s a reason. In a Plug-in hybrid, like the Prius plug in or the Ford Energi models (C-max, Fusion), The engine and electric motor combine to provide full performance. Separately they can power the car under a light load, put when there is demand for full performance, they must work together. With the Volt, the Electric motor is designed to provide maximum performance by itself. Yes the engine can drive the wheels, but it’s not geared to provide torque for a steep climb, it can power the wheels in a less demanding situation like maintaining speed on a flat terrain highway. The Volt reverts back to using the electric motor anytime a heavy demand is put on it, like a steep climb. So a Volt with an exhausted battery would under normal conditions encounter the same problem that tripped up the BMW in this article. Chevy engineers realized this issue and included a feature called mountain mode. If the driver knew he/she would have to climb this hill with in Charge Sustaining mode, they have to engage mountain mode about 10-20 minutes in advance of the… Read more »

However the Volt’s range extender puts out 60kW where the i3’s only puts out 25kW.

Partly balanced by the difference in vehicle weight.

With a single driver, the Volt 1.0 weighs about 25% more than the i3 REX. The Volt’s generator is still far more appropriately sized for steep hills, but the lighter weight of the i3 does help it a little (in the best case scenario).

25% more weight, 250% more power. That’s an order of magnitude.

Great answer,
just one little thing I would like to add :
“If the driver knew he/she would have to climb this hill with in Charge Sustaining mode, they have to engage mountain mode about 10-20 minutes in advance of the climb.”

This delay is just a recommendation.
From my experience, you can still engage mountain mode at the foot of the hill, or even during the climb.
The car will use any opportunity it can find to increase the energy buffer in the battery, like any slow down, hairpin, traffic jam, etc… And you can feel the difference, even hear it as the engine rpms go down very quickly, once the car estimates it has enough energy buffer based on your driving style.

Well said. TO me, it sounds like the car realizes its in danger and Scotty from Star Trek is down there pushing all those cylinders as hard as he can to make it up the anticipated Klingon Hill.

“I’m giving it Aull she’s Gought, Capt’n !!!”

“But the Volt is a PLUG IN HYBRID and the gasoline engine can also TURNS THE WHEELS so going up a steep pass with an empty battery is no problem, because it can just run using the gasoline engine”

*sigh*… So much ignorance and misinformation in the world about the Volt…

Your first point is just silly and I don’t think we need to argue over about PHEV vs. EREV again here.

Your 2nd point is false. Connection to the wheel has NOTHING to do with the fact about Volt power. Volt power is primarily the electric motor. Volt’s engine doesn’t almost nothing to help the hill climb.

In fact, if you take a Volt with empty battery and starts the climb on I-80 to Tahoe, it will reach a point just before the Donner’s pass that car will go into “power cutback” mode where the generator can’t keep up the climbing.

This can ONLY be cured if you engage hold or mountain mode before the climb started…

You have to remember the author of this article said it was a half mile climb. That’s not a very long climb.

LOL, you got that right.

It is at 10mph. 🙂

“But the Volt is a PLUG IN HYBRID and the gasoline engine can also TURNS THE WHEELS so going up a steep pass”

Actually when the Volt needs lots of power, it operates as a serial hybrid.

The difference is that the Volt is designed to handle a much wider range of operating scenarios like steep grades, when compared to the i3.

BMW should step up and make a change before they are forced to by a recall ( cars that slow down unexpectedly are unsafe) It will be interesting to see who wins , NHTSA, or CARB , Carb says must use more ev than gas, NHTSA says car is unsafe and must use more gas……

The BMW i3 Rex is not road worthy. It can not maintain highway speeds over 70 mph on level ground and it can not climb a hill that is 1/2 of a mile in length in Rex mode without loosing power unexpectedly. Is this the look of future mobility?

So let me get this right.. The i3 Rex is not roadworthy but the Nissan Leaf, Ford Focus EV, and just about every other pure BEV on the road IS somehow road-worthy? The i3 Rex can do everything those cars can do and MORE.. How is adding MORE functionality to a car make it not road worthy?

David, all the cars you mentioned do not loose power unexpectedly. The BMW i3 Rex does. That is why it is not road worthy. The BMW i3 is road worthy. The BMW i3 Rex is not. It is important that you understand the difference. There was a US auto manufacturer last year recalled thousands of cars because the ignition switch would shut off unexpectedly. Resulting in a sudden lost of power that caused 13 deaths. The same thing can happen with the BMW i3 Rex. Do you understand now why I would say it is not road worthy?

Nope. I don’t see. I think you are just biased against the car. I drove one on Rex for an entire day and had no issues with it. And if I owned one I’m sure I’d be aware of the possible issue if I were driving on Rex on a long uphill climb somehwere and would plan accordingly. Then again, if I had one I’d probably only be using the Rex 4 times per year.

To me, the BMW I3 as arriving in the States, appears to be ‘Designed by Commitee’.. Of course, it was: A committee at BMW decided the 2 cyl engine should rarely run, and then a FILL UP (2 gallons) would only make the car go as far as it would had the added weight been used for more batteries.

So you end up with a car that truly would have been better being all electric, since if you are only expected to refill the gas tank once per trip, why not just have an equivalently sized battery to begin with, and skip all the ZEV gasoline nonsense?

And then as I’ve noted elsewhere, cold weather probably knocks those numbers down to 1/3 of what they are in moderate weather.

So until they tweak things a bit, no REX in my future.

Tom M- any thoughts you might have of jumping ship and getting a Bolt? What would it take for that to happen?

BMW should have never released the i3 on the public. It is under-powered and not worthy of the BMW badge. For all you that think it is road-worthy try driving it from Denver to Vail, it is under 100 miles, well within the range of the i3 REX. There are hundreds of other drives under 100 miles across the US that i3 REX owners would not make either. Seriously, Wait for the Tesla Model 3, which will be out in two years and not have such silly problems.

The Model 3 will have other problems – first and foremost: becoming a reality.

So building a five billion dollar battery factory is not a reality? The Model 3’s design and features are still being finalized but it will happen. That is like saying the iPhone 8 will never come out. It will be a reality. Whether it is successful or not is another discussion, but based on the Model S, it will again be a market leader by a big margin.

You have no assurance the factory is going to actually provide Tesla what it needs to compete and dominate in the mid-$30k price range. How do you know their batteries will stack up against other batteries – will they be more expensive to build to start with; will they have chemistry competitive with others?

Or will it be a gigantic flop, Elon’s Ishtar?

I think most points here are valid. The i3 itself lacks WARNINGS of the impending power loss….. A gross error on BMW’s part.
The well designed Leaf has prominent audible and visual indicators there is a power loss imminent. A recall is inevitable, voluntary or mandatory is the only question.

This car is dangerous with the REX and should be recalled. It’s only a matter of time until someone is hurt in an accident because their i3 REX suddenly lost power and got creamed.

Faulty GM ignition switches has that company in court right now….

I had a Leaf, I now have a BMW i3 REX. I live in cold MI. Both cars have limits. Both cars are a means to get from point A to point B. Both cars are EV’s.

The i3 is an EV with an ‘optional’ range extender.

EV owners should know better to even encounter such situations on any trip at or beyond its range.

I think warnings at point of sale and firm warnings on the dash and speaker (like the Leaf) would be sufficient.

If your trip is that challenging then you need a different tool for the job. The REX is a generator to get you home when you are puttering about in ‘the city’. If your ‘city’ is that hilly you have, and always will, need a different tool for the job. An EV never made sense in that terrain anyway. 2.5 kwh in those parts put the car on par with a PHEV like prius, volt, or even regular hybrids.