BMW i3 REx Road Test Yields 34 MPG, Plus Noise Levels Of The REx In Operation (video)

APR 2 2014 BY JAY COLE 37

BMW i3 Nets About 34 MPG In Spanish Test Drive

BMW i3 Nets About 34 MPG In Spanish Test Drive

With the first BMW i3 landed at port today in New York, the good fellows over at ForoCochesElectricos have done something we have longed for here in the United States for quite some time – thoroughly test the BMW i3 REx.

More specifically, put both an MPG number to the BMW, but also a sound to it – after the battery has been completely exhausted.

The BMW i3 REx Does A Good Job Of Keep Engine Noise Outside The Car

The BMW i3 REx Does A Good Job Of Keep Engine Noise Outside The Car

As for the efficiency, a 100 km trip would net a result of about 7 liters of gasoline, which works out to be 33.6 miles per gallon.  ForoCochesElectricos explains the result thusly (translated from Spanish):

“For consumption we have filled the tank of i3.  A deposit for up to 9 liters. We conducted a driving circuit including a stretch of 17 kilometers within the city and a stretch of 19 kilometers by highway, running exactly 100 miles km. Always at legal speed, both 50 km / h maximum in city’s 120 km / h on the highway.  All in a circuit.

After 100 kilometers, back to the same gas station to refuel. And refuelled to full with 7.68 liters in total re-introduced.  We can put a margin of error of 10%, as the filling in this second occasion seems to have been to limit the capacity of the tank, which would give us a figure of about 7 liters per 100 kilometers.”

As for the BMW i3 REx’s abilities when the car has been juiced, they had some issues under extreme conditions.  While driving 120 km/h (75 mph) before a rather steep slope, the BMW has lost 50km/h (31 mph) by the time it had reached the summit.  Starting from 60 km/h (37 mph) netted them an end result of about 30 km/h (20 mph).

The tester does note when used normally that if the BMW i3 “gets some wind” on the flat area with the battery depleted, “within seconds we have new energy to circulate normally.”   Morale of the story?  Don’t completely exhaust your battery at the very bottom of a mountain.

Video Below:  Sound of the BMW i3 REX operating with batteries exhausted – both from the inside, outside and at a standstill

There is a heck of a lot more of the review over at ForoCochesElectricos to check out … just have your online translator handy if you don’t read Spanish! — Hat tip to Carlos

Categories: BMW


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37 Comments on "BMW i3 REx Road Test Yields 34 MPG, Plus Noise Levels Of The REx In Operation (video)"

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Wow! That is loud.

Yeah, it is kind of loud.. But I think as seldom as I’d be using it, it wouldn’t be an issue. I rarely use the ICE in my Volt as it is, and the i3 has almost double the EV range, which would make engine use even that much more rare for me.

W/the carbon fiber body, I expected better MPG in RE mode.

It sounds like a portable generator. Yeah, I know, that’s essentially what it is, but I would have expected a little smoother note, especially since this is a BMW motorcycle engine.

The motor is not only loud, but it sounds rough and unrefined — just “cheap.” The sound reminds me of the old German “Trabbis” ( and not of a BMW motor bike.

The ICE may be merely a battery backup, but when you pay $40K+ for a BMW, shouldn’t you expect a little bit more noise insulation? People shouldn’t turn their heads b/c of the motor noise…

Great, In the USA spec you have no choice of when to activate the rex. So at some super low SOC 5% ? the rex activates and if you have a climb ahead…… put the flashers on and stick to the right.

I want to say I heard the US version kicks the REX on at 20%. If the REX can keep the batteries charged to around that level, you should have plenty of power.

They had to have the engine come on very late, around 6%, to try and qualify it as an EV in California… The gas tank range also couldn’t be longer than the battery range…


Now that I’ve read this, it sure makes me feel better about the Chevrolet Volt as it’s fuel economy is about the same running the range extender. The bright side is, you still have ample power in the Volt mountains and such.

Not even close to the Volt. I just returned from a 600 mile trip where I got 43 MPG on ICE only (ignoring the electric miles). 70MPH, level road, fully loaded car with three people, 80F. The i3 REx MPG is looking to be pretty disappointing.

Yes indeed. How is it possible that BMW created an inefficient engine with insufficient power. It’s just not… BMW?

The way I see it the gas engine is only for emergency use/a backup, on the very odd change that the EV runs low on power and no plug is available.

I don’t see buying an extended range EV if a daily or ‘normal’ commute is longer than then battery range.

If that’s the case the consumer is trying to use an extended range EV as a most inefficient/less capable plug-in hybrid that it was not designed to be.

Dr. Kenneth Noisewater

For Volt, the range-between-charges where it still is more efficient than a conventional hybrid or diesel is about 80-90 miles.

Not to mention that at 40mpg (60mph would easily give that EPA rating), the Volt is still decent even in extended range.

viva Carlos Morto BMW!

And to think that BMW was comparing the i3 with a Tesla! Let us see what the i8 will do? hahhahaha

Citation needed

There a a few things to consider in this review. Such as what is the altitude at which its being tested. What is the octane level of fuel being used. Is the REX being used in accordance with the recommendations. For eg not when battery is completely depleted and its in emergency get you home mode.

Right. They seem to be testing the extreme and it would be nice if they set the S0C higher which you can do outside the USA. It would be like using the Volt to climb Pikes Peak without using Mountain Mode (~40% SOC) and instead use normal (~20% SOC).

Great, so the truth comes out. Having the engine come on at 6% state of charge is a limp mode fiasco that can only hurt the reputation of other plug-ins that don’t have this issue. Thanks BMW. Since Rex no longer qualifies as an EV, they should quickly make a change so the engine comes on at 15-20% state of charge, and put in a larger fuel tank… Or bring over the Euro version thst has the manual button to turn the engine on earlier…


That pretty much sums it up in my book also.

The Volt is still the best option out there.

I know it only applies to when the rex is used and the car will mostly be driven in ev mode, but a combination of 7l/100km does not seem that great.

That is what I got in my old 1997 four-door honda civic hatchback.

ha… those crazy euros and their “round abounds”…..

Dr. Kenneth Noisewater

Wow, that economy is really poor! They probably should make an additional battery an option to take up that space.

The generator noise reminds me of the Prius engine rattle problem that is on going. I must admit once inside the cabin of the i3 it didn’t seem to be that noticeable. I wonder what type of muffler is being used?

I would prefer either: 1. 65 miles AER and an RX & fuel tank that can take you anywhere.
2. A pure BEV with at least 150 miles range.
I think the BMW I3RX will still meet many people’s needs though, just not mine.

Too bad they didn’t put in a bigger battery instead of the REX option. It sounds like a scooter. That’s not going to go over well in the States.

You can’t compete with an 80 mile range anymore. Sounds like BMW is not really trying to make anything beyond a compliance car.

Now we know why the Los Angeles Auto Show only provided Non-Rex cars for the public test drive. Among the many reasons in a long list of Rex failures,,,,, 30, i3’s with Rex running would have rattled the sleepy downtown like a Harley Davidson Convention!
Every camper understands that Honda and Yamaha, make the quietest generators,,the Rex sounds like a portable Generac.
Don’t expect happy neighbors or steathy returns late at night. LA, even prohibits leaf blowers because of decibel levels,,,the Rex, may be prohibited within City limits!
Laughing,,,,,,,,,but truly disappointed!
Not a day for complements for GM,,however the Volt is the sophisticated Range Extending technology leader.
BMW spent all of it’s money building a carbon fiber/plastics plant and ran out money to addess “range anxiety”, in a way worthy of it’s automotive reputation.

The noise seems to be a non-issue since it is really only the noise INSIDE the car (which seems very minor) that really matters. Heck, stand outside a normal ICE car by the front and back…pretty noisy. I will say the noise isn’t a “fun” noise (i.e. it’s no idling muscle-car).

Like virtually ALL EVs, this car will be appropriate for some and not for others. The Volt (which I won) probably walks a better balance for usability in general, but again, it all comes down to whether it is right FOR YOU.

Some folks will value the higher performance of the i3 over the greater usability of the Volt (as an example).

Seriously… aside from hard core BMW fanatics, who would buy this car over a Chevy Volt?

I have said that BMW did a good job at this “concept” but there are some excution issues.

1. The motor sounds “cheap”. For a BMW with a price tag, it could have sounded better.

2. The concept is still good, but BMW could have easily made the engine slightly more powerful to about 80HP and it would have made a difference in those hilly situations.

Thanks for the translation link. Makes it clear that the reviewer actually comes to the conclusion that the REx is actually the way to go, for a variety of reasons:
1. “Lawnmower” noise when Rex is running is only heard outside, not inside.
2. Limited MPG with the REx is not really an issue because you should only be using the REx on a very infrequent basis.
3. The offset to “range anxiety” that the REx provides is worth it.

Engine sounds like a Traktor. When a bigger battery comes rex is pointless

BMW should offer an option of instead of the REX; put an additional pack in it’s place.

this is so loud that it makes an toyota echo or even any car sound like an ev
true story yesterday i was walking home from uni and this echo just when by and it was quiet

Interesting I have a BMW i3 REX and have just over 800 miles on it. My roundtrip daily commute in the San Francisco Bay area is 58 miles each way and on a full charge I’m averaging 78 miles before the REX kicks in. As for noise when I first got it I made the mistake of putting regular low Octane in and it was noisy, going back to premium and high octane did help reduce the noise of the REX.