U.S. Spec BMW i3 REX: Smaller Gas Tank, No Range Hold, Limited Speed?

As anyone who has driven supposedly identical cars destined for different parts of the world will tell you, there are always a few key differences between how they’re set up for different markets. Traditionally, trim, standard-fit items, entertainment systems, engine specification and even physical dimensions can vary from country to country, with customers in one market often wishing they had the features offered as standard in another.

Are U.S. BMW i3 REx buyers getting a car with a smaller fuel tank, limited top speed and no range holding?

Are U.S. BMW i3 REx buyers getting a car with a smaller fuel tank, limited top speed and no range holding?

It appears the all-electric BMW i3 and its range-extended sibling, the i3 REX (BEVx) is no exception.

Just weeks away from the i3 U.S. Sales debut, BMW has been busy training staff from dealerships across the nation on its first mass-produced plug-in. As a consequence, the differences between the U.S. i3 and its European sibling is starting to show.

What’s more, the changes — specifically those applied to the i3 REx– won’t make everyone happy.

As BMW MiniE then ActiveE Electronaut and i3 reservation holder Tom Moloughney posted yesterday on his blog, information coming out of BMW’s official training sessions seems to point to some differences between the way the i3 REx operates in the U.S. and in Europe.

Smaller fuel tank

Most noticeably is the difference in gas tank size between U.S. and European i3 REx models.

In Europe, the i3 REx’s fuel tank is 9 litres — 1.98 gallons imperial or around 2.37 U.S. gallons. But, says Moloughney, U.S. dealers who have been to the training are quoting a fuel capacity of 1.9 U.S. gallons.  That’s an equivalent drop of 21 percent, or in other words, a range-extension of about 50 miles per tank instead of the 80 miles or so offered by European models.

The reason? We’re not sure, but here are two possible explanations.

The first revolves around fuel bladders, although we’re not sure if the BMW i3 even uses them.

In a certain generation of Toyota Prius hybrid cars, the fuel tank contained a flexible fuel bladder, a flexible membrane which expanded and contracted in line with the fuel in the tank. Designed to control the evaporative emissions of the gasoline, it essentially rendered the fuel tank of certain model year U.S. Toyota Prius hybrids smaller than comparable non-U.S. market cars, which did not have the bladder fitted.

The fuel tank capacity discrepancy could be due to a fuel tank bladder -- a different approach to GM's Chevy Volt fuel tank pressurisation.

The fuel tank capacity discrepancy could be due to a fuel tank bladder — a different approach to GM’s Chevy Volt fuel tank pressurisation.

What’s more, the presence of the bladder helped Toyota certify the car as a low-emissions vehicle, since it helped eliminate air — and thus errant hydrocarbons —  in the fuel tank.

For its Chevrolet Volt extended-range electric car, GM took a different approach, pressurising the fuel tank. Like Toyota, it needed to in order to classify the Volt as a low-emissions car under CARB emissions regulations.

It’s possible — although unlikely — that BMW has decided to opt for Toyota’s now discontinued bladder model, the difference in fuel tank size being about the same as the difference between a tank with or without a bladder.

The second potential reason — which is more of a confusion than anything else — could be related to nothing more than a simple misunderstanding.

You see, there’s a difference between UK (Imperial) and U.S. gallons. In its original specification, the 9-litre BMW i3 REx gas tank equates to 1.98 UK gallons, or 2.4 U.S. gallons. It’s conceivable that someone at BMW mistakenly converted the gas tank size of the U.S. market car by using UK rather than U.S. gallons.

Range extender is just that

As BMW previously explained several times, the U.S. market i3 REx won’t have the ability to operate when the car’s battery pack is fully charged in a range-holding configuration. Having driven an EU-specification car, we can confirm that option does exist on this side of the Atlantic.

Forget about charge hold mode: U.S. customers aren't getting it.

Forget about charge hold mode: U.S. customers aren’t getting it.

In the U.S. however, BMW has confirmed the range-extending engine won’t kick in until the car’s battery pack reaches 6.5 percent state of charge. At that point, the range-extending engine will turn on, operating purely to maintain that level of charge.

It won’t Moloughney says, bring the battery pack above that level of charge. Nor will it run when the i3 is stationary. This is different to the Chevrolet Volt, which will run its gasoline engine to recharge its battery pack back to half-full when ‘mountain mode’ is engaged.

Moreover, the only way of disengaging the range extender will be charging the car’s battery pack up, which Moloughney says is in direct contradiction to what he was told last year by a BMW executive who said it would be possible to override the range-extender and use the final few percent of battery power if you knew you’d make it to your destination without it.

70 mph limited speed

Finally, Moloughney reports dealers telling him, the i3 REx will be limited to a top speed of just 70 mph when the range-extending engine kicks in. While he disagrees with it, saying he’s talked to European i3 owners who have driven faster in range-extended mode, this does tie in with a UK report from last year which claimed a BMW i3 REx slowed to just 44 mph on a steep freeway incline when its battery pack was depleted and its range-extending engine was running.

Since we’ve yet to test the BMW i3 REx in that particular situation we’re going to reserve judgement, but it doesn’t necessarily bode well with BMW’s sporty image if the i3 REx does indeed limit speed when the battery pack is empty. Even if that speed is by most standards, just above or just below the legal limit.

More clarity needed

As we covered earlier this week however, it’s worth noting that dealers aren’t always the best folks to ask for information when it comes to EVs — even if they’ve just been on an official training course.

For now then, we’d advise waiting a little longer for early BMW i3 owners to receive their cars and give their own initial reports on each of these issues before determining just what the U.S. specification i3 has or doesn’t have compared to its original European sibling.

Watch this space.


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  • vdiv

    Ok, Nikki Maddow, we will continue watching this space :pnnOr get a Volt instead.

  • nInteresting u2026 at just 6.5% SOC, the battery pack has a lower voltage and can not supply as much power compared to higher SOC (eg: 50%). Expect this is related to lower speed and acceleration capability in REX mode (US version). nnI’m curious if there is a threshold above 6.5% SOC that the REX will cut out? (without requiring the i3 to stop) While the REX won’t increase the SOC, there are senecio’s that regen can add more than a few % to SOC. eg: both California and New York state have a number of hills and mountains. nnIt would be a fun test drive, taking an i3 REX from San Jose, CA (or Stockton, CA) to San Francisco, CA and driving over the famous hills in afternoon traffic. The combination of hills and notorious stop and go traffic would make for a noteworthy driving report.

    • Alex

      I think the 6.5% if of 18.8kWh, so 1.2 kWh. However, there is an extra 22 – 18.8 = 3.2 kWh in the battery kept as backup, so the SOC the REX maintains is actually 4.4 kWh (20%) of the 22 kWh capacity (but it cannot use all that, only 6.5% can be used). It matters because at 20% SOC there is more power available vs at 6.5% mentioned above so I doubt the driving performance will degrade much. But the car will try to keep it that way by limiting consumption, hence the 70 mph speed limit (which I dislike a bit…).

  • philternent

    Hi. I am a UK driver of an i3 with rex. The range extender kicks in at around 6.5 mile battery range, I have driven for a further 30 miles like this, sometimes the range drops a mile other times increases, driving at 65-70 mph with heating off, one or two other passengers, up and down hills but not mountains. We can overide and switch on extender at any point below about 70% battery charge, which may be useful if you want to incorporate a fuel refill at a certain point in the journey but certainly not essential. For my purposes, after driving a leaf for 30 months this is an almost perfect option (5seats would be perfect). I have used the car every day for last 2 months, whereas with leaf I would have ended up using a shared petrol car for at least 4 x 100-130 mile round trips in same period.With the i3 rex you just use extender on last 20-30 miles, no problem. But you have saved driving first 80 miles on petrol. I expect to drive around 11,000 miles pa in i3 instead of 9,000 in leaf, with I would guess around 500 miles of the 11,000 using the rex . I have also filled a 5L fuel can up which is kept in front storage compartment, but I’m planning on abandoning that idea as realising not an issue where we are. Its a fabulous car to drive, very pleased!

    • Thanks for the feedback! I think U.S. customers will be envious of your ability to switch the engine on or off as required! nnIn the U.S., regulations have mandated that the engine only runs when the battery pack is empty, which is a shame. nnWould love to see you at our next UK BEVoB meet — https://bevobjune2014.eventbrite.co.uk

      • philternent

        Sorry cant make your event, I’m up near Scotland. I have tended to just let the extender kick in automatically when battery “empty”- not really empty- shows 6-7 miles range, and also has a reserve which doesn’t appear as part of the displayed battery charge-the car still drives normally if left to do this automatically and maintains the battery life at around 6-7 miles. I don’t think its a real problem having proved it by using and owning a REX i3. I agree Government interference is annoying, let the economics of the thing sort it out, in uK buying petrol costs 5 x that as charging by electric, so you aren’t going to use petrol unless you have to.

  • Sergio

    Your information is wrong!nCheck back with Tom. nGas tank is same size – US and Europe