An Aerospace Engineer from the UK Compares the i3 and the i3 REx

 

Lucas flying formation in the Crimea

Lukas Willcocks is a member of the BMW i3 Forum and when I noticed that he posted about having the opportunity to take both an i3 and an i3 REx each for 24 hour test drives I asked him if he wanted to offer his thoughts and comparing them here. What I didn't know was that Lukas is an aerospace engineer. A few of my friends are engineers and the one thing I've learned about them is not to ask a question about something without expecting an answer that involves thoroughly explaining every aspect of the subject. Well, I found Lucas is not very different from my friends! :) His response was about three times as long as any post I've ever put up here and below is actually the condensed version! Warning: We're going off into technical geek land here folks! Special thanks to Lukas for the time and effort he put into this guest post:

To REX or not to REX: 24h with the BMW i3 BEV and another 24h with the BMW i3 REX:

Greetings from darkest Lincolnshire in the English Midlands. Winter this year is mild but very very wet and windy! Educationally, my background is in aerospace engineering but long before that I helped my father fixing old Land Rovers in the Kalahari and later Fiat Twin cams and VW GTis in the EU. I'd always found rally and race cars exciting and in recent years had the privilege of racing in historic motorsports with a 1969 Lancia Fulvia HF.

Colin Chapman (of Lotus racing car fame) is quoted as saying to his engineers “add lightness!” In fact the quote is from Sir Geoffrey De Havilland who gave the world the amazing wooden composite Mosquito WW2 fighter bomber- a machine that could leave fighter aircraft for dead. He also pioneered the first Jet Airliner the DH Comet 1: http://en.wikipedia.org/wiki/De_Havilland_Comet

Aerospace is about efficiency and optimization for specific roles. Whatever the debate on the environment, the world is attempting to move towards more sustainable living. Only 8% of the planet is suitable for arable farming and we all hate traffic jams. Conurbations are increasing at an alarming rate. My old home of Gaborone Botswana had just 40,000 people in the 1970s – now it it has well over 250,000. That country (the size of Texas or France) had 10 miles of tarmac road. Now it has the Trans Kalahari highway!

No cyclist or pedestrian likes petrol or diesel fumes. Electric cars are seen as a way of improving air quality in built up areas. That's all well an good as long as folk don't claim they are emission free vehicles! Most countries still rely on coal fired power stations and acid rain and CO2 is still produced when an EV is used. Even California is not 100% Solar PV / Wind farm dependent.

What is the most efficient means of getting from A to B? An interesting question and much depends on the task – is it to transport 40 tonnes of produce to market 1000 miles away or 2 miles to the grocery store to pick up some tomatoes for lunch? I recall a study that said even cyclists put out at least 15g/km CO2 based on toast consumption!

Intro over!

My thanks go to Hamish of BMW Soper in Lincoln UK who provided the i3 BEV in white which was fitted with lots of toys! And also to Chris Whitmore of BMW Statstone Derby UK for the loan of the grey i3 REX.

So how did the BEV compare with the REX?

That is the ultimate question on most potential owner's minds. Interestingly both cars when fully charged used the same amount of energy on the 29 mile commute to work. The BEV was quick but it's advantage over the slightly heavier REX was not noticeable in normal use.  Both cars had the same tyres front and rear so there was no Cd advantage for the BEV either. Unless you go to the Drag Strip regularly, I very much doubt any driver would notice a difference between the BEV and REX in acceleration terms. If anything the REX felt a little more planted in the corners but this may have been subjective. The rear motor/RWD layout allows far more steering angle than a regular vehicle so the turning circle is very tight at low speed. In muddy conditions it is possible for the traction control to give up and the tail does wag a little if you are too enthusiastic with the go faster pedal.

The biggest change is when you get down to around 6 miles of range. In the BEV there is mild panic even in Eco Pro Plus mode. In the REX the motorcycle engine kicks in with an annoying drone but it is not really noticable above 40 mph.  Some were concerned about speed restriction reports when the REX gets down at lower battery charge levels. I tried 0-50mph max acceleration and this seemed unaffected but there was on screen advice to go easy on the throttle pedal to enable battery charge level maintenance. It could well be that 70 mph uphill on a freeway would not be sustainable at these lower charge levels. That said,  my return journey was with REX activated manually at around 30% SOC. It did not maintain it precisely but achieved around 27% SOC over the 29 miles. Refueling was done at the same Shell station with same grade of petrol - tank was topped off both before and after commute. Economy on REX is not that great but it is really there to get you home or to nearest fast charger.

My guess is the battery in a REX will be in a far better state than that of a BEV after 3 years of similarly hard use. The damage associated with running the LiON batteries to an absolute minimum are more likely to be avoided by the car that maintains charge at low levels.It should also be noted that when the doors are unlocked the charge goes down whether plugged in or not because displays and system heating are activated and run off the main battery.  This might be fixed by a BMW phone app for users who wish to configure for a trip whilst charging. Showing off all the gizmos to your work colleagues will also deplete charge! 

Overall I like the purity of the BEV and only wish it could better 60 miles in mild winter commute. If it could do 100 miles at 60 to 70 mph I would buy one right away. As it stands if committing to an i3, I'd have to go for the REX and downgrade on the options list.

Now for some thoughts on the i3 in general: 

What can we compare the BMW i3 with? Existing cars have come a long way since Henry Ford. On the other hand the past decade has seen an explosion in ULVs (unsuitably large vehicles) sold to consumers of a “super size me” culture. Now I am all for the old Range Rover V8 doing 16 mpg through deep Kalahari sands where a Ford F250 got just 8 mpg. However for the grocery store run?

That might be acceptable in Arizona but on cramped narrow British roads with passing places in hedgerows or London's residential road width restrictors? Bigger normally means heavier and less aerodynamic so the term gas guzzler still applies. How is it that in 40 years fuel consumption has not really improved significantly? Part of the answer is heavier structures and crash worthiness regulations but that's often an excuse. Take the Fiat X 1/9 2 seater 1970s mid-engine sports car – it featured 50 mph impact bumpers and roll over protection for the US market – they even rammed one with an AMTRAK ! It passed but then the Feds reduced the regs and Fiat lost out. However that small car was tough (apart from on UK salt laden winter roads) yet still much lighter than today's machines: http://www.sportsvogn.no/x19reg/story.html

A few visionaries still exist. VW developed the 3L cars – 3 litres of fuel for 100 km of travel. They produced the shortened Polo and called it the Lupo 3L with magnesium and Aluminium panels. Audi developed the all aluminum A2 which many have cited as an influence on today's BMW i3. The 3L version of the A2 was designed to carry 4 German sized adults and their luggage from Munich to Turin over the Alps with minimal fuel cost and low emissions. It had a Cd of just 0.25 – the same as the original 2 seater Honda Insight hybrid and weighed just 855 kg.

This has been my everyday transport for some 190,000 miles over the past 12 years: http://www.greenconsumerguide.com/audi_a2_tdi.php Sadly the car was poorly marketed compared with the less efficient Toyota Prius and productionceased in 2005. But not before an H2 and electric variant were prototyped. In 2010 DBM Energy claimed their modified Audi A2 could travel 375 miles at 55mph on batteries alone.

http://www.plugincars.com/claiming-battery-breakthrough-electric-audi-drives-375-miles-55-mph-without-recharging-99966.html

Sadly the factory and prototype burnt down.

VW have moved on into the extremely expensive ECO car with their impressive XL1 – but it's no longer a Volks-Wagen (people's car) at £100k !

http://www.topgear.com/uk/photos/vw-xl-1-we-drive-the-future-2014-02-03

Others have compared the i3 to Tesla. A bit like comparing a 1 series with an Aston Martin.

This review will look at basic everyday practicality and make some suggestions for BMW's further i3 development.....

External Colour choices:

Not a lot of choice. Mostly greys, silvers and one for the Dutch : orange. I don't mind the

contrasting black panels. One dealer suggested the i8 Protonic Blue might become available next year.

The biggest downside if you want orange is the extra you have to pay to upgrade the interior. Someone should tell BMW to have a look at Irn Bru (Scottish Soda – orange, black &blue can work!). Not such an issue in USA.

Interior space:

Many reviewers have posted that the i3 has an airy feel – at least from the front seats. I would agree that the large sloping front windscreen and uncluttered dashboard appears to offer more light and the high seating position reduces any bathtub parallels by giving a more commanding view of the road ahead. However, whilst the i3 is around 15cm wider than the A2, in the rear it has almost 4cm less headroom, 20cm less foot room and just under 7cm less elbow room. The larger rear side windows help to mask the latter somewhat.

The white i3 BEV had a white LOFT interior – nice if you never drive in the real world. The white carpets soon became muddy grey brown! The REX had the standard interior which was very practical.

I like the futuristic flat screens that appear to hang in space over the dash.

Whatever your view on the construction material, the anti reflective properties of the dash work well with the black bonnet rather like a 1960s Rally car.

The driving position is very comfortable and has a good degree of adjustment. The seat height shift is a little awkward compared to rival cars where body weight has to be lifted on the steering wheel before raising.

The seat heating is a very worthwhile option for winter driving and means you can save energy on interior heating.

Side bolstering of the front seats is minimal. Had the car been designed with conventional rear doors and without forward tilt on these front seats, maybe BMW could have gone for a fixed back sportier option like a Recaro Pole Position (just 7kg!).

Load space:

One disadvantage of RWD with rear Motor placement is the much high than normal load area and reduced volume.

(litres seats up /litres seats down)

i3: 260 / 1100 litres

A2: 390/1085 / and approx 1400 litres with rear seats out

A3 Coupe: 365 / 1100 litres

A3 Sportback: 380 / 1220 litres

A1 Coupe: 270 / 920 litres

Quite a bit of space is taken up with American sized Soda Cup holders between the seats!

Weight Saving:

BMW has made much about the lightness of the underlying CRP structure on the i3. They are to be congratulated for bringing this to a sub £26k (base model with £5k UK grant) production car.But it is still a heavy car even making allowances for the EV battery pack.

One wonders whether 19 or 20” wheels are more about style over substance – certainly a larger diameter spinning mass has a greater effect on vehicle dynamics. It would be interesting to know what each wheel design/tyre combo weighs.

Areas where lightness could be added:

1. Make it a 3 door or go for conventional rear doors with CFRP B pillar.

2. Go for 1 front wiper blade with full sweep. Remove rear wiper mechanism and install

better rear tailgate with aero screen cleaning. (NB: the front wipers DO NOT sweep up to 90 degrees so there are a couple of unswept patches either side at eye level).

3. Make rear seats removable like briefcase design in A2 and front seats fixed back like Audi TT Quattro Mk1.

5 Doors or 3 door with Access panels?

In terms of accessibility we have already seen reviews of the difficulty in releasing rear occupants with driver or front passenger in place. The suicide rear doors are a design statement more than a practical solution to rear seat entry/egress. Such an arrangement in a UK Supermarket parking space with an SUV either side, it could get too tight to let the kids out of the rear seats. In some ways a 3 door hatchback or Coupe might have an advantage, although those front doors tend to be longer. It seems odd that the designers made the front seats forward tilting and indicates that a 3 door option may have been in mind.

Some commentators have made comparison with the Mazda RX8. In both cases these sucide doors have had to be strengthened considerably and fitted with larger closing mechanisms and hinges to cope. From a weight and energy saving perspective this is a little absurd. Matters are made worse if a child seat is fitted in front without ISOFIX. Note the weight limit is just 18kg (40lbs) for an ISOFIX attachment so heavier children will require the seat belt attachment. This makes it impossible to open the rear door on the pax side if the child seat is up front.The deeper rear windows are good for rear seat occupants but do not open – not even to a vent position. Again why bother with rear doors? Make it a 3 door Coupe like the orange prototype or offer a CFP B pillar / Avant version with normal rear doors and hidden handles ( a la Alfa Romeo 156).

Aerodynamics - What a Drag!

The i3 has a closed front grill / kidney emblem and commendably flat under tray free of the usual incursions. But for an ECO minded car it is somewhat surprising that BMW did not strive to improve the Drag Coefficient or reduce the frontal area of the i3.

If you never go over 40 mph (London UK inside the M25) this isn't going to affect you. But most London workers live outside due to ever spiralling house prices and will likely need to use the Motorway (Freeway) network. Greater aerodynamic efficiency (and hence lower battery consumption) could have been achieved by replacing the BMW X5 like wing mirrors with VW XL1 rear view cameras or at least more compact examples. The Cd is 0.3 (about as bad as a 1992 Toyota Camry or 1993 Subaru Impreza). The i3 is much wider than most pure 4 seaters and the MPV styling and battery floor makes it quite tall. Frontal Area of 2.38 m2 x 0.3 results in a CdA of 0.714.

Compare this to a 2001 Audi A2 1.2 TDI : CdA 0.544 or 2013 VW XL1: CdA 0.279.

At 100km/h (62mph) the i3 BEV creates 326 Newtons of drag. The REX model a little more at 336 Newtons. The A2 a mere 257 Newtons.

More meaningful to the average punter is BHP absorbed by drag. Here we are not considering the drag from the drive-train / single gear or tyre friction and this is for a flat road with nil wind.

At 40 mph the i3 consumes a minimum of 3.33 BHP (2.5kW) in drag alone. Not a lot! But accelerate to 60 mph and it goes up a factor of 4 to 12.5BHP (9.317kW). Get on the freeway in Montana or de-restricted Autobahn and at 93 mph the i3 requires 42.14 BHP (31.44 kW)!

It is no wonder that i3 test drivers have noticed a massive reduction in range when driving on faster roads. If you add in tyre resistance, wheel well turbulence, and a less than optimal gear ratio (optimised for acceleration rather than cruising then expect about 60 mile range from a BEV and a bit less all electric from the REX).

What if BMW had optimised just the Aero side?

40mph:

A2: 2.54 BHP(1.894kW),

XL1: 1.30 BHP(2.54kW)

60mph:

A2: 9.52 BHP (7.10kW)

XL1: 4.88 BHP (3.64kW)

93 mph:

A2: 32.1 BHP (24kW)

XL1: 16.5 BHP (12.28kW)

The i3 could be improved by careful modification of the front profile (which could include improvements to pedestrian safety), an extension or redesign of the tailgate and a longer rear spoiler, vortex generators at the rear (perhaps incorporating the trademark aerial) and more ducting air dam style under the car to improve wake and add almost drag free down-force. The door alignment and rear wheel arches could be improved to lessen drag.

Noise:

The i3 internal SPL is actually about 2dBA louder at 50 mph than the diesel Audi A2 due to wind noise. But at lower speeds the ICE can't compete (except with Start Stop at the lights!).

Driver Technology:

The BMW i brand is all about connectivity and city mobility. This test drive did not spend much time in the City. It is not possible to test the iphone/Android app without making a purchase as it is linked to the vehicle's VIN number. I was able to link my phone via Blue Tooth and play music through the radio functions. This worked 90% of the time. Both cars had standard audio which is of reasonable quality. The other 10% there was electronic signal distortion.

The layered menus were not as intuitive as a touch screen app. The iDrive handwriting recognition didn't work for me as a Right handed scribe in a RH Drive car ! My other cars are LHD!

The start up procedure could be simplified. It's not a get away car! Unlike the A2 that tells you to put your for on the brake pedal before start, the i3 makes that assumption. The electronic handbrake took some getting used to but when trusted it seemed to work OK even on hill starts. NB the CFRP Alfa Romeo 4C has a traditional handbrake and is the lightest car in it's class.

Unlike other EV manufacturers the battery regen mode is all about the accelerator pedal. The sweet spot for freewheeling downhill is hard to find with the small text on the Tacho indicating minimal kWh/100km use. This could be corrected with a Head Up Display or peripheral coloured lights to aid the driver to drive more efficiently. Similar displays tell pilots about optimum wing angle of attack in flight.

The white i3 BEV had all the goodies in terms of rear view camera and automatic parking. This worked well 4 times out of 5. The 5^th was the same spot as the 4^th but for whatever reason the car refused to park itself once it found the spot. One issue is the position of the camera which is right on the rear bumper (fender) where it gets covered in road muck. A better spot might be behind the rear glass within the wiper's swept zone.

The large centre screen was a delight if a little distracting on the move. It is especially good in the rear view camera mode (with a clean camera!). But you must still scan between screen and real world to avoid pedestrians who can't hear the i3!

There is no SOC on the BEV which is a shame. The REX has it hidden away on a “hold state of charge” menu.

The vehicle pre-conditioning menu takes some finding but worked on both BEV and REX. It's important to realise the extra electricity you will use to get the car up to temperature in winter. I set 16 deg C for an 0715z departure time on both cars. The mistake with the BEV came when I tried to charge at work using a 13A socket. The car did not charge because the menu had a timer setting (for cheaper home night tariffs). In the end I managed to cancel that and got just an hour's worth of charge.

Breakdown cover:

The i3 has no jack, no spare wheel, no wheel brace. Back in 2003 I learnt the hard way that tyre gunk doesn't work as advertised. In fact I had bought a full set of winter wheels and tyres for the A2 but had left these at home on the daily commute. One of the skinny Bridgestone B381 Eco tyres gave up the ghost at 60 mph. There was no drama and no wheel damage but it was a busy road . Had I had a spare I could have used the underfloor tool kit and Alloy jack to get back on the road within 20 minutes. Instead it took over 4 hours to get a recovery truck out and go home to change wheels.

The i3 cannot be towed in the conventional fashion and must be lifted onto a low loader! I would rather carry a spare. But 19 or 20” in that small boot (trunk)?!

In Germany a full set of Winter 19” rims can be had for 900 Euros. In the UK BMW are charging almost double! LED lights: The BEV had the optional LED headlamps for normal (dipped) use. This gave a pleasant blue / white light. The adaptability was not noticed on country lanes. Main beam was still halogen and no better than other vehicles. The mix of blue and yellow light is a little odd.

How does it drive?

Short answer: Very well!

In fact it is great fun to drive and the novelty of silent startup and acceleration to 40+ mph is superbly smooth. The downside of fun is the temptation to use the available torque. Only once did my free hand reach for a non existent gear stick! Yes I would have liked a second cog for more efficient highway motoring.

The bar graph (approx SOC indicator) goes down like fuel gauge in an English Electic Lightning!

http://www.youtube.com/watch?v=g5dvT-G7JNs

For a newcomer to EVs it feels very odd to start moving in near silence. This requires even greater lookout and anticipation than normal in built up areas as pedestrians do not hear you coming. That is a positive aspect that should re-energise driver skills.

The acceleration is excellent – the REX was not noticeably more sluggish than the BEV. I spent most of the time in ECO PRO mode (with a maximum of 70 mph set for motorways). ECO PRO + was used to get from work to the dealer in Lincoln with a depleted battery. The car felt much more fidgety on the twisty B roads than in Comfort or EP. Perhaps the stability electronics and throttle/extra regenerative braking response has this effect.

Visibility from the driver's seat was better than expected and very similar to the A2. The driver just has to move their head around the thick A pillars when approaching junctions. The grip from the 155 front and 175 rear standard tyres is more than adequate for dry road cornering at speed. The rear tyres did struggle when there was a little mud on the tarmac and the traction control flashed on these occasions. Winter tyres offer a good 3 times the grip and much shorter stopping distances so it would be interesting to compare in winter conditions.

I was surprised that the BEV had 175 section rears and this may have added drag to match the REX. Apparently the REX has a slightly narrower rear track. Steering feel was good even if not direct (servo assisted). Narrow tyres bring steering benefits and

the turning circle impressed all who witnessed it. The cruise control was very good. Neither car had the lane keeping/auto braking technology.

Conclusions:

First off BMW deserves credit for bringing the i3 to market. It offers an alternative approach to EV design and manufacture. The blue sky thinking maybe went a little overboard in the style over substance department.

However, the looks grew on me. Even the cheap looking interior panels! The car drove far better than a car of this mass deserves. In practical terms it is not as good as it could be. BMW could learn a lot more from a similarly sized car built with practicality, ECO credentials, lightness and aerodynamic efficiency that is 15 years older. The aluminium Audi A2 (especially the 1.2 model). One thing they did far better than Audi was in marketing the i3 more aggressively like Toyota did with the Prius.

Improvments: If I were responsible for product development on the i3, for 2015 I'd introduce tat least some of the following:

1. Three door version like Coupe concept

2. Aero optimisation

3. Further weight reduction programme.

4. HUD option with SOC indication

5. More obvious ECO / Freewheel indication

6. More colour choice not linked to interiors

7. Lightweight Biodiesel or CNG REX options

8. More practical 5 door version with B pillar, removable rear seats and FWD to improve rear load space and traction in snow.

9. Better seat raising design.

10. Full LED lighting

11. RH iDrive for RHD and LH iDrive for LHD markets

12. Fairer winter wheel/tyre pricing

13. Better rear camera positioning

14. ICE FWD option without EV for long distance commuters in countries without decent electrical network.

15. Spare wheel/ jack options as alternative to tyre gunk.

16. Better Driver info menus

17. Better English translation of manual

18. Work with Solar PV controller manufacturers to offer old i3 batteries as storage and the likes of “Immersun” to offer Solar PV charging.

19. Encourage Fast DC network expansion in all markets – like FastNED.

Special thanks to Lucas for the in depth review!

aerodynamics B-pillar battery BMW BMW i3 Cd CdA drag coefficient lucas range range extender REx Tires weight wheels -

5 ( 88 ratings )

- Saturday, March 01, 2014