One point of contention in discussions of electric cars is range. Many people might not buy an EV that has just a hundred miles of range. Others might be holding on for an affordable EV to get the same range that they could get from an ICE vehicle. Some may think that the future depends on batteries with a lot of energy density, but there’s another way.
Our friend and leader David Tracy is clearly very excited about his BMW i3 purchase. If I’m honest, I’m quite jealous about it, too! I fell in love with the i3 back at the 2014 Chicago Auto Show and the funky BMW has been on my bucket list ever since. I mean, it’s a pretty wicked little car. When new, that i3 gave its owner roughly 75 miles of range. Then when the battery gets depleted, a little Kymco 647cc parallel twin fires up and keeps the electrons flowing enough to give you another 70 miles. Then you can just fill up and get another 70 miles. And by the way, that engine was used in the BMW C650 GT scooter.
David mentions “Vehicle Demand Energy” in his piece, and he explains that BMW designed the i3 to be lightweight and aerodynamic so that it can squeeze every little bit of range it can out of that battery.
For today’s COTD, we don’t have the usual funny business, but something informative. Toecutter, one of our awesome engineering readers, elaborates on how EVs with small batteries can have decent range:
We already have the technology to get long range with tiny batteries. It’s called load reduction.
Consider the BMW i3’s energy consumption. It uses 0.27 kWh/mile. It has a mass of 1,345 kg and has a drag coefficient of 0.29 with a frontal area of roughly 2.3 m^2. Not too bad as far as electric cars go.
But the Tesla Model S PLAID beats it at 0.24 kWh/mile WHILE it weighs almost twice as much, at 2,237 kg. This is because its drag is significantly lower, with a Cd value of 0.20 and a frontal area of roughly 2.3 m^2. You can nearly double the mass, but by cutting the drag by 1/3, you’ll still see a reduction in energy consumption in mixed use, most of that from improved efficiency on the highway.
And it is on the highway, not in the city, where range is most important, because most people who own an EV can plug it in each night and start with a full charge, and most people who drive hundreds of miles in a day, primarily do so on the highway.
Taking this a step further, consider the GM EV1. It has a mass of roughly 1,320 kg, a Cd value of 0.19, and a frontal area of roughly 1.9 m^2. It only needed 0.15 kWh/mile. Almost half that of the BMW i3, while weighing a similar amount.
An inexpensive, long-range EV doesn’t need to be a cramped penalty box, either. A long wheelbase sedan will work just fine. Consider a classic Mercedes W126. The frontal area of a 300SD is about 2.2 m^2, and this is a tank of a car with plenty of headroom. Build it with conventional materials, and it is conceivable that with a small 30 kWh pack, it could weigh in around 3,500 lbs complete while passing all NHTSA regulations. Then consider super-streamlined cars like the Solectria Sunrise with a 0.17 Cd, GM Precept with a 0.16 Cd, or Ford Probe V with a 0.137 Cd. A 0.15 Cd value is certainly achievable for a usable and practical road-going car, and the publication “Aerodynamics of Road Vehicles” by Wolf-Heinrich Hucho said as much nearly 40 years ago.
What you end up with if you design to the above described specs is a comfortable vehicle that offers plenty of passenger space, that can seat 5-6 adults, have enough trunk space to fit 15 dead hookers chopped up(albeit the car would go over GVWR if you did that), and only needs somewhere around 0.13 kWh/mile to maintain 70 mph on the highway. In turn, that 30 kWh battery pack would deliver more than 200 miles range consistently, perhaps down to 150 miles in the worst of winter(still decent), and cost comparatively little to build. Use LiFePO4 chemistry, and now you don’t have to worry about it catching fire. If you opt to use a single series string of large AH prismatic cells of the LiFePO4 chemistry, you avoid the need for a BMS as well(bottom balance it to within 0.001v of each battery before pack assembly, and it will stay that way for decades), or at the very least, can keep the BMS very simple and non-integrated into the rest of the car’s electronics. Build the car with actual physical buttons, avoid all the integrated electronics modern cars are known for and opt for dumb, simple terminal blocks for connections in accessible places using thick corrosion-resistant wires much larger than the current draw requires them to be, and maybe revert the design back to the OBD-II standard, and now you have a car that is fully repairable by a hobbyist mechanic with basic tools, and with very little to go wrong. Want infotainment? Have a display screen that outputs whatever you want it to from your phone, but otherwise leave the car without a proprietary touchscreen controlling everything. For backup camera, a cheap non-proprietary system replaceable with a $20 AutoZone or O’Reillys version if it breaks will suffice.
Now you have a family hauler built to last a lifetime that doesn’t need a massive, expensive battery pack, and for which everything in the car is cheap to fix.
It gets even better when you consider sports cars. Something sized like a Lotus 11, but streamlined to a Cd value of ~0.15, with a mass of around 800 kg, would only need around 0.080 kWh/mile to maintain 70 mph on the highway. A 25 kWh pack would be plenty for such a thing, and if it had 300 horses like a Tesla Model 3, it would have enough power to accelerate like and top out like a modern hypercar, without the hypercar pricetag or hypercar maintenance costs, while being light and nimble enough to out-corner and out-maneuver a hypercar. With the complicated build techniques and material choices of the i3, it would be able to pass regulations, and the price point could target at or below Alfa Romeo 4C or Lotus Elise money.
If that’s too long, I’ll keep it short and simple: An automaker could achieve awesome range with current battery technology by making their vehicles slip through the air. David and Toecutter aren’t just pulling it out of their respective tailpipes, either. Even e-motec, a magazine covering the technical side of this industry, says that over 50 percent of energy is spent on just pushing air away, so good aero helps.
Have a great evening everyone!
The Ioniq 6 is definitely a solid step in that direction. Same battery as the other eGMP platform cars, but significantly better range.
I’d love to see someone take another crack at the Commuter Cars Tango concept. It had (technically has, I guess, in theory you can still buy one) decent performance numbers even for a modern EV and a version made with more modern tech probably has a better chance at success than Aptera.
I’d want it to be lower and longer, like the VW 1-Litre concept. Retain the tandem two-seater layout. You could end up with an EV that has a 10 kWh pack and gets a 500 mile range at highway speeds using it, and because the battery is so small, can be charged from 0-80% at a fast charge station in a bit over 5 minutes(assuming an appropriate battery was selected. The LoneStar batteries could do it, and an appropriately sized pack of such would be capable of 1,000 horses peak). The car itself, empty could weigh in around 400 lbs. With AWD hub motors making about 200 horsepower, performance would be more than a bit crazy.
Speaking of aero, I still have an article about drag locked and loaded for you guys.
Looking forward to it.
I don’t know if everyone here appreciates that while mechanical resistance and rolling resistance scale linearly with speed, aerodynamic resistance scales with the *square* of speed. I think that needs to be emphasized in this discussion.
For a car like the i3, which (I think) was conceived mostly as an urban runabout, it’s not as big a deal if your effective top speed is ~35 mph (although that’s not to say it’s not important), but when you’re shoving air out of the way at 70 mph, it is a very big deal.
“Something sized like a Lotus 11…”
Maybe even a Lotus 23. IIRC, FIA regulations at the time required a seat for a passenger, a spare tire, and a “trunk” large enough to hold a suitcase of specified dimensions, so one could make a (weak) argument that it was practical.
It will never happen, but it does give an old man something to dream about.
With an EV having the batteries built into the floor of the car, options for placing storage space increase greatly. Both a frunk and a trunk would be possible in such a small, narrow car without the need to accommodate an ICE and everything that comes with it.
Am I the only one concerned about people that measure cargo size in dead hookers?
I’m just glad someone caught the joke.
When I saw the headline I thought “That’s it, The Autopian is finally going to talk about the Aptera and its 400miles of range with 40kwh battery !” Maybe next time…
This is a still good article though.
We have to stop this arms race to bigger and bigger batteries.
The range is one thing, but the materials to build the battery and the energy to charge it have to come from somewhere…
In my state, a “Zero-emissions” EV is actually a 47% gas and 20% coal vehicle…
Drag coefficient of .013 FTW.
Off by a decimal place, but 0.13 is very slippery. Especially since the car has outboard wheels, which means the exposed axles and streamlined wheel fairings are MOST of the Aptera’s drag. Potential exists to get even more slippery. My Milan SL velomobile has a Cd value of 0.08, although in order to do this, its ground clearance is only 3 inches and the front wheels are restricted, greatly increasing turning radius. If you don’t give a crap about looks, a usable road going car can still approach 0.11.
0.13 is the same value as the 1967 Panhard CD Peugeot 66C LeMans race car, designed by Charles Deutsch and Rene Bonnet, which tried to squeeze as much top speed as it could out of a 4-cylinder 1149cc Peugeot 204 engine. A mere 108 horsepower got it to 160 mph on the Mulsanne Straight. It also helped that the car only weighed 1,650 lbs. Imagine a modern sports car with this sort of low mass and aero slipperiness, powered by an engine from a Civic SI. You’d have an 80+ mpg sports car(at least on the freeway) that could hold its own with a hypercar.
I feel like front wheel restriction could be removed entirely if you built a vent system that utilized the venturi effect to create an air curtain to deflect the air around the wheels.
Luigi Colani did this with some of his car designs.
In the case of the Milan velomobile I own, this technique could not be used because the heel bumps required to make clearance for one’s feet while pedaling get in the way of the underbody airflow, thus they are streamlined to minimize drag. In order to use this effect in my custom microcar, I’d have to eliminate the pedal drivetrain, or alternatively, have my feet positioned higher up which would require a large windscreen area so I could see ahead of me, which would cause me to bake in the summer heat.
Cars are actually simpler to design in some ways than human powered vehicles.
Basically an electrified Honda Insight Gen 1, if I can get 62mpg on average and its not because of the battery sitting in the back that actually the only job is to assist during acceleration and shutting the engine off when you almost stop, the battery cannot handle acceleration on its own. Anyway, with a small battery (25kWh) I bet you get a decent amount of range. If this is not a solution, K-Swap will be lol
K-swapped Insights are lovely. Honda should have made the car rear-drive with this engine, from the factory. It would hve punched well above its weight at cars three times the cost, while still getting higher fuel economy than anything you could buy. There is a gentleman on Ecomodder who built a K-swapped Insight, and with mostly city driving, he still averaged more than 45 mpg. 0-60 mph time was about 5 seconds, traction limited because of front wheel drive. With the Insights aerodynamics, if one were to tune such an engine to about 300 horsepower(allowing it to still be very reliable and last 250k+ miles), 200 mph would be in reach with optimized gearing.
I agree, however arguably the most aerodynamic cars are the largest and least useful cars.
The most practical shape for an automobile to be in order to haul the most people and the most stuff is a box. COE or cab forward designs result in the shortest OAL with the shortest overhangs. However it literally has the aerodynamics of a brick
One of my favorite car designs is the Scion iQ, seating for 4 in a car nearly as small as a smart car with nearly as good of a turning circle while being FWD. However it is far from aerodynamic, and with crud like the Footprint rule actively penalizing it for being too small it is highly unlikely to come back to the US as it isn’t efficient, and for both hybrid and BEVs it is lacking a lot of necessary space for those drivetrains.
A 4 seat car built to be twice as aerodynamic as the iQ is almost certainly going to be twice as long, have a much wider turning circle, and much less usable storage space.
Personally I only need 3 seats in an automobile of mine, and using a central driving position with 2 seats staggered behind the drivers seat like on the Ferrari 365 P Berlinetta Speciale and the McLaren F1 would allow you to improve aerodynamics a good deal while having one standard interior layout for all markets due to the central driving position.
I’m sorry guys but 2 seats is just 1 too few for me.
Actually, one fore two aft is not the ideal aerodynamic shape – two fore, one aft is. A teardrop/raindrop shape is the ideal macroaerodynamic form in Earth’s atmosphere.
I say macroaerodynamic because the shape might be able to be improved slightly on a micro-scale using material shapes based on sharkskin.
Fair enough. I am still a big fan of the central driving position though
…Until you pull up to the drive-through ATM.
Teardrop yes. Raindrops (freefalling) are more spherical/hamburger bun/parachute shaped.
But cars are not as pliable as raindrops, so teardrop it is (or penguin shaped?)
Fair enough. Either way, a teardrop shape is essentially ideal for subsonic aerodynamics where the Reynolds number is above one.
Another way to look at it is a wing profile that generates no lift is the ideal two-dimensional shape for aerodynamics in subsonic movement, and if you take that profile and turn it in three dimensions, you end up with a teardrop.
Check out the Volvo 3CC concept. It has a seating arrangement like you describe.
Really Cool! Thanks!
I was going to say check out Aptera
Smaller tires would also help. The i3 should’ve used a size like 155/80-13 or 175/70-13 something
How much difference would smaller diameter wheel make?
Minor, maybe not even a single percentage point, overall, but most of the impact would be at lower speed stop and go driving. Smaller diameter wheels would mean less mass to spin up to speed and thus inertia losses incurred during acceleration and less energy wasted when braking.
This is a fucking superb comment/article.
Round of applause gif for Toecutter.
The first part of TC’s comments are always great, but then he gets into the weeds with stuff that will never, ever happen. Manufacturers don’t want hobbyist-repairable cars. They don’t want them to last a lifetime. They don’t want to spend the money on buttons and switches. They want maximum profit, as all modern capitalism does, and all of those reduce it in both the short- and long-term.
This is stuff that needs to happen. Infinite growth on a planet of finite natural resources is not possible. Continue on the current course, and Karl Marx’s predictions for the end stage of industrial capitalism will inevitably come to fruition, because we can’t keep increasing resource consumption forever, indefinitely. Address this early enough, and there’s no reason we should ever have to give up sports cars, musclecars, or V8s in order to save the planet. Wait too long, and cars won’t be viable at all to anyone except the financial elites(and that’s probably the world these financial elites want anyhow). I guess profits are always more important though… they always are to guys in suits, who won’t have to ever deal with the consequences of their actions.
I remember when Mercedes-Benz used to build cars that if you took care of them, could last 500,000+ miles, and could be repaired mostly with basic tools, and as long as you could source parts, when repaired could be made as good as new. Those days are long passed, to the detriment of everyone who owns one made after.
Needs to be, but absolutely never will be. Hell, you could try to make your own car and sell it, but you’d never even get the funding to start production – investors would never see an ROI.
Capitalism is a disease, but at this point, it’s terminal.
Agreed, basically we just need modern, GM EV-1 or Honda Insight-shaped electric cars to achieve good range with less battery weight/capacity.
Sounds great on paper, at least it did, before sedans died out.
In real life, we mostly want SUVs and trucks, that are the opposite of good aerodynamics.
Unless battery tech improves significantly, this will always be a compromise.
People like SUVs because you sit high, which makes it easy to get in and out of and the height, high window line and general chunkiness makes them feel safe.
Manufacturers like them because they’re easier to pass pedestrian impact regs, sell for a premium over same sized hatches and for evs, allow for easy/lazy packaging of a big block of battery under the floor.
I think a move the low drag vehicles is coming, see the Mercedes EQXx concept, excitement for the Aptera, but at the moment range is marketed in battery capacity.
It also needs a culture change, consumption is seen as good, particularly in large areas of the US, which is just dumb. Efficiency is the future.
The EQXX concept gets efficiency figures as I describe in my post. It’s a car that can comfortably seat 5 adults, and gets 6 miles per kWh. It is also heavy, lugging around a massive battery pack to get range comparable to Mercedes’ diesel models.
EQXX has a 60(ish) KWH battery, so smaller than a Tesla Model 3 or Y & even though the better aero gives it a much better range (than even the long range Tesla model S or Lucid Air long range, you are right it still is said to weigh 3900 lbs. Even though it is a prototype & designed by mercedes f1 engineers.
Also, (Unfortunately) the car that arguably inspired the eqxx (Lightyear’s Zero which became the Lightyear One) if any are produced, are $250k and Lightyear is in the bankruptcy process trying like hell to come back to make the Lightyear Two, which is they are saying should be priced below $50k.
Oops I was wrong, it looks like the EQXX has a 100 KWH pack