C&D: Drag Queens: Five slippery cars enter a wind tunnel; one slinks out a winner

The EPA has roll-down data for the gas and diesel powered cars but I've not found similar data for the Leaf or Tesla. Still, we can compare the power required for three of the cars listed in the article:
(NOTE: I am working on the table rendering tags)

	performance	Volt	Volt (EPA)	CLA250	CLA250 (EPA)	Prius	Prius (EPA)
1	HP @70 mph	16	21	16	21	14	16
2	HP @100 mph	45	55	48	54	42	45

Sources: ibid and EPA roll-down metrics

• The article reported just aero power
• The EPA coefficients includes rolling as well as aero drag power
• I have not found EPA roll-down coefficients for electric vehicles, yet

I'm seeing good agreement on the Prius:

• 70 mph ~12%
• 100 mph ~6%

But the Volt and Mercedes data is off:

• 70 mph ~24% and ~24%
• 100 mph ~18% and ~11%

The error between the total power from the EPA roll-down coefficients decreases as the speed increases. This suggests we are seeing similar effects of aerodynamic drag having a higher proportion. But the surprise is the 70 mph errors where transmission and rolling drag begin to predominate.

I have an SAE paper that claims the Prius transmission becomes inefficient at higher power levels but I could never find this in my mph vs MPG tests. So here was another set of data showing the Prius transmission and rolling drag are exceptionally well performing. The Mercedes is next. The Volt has an opportunity for improvement, Prius, Mercedes, Volt:

• 70 mph ~12%, ~24%, ~24%
• 100 mph ~6%, ~11%, ~18%

Bob Wilson

 

There is a lot of room for improvement if the Prius lost, barely, out to car with a much lower frontal area.
Really shows how the LEAF needs a major reworking. Yes, distinctive is good, however drag impacts range and for an EV that is a major point.

 

His demands are not reasonable, and a bit offensive, but a Toyota marketer is probably looking at the sales numbers and saying, "We barely sell any hybrids in Europe while California and Japan are the top 2 markets. Let's design the Prius G4 to please those guys, and not worry about EU tastes. Instead we'll push the Auris diesel there."

 

The tesla model S has a larger frontal area than the prius: 25.4 square feet versus 23.9 square feet. The prius is a taller car, but it is not as wide.

The prius can definitely lose some height, but width is already tight if you are putting 3 adults astride in the back seat. I wouldn't be suprised if it grew wider.

Tesla model S has a cd of 0.24 versus prius 15" tires cd of 0.26, using the same wind tunnel. Here there are definitely some tricks like radiator shutters, and small shape changs that could perhaps drop it at most 10%. After that we have extraordinary things like skirts and making it a 2+2 that I doubt toyota wants to do.

On the leaf, I would say the market surveys and pundits have spoken. They don't like the looks, and they hurt the aerodynamics. If it is mainly a city car, the aero isn't as important, but I would expect it to be more aero, with less polarizing looks, in the 2017 gen II

 

You missed your calling Bob. Starfleet diplomacy corps needs you.

 

I do not know. In its current configuration the Leaf isn't a good highway car becaue of range, so I'm not convinced that optimizing shape for highway performance is the right direction, assuming that there are tradeoffs involved. My personal approach has been to divide my car fleet into two categories - city and highway. The Leaf is my primary city car, and the Prius is my primary highway car. So while I care deeply about aerodynamic drag with the Prius, it's far less important with the Leaf. Logging average speeds on both cars over the past few months I see the Leaf @ < 30km/h and the Prius at > 60 km/hr.

The best city cars IMO are generally taller and shorter, which is counter to aerodynamic efficiency. If we're trying to come up with a single multipurpose design we make compromises. But I'd argue that today's mainstream EVs like the Leaf are not by definition mutipurpose designs - their drivetrain is optimal for city use and not really the best solution for highway travel, so why not optimize the body to suit?

I know that in many large US cities people are travelling at highway speeds to get across town, but for the rest of the world that's not typical. In my case when I'm in the city I'm driving slowly, almost always < 80 km/hr and when I leave the city I'm on a highway for a couple of hours, and there's not much crossover.

So for my highway car I want super aerodynamics, and can live with the compromises needed to achieve that, like tortured entry/exit, reduced turning circle, lower seating position, etc. But for my city car give me tall and boxy so I can hop in and out and get my groceries home easily. The Leaf in its current configuration works well in that role.

 

Mitsubishi i-MiEV is an ideal city car. Cheap too (~$15,500 after government subsidy)

 

seems like bassakwards reasoning, for a teeny tiny portion of the population. You are saying that instead of just swapping cars occasionally with a different household member, each person with a bev should also have an aerodynamic high highway mpg car. Most people buy at most 1 regular car for an individual, or maybe a car and a truck or SUV.

I have a memo for you from market research. The Japanese group think idea that the most popular BEVs would be city cars is wrong. If it was correct things like the imev and smart ed would be selling much better. The bigger highway capable leaf and Tesla S do much better in sales than these city cars despite their higher price. Which brings us to polls and market research for the next generation leaf. People do want longer range and to drive it on the highway. People don't seem to be buying because they like the looks. The looks were done at the expense of aerodynamics. That seems to point to improving the aero and battery pack size in the next generation, not pretending that that METI research was correct. We have better facts. Both BMW and Nissan seem to be talking about 300 km range (186 mi), which is probably on an easier test like nedc. Would you like your leaf better if it was say $3000 more but got 150 mpg EPA and had more L3 chargers? I think that is probably a good goal versus assuming these cars aren't driving on the highway.

I definitely understand that when the car was designed, nissan expected much higher sales for japan, and much higher percentages would go to people who only drove in a congested city. In japan this honor goes to the aqua (prius c) and kei cars.

You do relize taht most people don't have 2 similarly sized hatchbacks for themselves.

Wow. Do you think the prius liftback has tortured entry/exit and a bad turning circle? Do you think the Tesla S has these problems. Perhaps you think every one is old and inflexable. Both the Tesla S and prius liftback, you know the 2 cars sold today with the best aerodynamics are easy to get into and out of.

 

Slippery Slope: Production Cars Making Jaw-Dropping Aerodynamic Gains | Vehicles &amp; Technology content from WardsAuto

This answers the question on the cla.

The CLA achieves much of its slipperiness like most new vehicles: Designers carefully manage how air streams around the car’s A-pillars and side mirrors, and how it flows through the engine compartment and around the wheels. Special underbody panels allow air to pass more freely underneath.

However, the CLA180 BlueEfficiency model achieves a world-leading 0.22 Cd with an additional list of features, including a sport chassis and suspension for a lower ride height; smaller 15-in. wheels made of a light alloy and designed to be highly aerodynamic; a radiator partially covered by a blind for active regulation of cooling air and additionalbelly pan and under floor treatments.

These efforts are topped off by a special rear bumper that hides the exhaust pipes and plays a significant role in lowering aerodynamic drag, a Mercedes spokesman says.

The BlueEfficiency version will be sold only in Europe. CLA models available in the U.S. will have less-spectacular, but still impressive, Cds of 0.28 and 0.29, a Mercedes spokesman says.​

Seems a shame that the US doesn't get the euro goodies on the small mercedes. I wonder how much they add in cost.

The vehicle underbody is responsible for about 30% of overall aerodynamic drag and the engine compartment cooling system another 10%, says Toyota’s Young. More underbody sheathing will continue to yield benefits in the future, plus under floor panels offer the additional benefits of reducing road noise and increasing high-speed driving stability.

So-called “cooling drag” will be reduced by the swiftly growing adoption of grille shutters and other technologies related to the engine compartment.​

I wonder how much toyota can reduce drag in the underbody of the prius. At least visually they look like they did a good job on my gen III.

 

The bottom of the Tesla is perfectly flat, and close to the ideal (a waterdrop taper at the end).
So why does Europe always get more models/options than the US? America is supposedly a car-based society (while the EU is train & metro-based), so I would expect us to get more cars to choose from.

 

Straw man, but I'll say that most of the answer to the more efficient car choices are fuel cost.

 

The US gets fewer cars because of safety and pollution regulation. Some see some of these regulations as protectionist. Some see them as protecting citizens. I'll let you choose how to interpret that. On the mercedes cla though none of the regulatory hurdles are impeding american sales, so it may be simply because mercedes doesn't think it will do that much better than the normal cla on the epa test to justify a higher price. I'm sure the diesel isn't going to be sold in the US at first because of the cost of complying with air pollution standards in the US, and the lower sales it expects for diesel.

American's do own fewer cars than the western europeans or japanese though. Go to europe or japan and see all the cars. They have better public transportation but still tons of cars.
It's Official: Western Europeans Have More Cars Per Person Than Americans - Max Fisher - The Atlantic
Then again, the data may be bad. Bottom line is western europe and Japan buy lots of cars. Japan destroys the old ones, europe has an old fleet. If you are a big japanese auto, you can make money in japan, the government subsidizes big auto. Its very hard to make money in Europe. In the US its easy to make money if the car sells in high volumes or is expensive.

 

No. I should have been clearer. I'm in a household with several drivers, and we swap cars, exactly as you suggest. Change 'I' to 'we'.

We always seem to be talking about the future. I understand that, but want to focus on the present.

In my household we have no need of more range from our Leaf in its current role, and honestly if I were in a single car household I wouldn't consider an EV even if it had four times the range, because I want to be able to hop in my car and cover lots of highway miles with no fuss. I'm not sure whether I would have opted for a more expensive bigger battery had it been available when I bought my car. Having a 2x bigger battery would not change the way we currently use the car in any way.

I think that today's EVs are not multi-purpose cars with the possible exception of the Model S. Sure you can drive a Tesla across the country, but you've got to really want to do it, because it's at best very inconvenient. The mainstream Evs in today's world like the Leaf are very well suited to city use, where there are short trips, stop and go driving, and frequent 'refueling' opportunities. So it doesn't seem bassackward to play to those strengths. Many of the disappointed EV owners are trying to do everything with the cars and failing at it. That doesn't mean the car is useless or deficient, it means it's a specialized vehicle not being put to its best use.

No, but lots of households have a mix of vehicles - a fuel efficient commuter, a minivan, a big-nice person 4x4. I'm suggesting that many households can successfully add an EV to that mix, and that for those that do highway performance/economy is probably not going to be at the top of the set of requirements for the EV, because they're going to be driving the EV locally.

Well, I can only speak for myself, and I am old and inflexible Also big. Let's leave the Model S out of this and talk about the everyman cars. The Prius liftback is not particularly easy to get in and out of for me. The Leaf is 2.3" higher, and is easier to get in and out of than the Prius, at least in the front. It was one of the first things I checked when considering the car. Reducing the height of the Leaf to gain aerodynamic efficiency would for me be a negative feature. The Prius is a multi-purpose design that could most certainly be further optimized fo aerodymamic efficiency, but it would likely come at a cost. I don't think that anyone can deny that there are a set of tradeoffs, and I stand by my claim that in many cases design features that make a car more aerodynamic make it less suitable as a city car. Of course all cars should have louvred air intakes, LRR tires, covered underbodies and things like that, but beyond those features it's largely optimizing for a particular set of requirements, and you give typically give up one feature to get another.

 

Good then we are on the same page. And fortunately or unforturnately you do fit the leaf demographic

Not much we can do about the past I think nissan is trying very hard to figure out how many would opt for a bigger battery, and how many would simply buy something else if they didn't have the choice of short range batery. Now even if you design it for 2 different battery sizes , you need to design of the longer range, and that would likely include better aero.

When tesla, volt, and leaf drivers have been polled they overwhelmingly like their cars.

The tesla does show that a lot of those japanese assumptions on what bevs can't do, are false.

 

Geez do you have twist everything? Look, we burn gobs of gas and energy here in the US. In my opinion, Prius liftback sales have been ok since 2009, but not great. Don't you want to see Prius consistently sell in top 10 in US? Japan and US are by far the biggest markets for Prius.

 

It isn't like different car models and designs aren't already targeted at different markets. Look at how few fastbacks are sold in the US where the sedan version sells. Their fastback models are reserved for countries where they sell. No point in having cars stack up on dealer's lots. That wastes the energy used to create them.

 

It takes 30 minutes to refuel a Tesla EV every three hours... what's inconvenient about that?

No not a strawman. (And not just confined to small cars.) Let's take a VW passat. Here we get 3 choices: Gasoline, gasoline with turbo, or the diesel. In the EU they can have a gasoline engine as small as 1.4 liter (three cylinders) or as big as 3.0. Diesel choices also range from 1.4 upto 3.0 if I recall correctly. They have about 10 different choices for powerplant vs. our three.

Ditto with other cars. We talk about the "new" Ford Fiesta with 1.0 engine, but Europe has had that engine for years. (They also have it available in the Focus and Fusion.) Honda sells Civics in the US, but in Europe they have the hatchback.... we don't have option in the US. We also don't have the diesel Civic which Honda introduced almost ten years ago.

For a long time, Beetle afficionados have wanted the VR6 engine. In Europe it's available. In America: No we don't get it. Too bad for the yankee doodles.

Also: The 70mpg Honda Insight is NOT the high MPG king. That honor belongs to the VW Lupo at 88 highway mpg. And no it wasn't available in the US..... only Europe because that continent gets more models/options in car than we do.

Toyota sells diesel sedans/hatchbacks in Europe. We americans get no diesels. Toyota has about 6 different gasoline engines you can stick inside a Corolla. We get two. Plus the company sells a Prius with seven seats. Americans have large 6 or 7 member families, which is why minivans and sport-utes are so popular. The Prius with 7 ought to be sold here, but we don't get it.

The BMW 535d is a nice new car.
We get ONE version of it.
Europe gets four (including gas version).

I could go on-and-on but it's late and I want to go to bed. But I will repeat what I said: "Why does Europe always get more models/options than the US? America is supposedly a car-based society (while the EU is train & metro-based), so I would expect us to get more cars to choose from."

troy

 

I disagree.
I am currently on a vacation. We started in Minnesota, drove out to California and are currently on our way back.
The scenery has been phenomenal! I have never enjoyed a vacation as much as this.
We have had a mix of scheduled destinations and events and random stops when we felt like it (I highly recommend southeast Utah for some really cool sites).
Charging has been incredibly convenient and fuel cost is zero

Aside from that, the Model S are our only vehicles and we use them for all of our driving needs.

I don't doubt that an EV only garage would not work for you. Please don't assume it won't work well for others.

 

I am curious to see what Cd the Model S in standard height or with standard suspension would do...also wonder how the different 19's available vs. 21's would make any difference? The 19" Aero wheels looked to be promising but were discontinued due to low demand and TBH, the ruined the sexiness of the car for the benefit of aerodynamics.

 

Well I think the aero wheels look nicer than the turbine fan wheels. Also the base pricetag on the S-85 was $4000 lower.