Teardrops and wind tunnels: A look at the world’s most aerodynamic cars

Inspired by VW's ARVW concept, we look at the cars with tiny drag coefficients.

Read the whole story

 

[Jim Z]

"lake" wheel covers used to be a common sight back in the early days of people making speed runs on the Bonneville Salt Flats.

 

[Caffarius]

When I think of funky aerodynamic cars, my mind always immediately jumps to the Mitsubishi HSR-II. It emphasized active aerodynamics and had panels that could vary the drag coefficient from 0.20 to 0.40 with some neat engineering.

 

[yakinabe]

But Cd is only part of aerodynamic drag - drag is actually proportional to CdA (i.e. Cd x A), where A is the frontal area. In other words, minimizing the frontal area is just as important as streamlining the shape.
https://en.wikipedia.org/wiki/Automobil ... #Drag_area

 

[Dr Gitlin]

But Cd is only part of aerodynamic drag - drag is actually proportional to CdA (i.e. Cd x A), where A is the frontal area. In other words, minimizing the frontal area is just as important as streamlining the shape.
https://en.wikipedia.org/wiki/Automobil ... #Drag_area

You know how I can tell you didn't finish reading this article?

 

[Gabara]

All this talk about drag....

 

[yakinabe]

But Cd is only part of aerodynamic drag - drag is actually proportional to CdA (i.e. Cd x A), where A is the frontal area. In other words, minimizing the frontal area is just as important as streamlining the shape.
https://en.wikipedia.org/wiki/Automobil ... #Drag_area

You know how I can tell you didn't finish reading this article?

Huh. In my defense, I did read the entire article, but not the sidebar. I guess I'm used to other web sites where boxes contain ads or pull quotes, not sidebars with useful info.

 

[kukhuvud]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains! I'd imagine that Tesla's designers also have access to tests of Cd?

Edited for clarity.

 

[Fatesrider]

Who knew driving without the right kind of wheel covers could be such a drag...

I'll see myself out...

 

[Jim Z]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

believe me, if Tesla could eke out another 6% with some simple bolt-on devices, they'd be on every car they build. 6% is the kind of gain any car company would spend money to get. the vast majority of the time when any aftermarket bolt on device does make a noticeable difference, it's only in specific situations and often degrades things in other situations.

 

[Dputiger]

What's the net gain in efficiency for Cd improvements? Say the Model 3 went from its current rating down to the 0.045 mentioned in the article and somehow did this without changing anything else about the vehicle, for simplicity's sake.

How much would range improve?

 

[yakinabe]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

The splitter extension probably reduces ground clearance. They claim it only reduces ground clearance by 1/8", but that's probably on a flat surface. A longer "chin" makes it more likely to strike a ramp or driveway.

Not sure about the rear spoiler, but it's a very sharp (thin) edge. May be difficult to manufacture, and/or prone to damage, and possibly a safety issue (e.g. if a cyclist gets "brake checked" by a Tesla driver).

 

[kerbaldroptest]

What's the net gain in efficiency for Cd improvements? Say the Model 3 went from its current rating down to the 0.045 mentioned in the article and somehow did this without changing anything else about the vehicle, for simplicity's sake.

How much would range improve?

Probably would depend wholly on the rolling resistance and losses from braking (with regen, the efficiency of that regen would matter). However I have no idea what proportion is aero losses vs other. Probably significant though!

 

[yticolev]

All of those listed Cd's are suspect as they were all tested in different wind tunnels with different methodology and cannot be peer reviewed in any meaningful way. In addition, virtually manufacturer lists the CdA of there cars. This number at least could be correlated against mpg and HP numbers and speed to determine if the underlying Cd is realistic or not.

Area (the "A" in CdA) is a huge factor in efficiency or top speed. I was struck looking at all these pictures how narrow most of them were.

Edit: I too missed the sidebar.

 

[rosen380]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

The splitter extension probably reduces ground clearance. They claim it only reduces ground clearance by 1/8", but that's probably on a flat surface. A longer "chin" makes it more likely to strike a ramp or driveway.

Not sure about the rear spoiler, but it's a very sharp (thin) edge. May be difficult to manufacture, and/or prone to damage, and possibly a safety issue (e.g. if a cyclist gets "brake checked" by a Tesla driver).

If some bolt on pieces increased efficiency by 6%, but did so by significantly reducing down-force, that could impact performance and handling and such.

Maybe the re-routing of airflow takes cool air away from the batteries and such and would have some long-term consequences?

 

[Dr Gitlin]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

believe me, if Tesla could eke out another 6% with some simple bolt-on devices, they'd be on every car they build. 6% is the kind of gain any car company would spend money to get. the vast majority of the time when any aftermarket bolt on device does make a noticeable difference, it's only in specific situations and often degrades things in other situations.

The link in that section of text goes to some CFD work that company did that shows those new spoilers should cut drag: https://unpluggedperformance.com/aerody ... a-model-3/

Although as both you,, yakinabe, and rosen380 point out, nothing is free, and it might mean an inability to clear parking ramps and speed bumps, plus a dangerously sharp edge on the lip of the rear spoiler.

 

[Rbrian]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

Sometimes it is possible! My company remapped all our vans, and put stickers on the back saying they had 25% less emissions. This seemed unlikely, but having driven thousands of miles before and after, I think it's true. I used to get 350-400 miles from a tank of diesel, now I get 450-500 - 25% more range tracks with 25% less emissions.

It doesn't feel any less powerful, but the power is compressed into a narrower band requiring more careful gear choice (like most European vehicles, it's a stick shift). It didn't take me long to get used to it, and now I'm baffled as to why the manufacturer didn't do it - efficiency sells!

 

[ACorbs]

Why doesn't anyone publish or talk about the second or third term in the drag ce? I mean the first term is linear and has no real world impact above 50 mph. I don't care about drag at low speeds, I want to know what is a real highway sipper and what is not!

 

[Marc J]

Check out the AeroVelo Eta, the speed bike that I worked on in university. It currently holds the human powered speed record - nearly 90 mph just with a buff guy pedaling.

We calculated our miles per gallon equivalent at 9544 MPGe. We never wind tunnel tested it, so not completely sure what the Cd ended up at, but it might be a little better than the TUDelft vehicle mentioned. Definitely better if you look at CdA, because we only have two wheels.

 

[phlip]

But Cd is only part of aerodynamic drag - drag is actually proportional to CdA (i.e. Cd x A), where A is the frontal area. In other words, minimizing the frontal area is just as important as streamlining the shape.
https://en.wikipedia.org/wiki/Automobil ... #Drag_area

CdA ist only part of aerodynamic drag which is actually proportional to CdA x v**2. So overall, minimizing speed is the most important factor.

;-)

 

[Rbrian]

Check out the AeroVelo Eta, the speed bike that I worked on in university. It currently holds the human powered speed record - nearly 90 mph just with a buff guy pedaling.

I once hit 50mph on a Specialized Rockhopper hardtail mountain bike with 2.2" knobbly tyres, powered by nothing but a skinny 16 year old... with a little help from the Earth's gravity. It was a very steep downhill, which is why I chose it. My tyres were squealing round the bends, I wanted to slow down but I was too afraid to brake, so I had to ride it out. I passed two cars!

 

[yankee77wi]

The 1969 Dodge Daytona had a drag coefficient (cd) of just 0.28, better than most cars made in the 1990s. It would have produced even less drag, if it weren't for the tall spoiler (added to keep the rear wheels on the ground at high speeds), but still achieved 200 mph. It didn't run on electric, but was an electrifying design. I'd buy one of these in a modern shell hands down before any of these wannabe designs. Pure muscle!! (no rice)

 

[Me Myself And I1]

Wait, no mention of Tatra 77?

It was the first production car designed with aerodynamics in mind.

And while it's not clear whether 0.212 is the drag coefficient of the car itself or a 1:5 model, Tatra 77/77a and later models were pioneers or teardrop design.

It can be seen in Transatlantic Tunnel movie.

https://en.wikipedia.org/wiki/Tatra_77

Edit: added link

 

[yakinabe]

But Cd is only part of aerodynamic drag - drag is actually proportional to CdA (i.e. Cd x A), where A is the frontal area. In other words, minimizing the frontal area is just as important as streamlining the shape.
https://en.wikipedia.org/wiki/Automobil ... #Drag_area

CdA ist only part of aerodynamic drag which is actually proportional to CdA x v**2. So overall, minimizing speed is the most important factor.

;-)

Yes, very true. That's why the US instituted a 55 mph speed limit in response to the oil crisis.

There's also the ρ (air density) term in there, which is why they go to high altitudes to set land speed records.

 

[Stuart Frasier]

My favorite VW "1-liter-car" was the original concept with tandem seating.

https://www.supercars.net/blog/2002-vol ... e-concept/

 

[Jim Z]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

Sometimes it is possible! My company remapped all our vans, and put stickers on the back saying they had 25% less emissions. This seemed unlikely, but having driven thousands of miles before and after, I think it's true. I used to get 350-400 miles from a tank of diesel, now I get 450-500 - 25% more range tracks with 25% less emissions.

It doesn't feel any less powerful, but the power is compressed into a narrower band requiring more careful gear choice (like most European vehicles, it's a stick shift). It didn't take me long to get used to it, and now I'm baffled as to why the manufacturer didn't do it - efficiency sells!

horseshit. 25% increase in fuel economy with just a reflash? That doesn't even pass the sniff test.

 

[yakinabe]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

Sometimes it is possible! My company remapped all our vans, and put stickers on the back saying they had 25% less emissions. This seemed unlikely, but having driven thousands of miles before and after, I think it's true. I used to get 350-400 miles from a tank of diesel, now I get 450-500 - 25% more range tracks with 25% less emissions.

It doesn't feel any less powerful, but the power is compressed into a narrower band requiring more careful gear choice (like most European vehicles, it's a stick shift). It didn't take me long to get used to it, and now I'm baffled as to why the manufacturer didn't do it - efficiency sells!

Let me guess, they made this change, and told you how to change your driving habits to take best advantage of it. You already mentioned one - change gear shift points. If you'd just taken these advice without modifying the van, you'd have had the same results.

 

[mbmcavoy]

Wait, no mention of Tatra 77?

It was the first production car designed with aerodynamics in mind.

The Rumpler Tropfenwagen was more than a decade earlier, and while it might not have used formal aerodynamic engineering, it was streamlined for low drag, and achieved a Cd of 0.28.

https://en.wikipedia.org/wiki/Rumpler_Tropfenwagen

 

[Dr Gitlin]

Wait, no mention of Tatra 77?

It was the first production car designed with aerodynamics in mind.

And while it's not clear whether 0.212 is the drag coefficient of the car itself or a 1:5 model, Tatra 77/77a and later models were pioneers or teardrop design.

It can be seen in Transatlantic Tunnel movie.

https://en.wikipedia.org/wiki/Tatra_77

Edit: added link

I left it out because of that very complication.

 

[dj__jg]

Wait, no mention of Tatra 77?

It was the first production car designed with aerodynamics in mind.

And while it's not clear whether 0.212 is the drag coefficient of the car itself or a 1:5 model, Tatra 77/77a and later models were pioneers or teardrop design.

It can be seen in Transatlantic Tunnel movie.

https://en.wikipedia.org/wiki/Tatra_77

Edit: added link

I left it out because of that very complication.

I would sooner trust the Tatra number than anything Lightyear ONE claims.

They're constantly making extremely outlandish claims, the stuff they say about their solar-charging roofs is generally impossible with current solar panels and anything other than a giant umbrella-slab of solar panels.

I'm ashamed to share a country with a vapor company like them.

 

[TheCathedral]

But Cd is only part of aerodynamic drag - drag is actually proportional to CdA (i.e. Cd x A), where A is the frontal area. In other words, minimizing the frontal area is just as important as streamlining the shape.
https://en.wikipedia.org/wiki/Automobil ... #Drag_area

You know how I can tell you didn't finish reading this article?

Huh. In my defense, I did read the entire article, but not the sidebar. I guess I'm used to other web sites where boxes contain ads or pull quotes, not sidebars with useful info.

Holy shit, haha. I had to go back and read that too because I'm conditioned the same way. "Wait, what, a sidebar?!"

That's why I support this site.

 

[Tofystedeth]

Check out the AeroVelo Eta, the speed bike that I worked on in university. It currently holds the human powered speed record - nearly 90 mph just with a buff guy pedaling.

I once hit 50mph on a Specialized Rockhopper hardtail mountain bike with 2.2" knobbly tyres, powered by nothing but a skinny 16 year old... with a little help from the Earth's gravity. It was a very steep downhill, which is why I chose it. My tyres were squealing round the bends, I wanted to slow down but I was too afraid to brake, so I had to ride it out. I passed two cars!

The saying about riding a tiger comes to mind.

 

[yticolev]

Check out the AeroVelo Eta, the speed bike that I worked on in university. It currently holds the human powered speed record - nearly 90 mph just with a buff guy pedaling.

I once hit 50mph on a Specialized Rockhopper hardtail mountain bike with 2.2" knobbly tyres, powered by nothing but a skinny 16 year old... with a little help from the Earth's gravity. It was a very steep downhill, which is why I chose it. My tyres were squealing round the bends, I wanted to slow down but I was too afraid to brake, so I had to ride it out. I passed two cars!

That would indeed be scary on knobby tires! My personal terminal speed on a upright bicycle as tested over 50 years or so appears to be 46 mph on road tires, tucking or pedaling. That is not seeking out the longest steepest roads or wearing skin suits and just what I find along the way on normal rides.

 

[TheOldChevy]

I wonder what was the Cd of the Ferrari 512S Modulo. This was my dream car when I was a kid. I suppose that it wasn't so great because the technologies of the 70's were not that advanced, but it really looked aerodynamic and futuristic.
https://fr.wikipedia.org/wiki/Ferrari_Modulo

 

[jerryroane]

TriTrack dual mode guideway EV has a measured wind tunnel Cd of 0.07
That allows high speed on the guideway with low energy. Low energy in turn allows PV solar power to be practical. Half the cost at three times the speed all going back to 0.07 Cd.

 

[cse84]

What's the net gain in efficiency for Cd improvements? Say the Model 3 went from its current rating down to the 0.045 mentioned in the article and somehow did this without changing anything else about the vehicle, for simplicity's sake.

How much would range improve?

A little back of the envelope calculation for the Tesla Model 3: At 80 mph in standard atmosphere, the aerodynamic drag should be on the order of 0.23*1.44*1.85*(80*1.609/3.6)^2*1.29*0.5=505 Newtons. That would fall to 99 Newtons by reducing Cd to 0.045. Rolling resistance, using Wikipedia's value for "Ordinary car tires on concrete" would be in the range 0.01-0.015 times 1611*9.81, so 158-237 Newtons. At low speed, aerodynamic drag would of course be much lower, so the actual range improvement would depend on your typical driving conditions, but might be up to (505+158)/(99+158)=2.58 if you drive 80 mph constantly. Driving in high altitude or high temperature (both reduce air density) would reduce aerodynamic drag and thus also the possible range improvement, but it would still be quite a significant improvement.

Of course you can't expect a Cd reduction without changing the weight or cross-sectional area of the vehicle, so this is pretty academic.

 

[Me Myself And I1]

Wait, no mention of Tatra 77?

It was the first production car designed with aerodynamics in mind.

And while it's not clear whether 0.212 is the drag coefficient of the car itself or a 1:5 model, Tatra 77/77a and later models were pioneers or teardrop design.

It can be seen in Transatlantic Tunnel movie.

https://en.wikipedia.org/wiki/Tatra_77

Edit: added link

I left it out because of that very complication.

Acknowledged. However, I would argue that the car should be on the list for several reasons:

a) it was a production car that pioneered both the aerodynamics and the particular design*
b) very few survived and testing the cd is a problem
c) despite it's meager power, it was quick and stable, which does point to advanced aerodynamics for its era

The 0.212 is probably unrealistic. "Tatra 87 had a drag coefficient of 0.36 as tested in the VW tunnel in 1979 as well as reading of 0.244 for a 1:5 model tested in 1941."

This could perhaps provide a clue.

Perhaps an article on history of aerodynamics in car design might be useful.

*Yes, Rumpler Tropfenwagen...

 

[Me Myself And I1]

Wait, no mention of Tatra 77?

It was the first production car designed with aerodynamics in mind.

The Rumpler Tropfenwagen was more than a decade earlier, and while it might not have used formal aerodynamic engineering, it was streamlined for low drag, and achieved a Cd of 0.28.

https://en.wikipedia.org/wiki/Rumpler_Tropfenwagen

I know. BTW, Herr Rumpler owned a Tatra 77

 

[real mikeb_60]

Honda Insight (gen 1) was a cd wonder when it came out: 0.25 according to Wikipedia. We had a few in the motor pool. I got well over 60 mpg on the highway - close to 70, and on a nearly pure stop n go trip to SF (clogged, on both freeway and city streets) got about 60. Had to retrain myself to shift when the light said to, which appeared to lug the engine a lot but gave the electric motor something to do (a pool car with a stick shift ... even though they only had a few, one was almost always available for checkout).

Edit: added wiki link

 

[Martin Penwald]

I

Check out the AeroVelo Eta, the speed bike that I worked on in university. It currently holds the human powered speed record - nearly 90 mph just with a buff guy pedaling.

We calculated our miles per gallon equivalent at 9544 MPGe. We never wind tunnel tested it, so not completely sure what the Cd ended up at, but it might be a little better than the TUDelft vehicle mentioned. Definitely better if you look at CdA, because we only have two wheels.

Awesome. I want one.
I see there isn't any window to watch outside, just a camera. I'ld like to ride it for fun, but it doesn't look very practical to go to work every day.