The fastback having the highest lift reminds or brings back the Audi TT that had to get the spoiler lip because of how unstable it was

The Volkswagen Bug (or Beetle) was scary to drive at high speeds for various reasons, but one of them was how light the car became at those speeds; this demonstration explains the lift it’s body shape provided.

One winter night 15 years ago, when it was snowing and the conditions just right with the wind blowing steady along the travel direction of the parked cars in my street. There was one car, a hatchback (square back), which collected snow on the rear hatch in the wake zone, where the snow was capable of sticking. It formed a perfect boat tail: slightly curved sloping extension of the roofline, 10-15 degrees, as science tells us and the sides sloping similarly but at a somewhat steeper angle. What surprised me was that the edge between the sloping sides and roof line buildup, was a sharp perfect 90 degree edge. This must mean that the air from the sides and the roof stayed attached and didn't mix, i.e. no turbulence sideways across the snow cone! So it was a shame I didn't photograph it, but this is an example of real life simulation not based on moddeling. And thank you, your channel is brilliant. Nb.: the sloping sides of the snow cone met in the middle forming a sharp stump vertical edge there, so the buildup overall ressembled the stern of a round bottomed wooden boat.

And that is why lots of sleek FWD cars still have rear spoilers! Another great video, thanks!

Still fascinating, from a retired engineer, spending my life in a wind tunnel. It will be awesome if you can present a series of basic tutorials (again) for us car enthusiasts. My first car was a 1930 Chevrolet. This car had almost zero drag but then it also had very little speed. (Pun intended) My latest car is a Porsche. With speed, aerodynamics became really an important issue also as it directly affect fuel economy. So referring to basics explain again the basic shapes, ie a square compared to an aerofoil shape has almost 25 times higher drag for the same projected area. The exponential phenomenon of drag vs speed. Tyre width and tyre pressures. Open windows vs closed etc. Basic practical principles that already assist in saving money before vast monies are being spent on attachments. As it is still a specialized subject with lots of 'confidential' results, it will just be great if you provide basics for the next generation. Thanks for your dedication and passioin. Love from Africa.

Reminds me of when Volvo wanted to get into Touring Car Racing and before they built something slippery to get into the series quickly (you had to have a certain number of production cars before you could race that type) they went through their entire fleet to find the car with the best aerodynamics. Which is why, in all it's glory, the Volvo 850 Estate appeared on the starting grid in 1995 (with a production Cd of 0.32 I think). That has a lot to do with my Toyota Corolla Hybrid Estate outside!

I ride a motorcycle and am always amazed at how various vehicles create turbulence as I follow behind. It is not necessarily what one would expect. For example, smaller vehicles such as a Rav4 create quite a bit of turbulence as a result of the square back even though it is not large. A larger SUV with a rounded back is sometimes less turbulent. Many cars can't be felt at all.

Please do a video showcasing the various types of wings/spoilers affecting lift & drag. I want to fit a spoiler on my notchback vehicle for cosmetic purposes, but I'm interested in seeing the airflow effects. Thanks again!

How would this work on a large car like a 2008-2015 Nissan Armada. I have the running boards removed (the side steps) so the vehicle is very tall. I was wondering if covering the floor could help highway MPG, and I was also just wondering about the roof rack on it and if you had any opinions. The front hood does have one of those wings at the front tip. The car gets decent gas mileage going 70mph but once you hit 80+ it really takes a hit from wind efficiency. I was hoping I could get it to cruise at 80 with less force.

I have '15 Corolla sedan. The flow separation on back widow in the centerline is a thing. Very well seen during winter when it is the only place where snow wants to stay. However the airflow reattaches itself really fast from the sides. Only place where snow accumulates and stays is top center of the back window and bottom edge of rear hatch. I'd say it is really well designed.

This video is pure gold! Thanks a lot

Julian please help me... I got a Suzuki Ignis 2004 MH a quite blocke body shame of car... If I abb the factory rear spoiler will it help with the fuel efficiency any? I know it will give an extra downforce on the rear wheels but will it also help by redirecting the air with the fuel efficiency or will it a drag? thanks a lot

Really interesting video - thank you!

Can you please make a video about the airflow around the tires? I see different ways in which manufacturers try to deflect the air before the tire

Great knowledge! It would be awesome to know your thoughts/experience regarding momentum injection into the wake. Something I often ponder :)

Makes sense why Germans love their fast station wagons :) I see that bubble on my notchback every winter. Snow just sits in the bubble and doesn't get cleared away.

Very interesting. Thank you for this very informative video!

Fantastic! Wonderful find - thank you for sharing! Nice to finally see someone has confirmed with research what I’ve understood from driving my squareback: when I’m driving and have a significant enough wind to fill the wake from behind, in the same direction I’m travelling (a tailwind or rear quartering crosswind), my fuel economy improves (not insignificantly). So now, it seems I have to get the air from over the roof and underneath the car into the wake sooner to reduce it, and hopefully drag along with it. I’m going to make an educated (from this channel’s videos) guess that it will take an undertray with a rather serious rear diffuser bringing the air from underneath upwards, as well as a roof extension lip curved downwards towards the road to fill in the wake area.

I am very lucky to own a 1997 Tommy kaira M20b wagon, with a custom made TK roof spoiler, which was experimentally set for minimum drag in the wind tunnel. The custom TK parts all have little metal plates with the TK signature on them. Tommy Kaira were engineers before all else, and they recognised the frailty of the Subaru 5-speed box in the JDM WRX the car is based on, and so they created two massive braces which go straight through the 'box hold it together, preventing it performing a RUD (Rapid Unscheduled Disassembly) at high boost and high RPMs. :)

Awesome, thank you for your enthusiasm, too makes it more interesting. I’m wondering if a spoiler like a ducktail or those small wing tails actually make a difference too.

Very interesting my hatchback "square back" has less lift. It never feels like it is light or floating at high speeds, that is suspension also.

It would be interesting to see this study for semi-trucks, pickups & the Aptera !

Hi there,quick question I have a 1997 blazer drag/street project and was wondering if adding a rear spoiler would increase her aerodynamics overall?

I found my book suggestion for this christmas :)

It looks better. It makes the car worse. - I can see the designers and engineers having this argument all over the world. As the manufacturing engineers and workers say "I can't build either one." and the mechanics: "That oil filter is where!!!"

Hi Julian: If you could break this down into a tiny nutshell, which shape would yield the highest MPG at 100 km/h? I always assumed the fastback/kamback shape was lowest drag overall. Your channel is much appreciated.

Just what I was looking for

If the front of the car is the same what makes the Clf so different between configurations? Is it because of the lift occurring behind the rear wheels and leveraging the front up (or down)?

I have an A6 Avant (so a Sqaureback) It's stability at high speed (tops out at 250 kph) is amazing. Just planted. I've had other wagons and always suspected this. Conversely an RX2 I had in my youth was like piloting a skimming stone

This reminds me of a photo I saw of a Datsun 240Z at speed, lifted right up on its suspension; no wonder mine felt much better once I added the rear bobtail and front airdam! It actually increased its top speed by about 15km/h too, so the drag must have dropped.

Question: around 7:48’ish, you mention the drag / wake shape is 3D not 2D. Should not the diffuser then be designed / shaped to take this into account and thereby maximise the impact of the diffuser? Or am I just totally ignorant with the relationship between the wake pressures in vehicles with diffusers vs no diffusers…

Would love to see visual representation of how adding some vortex generators across the roof affect the lift and the blue bubbles behind the body shapes.

Great video. I have a flat bottom drag car that travels over 300km/h. Would ducting from front floor to the tail lights reduce pressure under the car and reduce drag at the rear? Thanks for the great vid

hi, im just a normal human from the street so i don't really understand the theoretical stuff. could you please tell me in few words if it's recommended to install the Backspoiler (hard-plastic fixed with screws) on my Palio 1.8r or no? :( the original Fiat Palio 1.8r 2008 has the spoiler yes but i would like to know if its recommended to have this spoiler or no

Wish I could see a presentation from above the 3 vehicles, that would prove interesting

apart from being a brickwall; have you seen anything on the the 4x4 model, like the landrover, g-wagon, etc?

The Julian Edgar, 21 century performance was a stellar book mate

This is really interesting, although these figures can only be generic because of the significant detail differences between different vehicles. It would have been interesting to see figs for a true Kamm tail as well. And what I would _really_ like to see would be CD figures for the sleek E-type jag and the extremely boxy Austin A40 Farina. Rumour has it that the A40 is actually slipperier.

I would like to have seen the Kram theory rear used also. The hollowed out rear seems to have the reported push in real life. A good example of this is the Chrysler Australia Charger, it was a fast back with a Kram theory shape below the boot lit. When these cars were used in outback Australia they got lots of dust embedded in the hollow of the rear end in the dry and a mud coating when it was wet.

The SAAB NG900 had to get the small spoiler added because of stability issues at speeds above 170kph.

brother, are you _certain_ you got your colors right, warm/cold _ red/blue?

How would you inprove the tail l on this car ukposts.info/have/v-deo/hXiIiGZnnYyqrX0.html&ab_channel=BoostedBoiz

The notchback is the winner overall. The higher front lift counterbalance the rear lift and makes it stable at high speed

Sounds like you might as well use at least a fastback shape, and a squareback really only adds a tiny bit of drag, but both of those have much more payload volume in back. Notchback looks aero but isn't any better than fastback.

Hi Julian,great video!how about the aerodynamic at bed on the pick up trucks with or without roll top cover on it?ive not find any video about it,also the sunroof,widly open or shark open?thanks for this awesome knowledge!

Hi Julian, Is there a "spoiler" to reduce the centerline low pressure effect? Also good to see this from your Zoom days

Hi Julian would you be able to do a video on the aerodynamics of utes? I have a VE commodore that I am wanting to improve the aerodynamics of and would like to see someone else’s opinion on how to reduce airflow separation between the roof and hard lid cover of my tray while retaining a mostly OEM look. Hope you have a nice day mate

what I learned - wagons (hatchback) rule; other cars can drool (oh snap, Prius be damned) And it looks like my '19 WRX is hamstrung from the get go, not only being a Subaru, but also being a notchback (w/a trunk or boot). Might need to add one of those gurney flaps to the low profile trunk lip spoiler to push that air higher off the back of the trunk (as I do not have the big STI wing). Wonder if those vortex generators will reduce that high pressure on the rear glass area?

Very nice video... I have watched many of them... Ok with the hatchbacks... What about the coupés and the Roadsters?? I have a BMW Z3 Roadster Cd:0.42... Roof down 0.55... What could i do to improve these numbers?? Should i use a flat bottom??

Stumbling on this video years after it came out, but it's nice to see data that matches what I see in real life. Having an extreme squareback (minivan) it just confirms my suspicions as to what I've seen when driving: I've seen leaves picked up from the road just move around horizontally in the rear glass and just stay there floating, and living in the dusty desert, the rear hatch of the car is always covered in dust/sand, no matter how often I wash or what wax products I use, I can mitigate it but I've resigned myself to always have some dust collecting there. My other car (a wagon, Subaru Outback specifically) also see this but to a different degree: Years of being exposed to this same dusty environment and about an inch long lip on the rear hatch near where the rear wiper is now at this point sans clear coat, no matter my efforts at trying different coatings.

Am I correct to think that there are no separation edges on particularly the squareback model? If there were, the offset airflow diagram might suggest they aren't that effective, 19cm is not far offset from the centre line. Interesting that the slow moving air seems to extend further out to the sides and low down on the notch and fast backs compared to the squareback.

Does that mean that the squareback is the safest as in most contact with the road?

Beautifully consistent with theory. One thing: these two, I'll call them measurement planes, are only 20cm apart right?

Looks like both the fast and notch backs would benefit significantly from a modest bob tail spoiler. Likely to bring them up to square back figures I wonder.

Being the front part of the model the same, why is the Squareback Clf so different to the other two? I don't understand it?

super interesting video, i was secretly hoping to see the legendary Lexus LS400 in this video though. the most aerodynamic land yacht in history.

Cool to see that hot hatch is actually the best body type aero-wise, it generates a bit of downforce without any additional aero.

If there was a book like this for motorcycle windscreens it’d probably sell like mini donuts during crazy day at the shopping center.

On a 2017 Civic what would overall effect on Cd be with using panels to create a flatter floor in rear 1/3? The factory mufflers were removed and now I fear that the rear bumper acts as a parachute. The front 2/3 of car already has flat floor coverings.

Have any information on pickup truck aero? Interested in the effectiveness of cab spoilers and tail gate spoilers.

Makes me wonder how my old Brick of a car a volvo 945 station wagon would do in a modern wind tunnel.

nice video!!

I was read this essay thank you

I appreciate your attention to flow and drag. An area that *should have been central to automotive design at least 3 decades earlier. Question though, wouldn't these comparisons be more useful with an attached flow fastback? I thought attached flow was the whole point of the fastback

Hello i have just purchased your latest book from amazon so on my way next with tuft testing Where would my car fit into this test as its non of the above shapes 1961 ford anglia 105e

My Jaguar XF has a little aerodynamic ‘lip’ just above the rear window. I don’t think it’s there to provide attached airflow, I think it acts as a high speed stabiliser

After watching some more of your videos regarding vehicle aero you talked about your Honda Insight (I think was the model). That you did some aero modifications to had a spoiler or whatever you called it. How would someone know how to add or modify a spoiler (size, angle, location, etc.to actually be beneficial and not just add drag and hurt performance? Thanks

great!

underrated vid.

@Julian Edgar - I'm a fan of your video series! @3:24, on the comparison table, it seems that bluff / squareback shapes are slightly higher in drag, but have massively lower lift in both the front and rear. Given that Cd mostly impacts top speed (bragging rights but limited relevance in the real world) and fuel economy (lower priority for buyers of expensive performance cars), why aren't Ferraris, Lamborghinis, Porsche, 'Vettes, etc, shaped more like estate / wagons? It seems to me that low Cl is a higher priority than Cd in this niche market. Thoughts?

Very interesting, I wonder what effect 2 ducts from the rear wheel arches (or some area with known high pressure) to the back of the car would have, would they help equalize the pressure in the back and lower cod? Similar to a very aggressive rear diffuser but trying to keep the shape of the car, to preserve the practicality

I drive a van with basically a 90 degree tail. Any amount of moisture or dust, and the back is covered in crud due to aerodynamics.

Thanks for your explanations. Drag and lift is a very very interesting topic. I have seen a lot of conclusions in the comments in regarding to stability. But I would say, the stability difference between the body shapes are very low in modern cars. More important for non track used cars are the speed of air flow, because of effiency. Thats why sportback shapes are faster in accelaration, espacially at higher speed, producing higher top speed and less fuel consumption. You can really good obeserve that at the German Autobahn. Anyway, I would love to see the effects of rear and front spoilers in regarding of different body shapes. Thank you in advanced!

From 8:22 … would love to see this pressure map from above …. Looking down on the airflow. Excellent Stuff !

wish you would make some more videos

It should be possible to transform turbulent flow into laminar flow by changing the shape of the hood and roof, making it go through a tight space for compression and separation and then gradual and linear compression. What is presented here is just a result of the front side of the car going through the air. It's also interesting to take a look at a side profile to create gaps that would smoothen the airflow or the car's wheels as well as making it more droplet like shape overall. Its well known to design the bottom of the car with aerodynamic splitters that both create directed airflow providing cooling and creating less lift, so there less downforce needed to be compensated.

Just had this video appear in my recommendations, very interesting it is too. One thing, at 6:30 you mention the front stagnation region, in the real world this would be different with airflow through the grill.

I have a question and would really appreciate if anyone knows the answer. Whats the best car body shape to carry pushbikes mounted on towbar(behind the car) most efficiently? Any help much obliged!

@Julian Edgar Hi, i am discussing air drag with a friend. He drives a Lorry in the NEtherlands. A 2014 Truck. He pulls a tanker behind him, basically a "pipe" on wheels. but on the top ie left and right next to the pipe a grid, where workers can walk on. this grid has holes so it is lighter and the grid "fins" are vertical, have different height and a slightly inclined shape to give more hold. i wounder how high the air drag is and if we could solve it by putting a "plank" on the grid. If you know who i could ask to solve this, or if you have read it but cant find a quick answer, i would love a feedback if you have read this. Thanks in Advance

R H BArnard was my teacher at Uni :)

Super.

As noted the aerodynamics considered is partial, so the actual lift and downforce values may be a bit different. What did seem to be left out is the airflow below the vehicle and for anyone familiar with Formula 1 these days the floor plays a vital role for the car. Just slight changes in the suspension geometry could give different result on downforce due to the changes in airflow under the car.

I camt decide whats best for my 65 mustang coupe,thinking of a drag style tail with a slight increasing angle,or just a small duck tail,anyone got suggestions?

Looks like the combi (squerback) is best for normal driving.

We have 2 different car roughly similar size is it possible that car 0,3 drag coefficient and car 0,23 that car with higher drag coefficient number have still better efficiency if body type in those are different. Or is it always lowest number win?

thats why on some cars you have sand papered licence plates in the back

This is what YT was meant for

The Civic looks LAUGHABLE

So if you got a notch back get vortex generators & a spoiler. Fast back just get vortex generators because most already have spoilers

I guess this explains why so many cars look the same these days. Their body shapes are optimized for aerodynamic properties, and since there is only one optimal shape for each basic configuration, they all look the same.

Fascinating topic. Well put mate. Sadly no data for hatchbacks

would this be the reason why volvo raced the 850R wagon in the British Touring Car championship??

theres a reason why Richard Feynman once called turbulence “the most important unsolved problem of classical physics.” whether its the founders of quantum mechanics, or the OG classical physicists, it seems like every smart person ive learned about has spent some time pondering aerodynamics. from einsteins contributions to brownian motion, to leonardo da vinci's drawings of mechanical inventions, it seems like aero has fascinated and surprised everyone. not to sound like a sociopath, but sometimes I put wedge my cig buts on the back of my car and am suprized at how they may or may not still be there after driving on the highway depending on the car shape and location lol.

what's the solution to overcome drag on the rear for notchback?

Interesting video YT threw at me. I ride a motorbike and when on the motorway, some cars create the most awful turbulance i just can't figure how modern cars would be so bad. So I was curious to see what this video revealed. To be fair, the distance I travel behind other vehicles means this video doesn't quite cover my query, but it remains interesting. What i have leant in general is that on the motorway, estate cars seem better, with a cleaner, less turbulant wake. But it's not obvious, as some slippery looking cars generate awful wakes. This wake turbulance is effective at 150-250m behind the vehicles. I tend to overtake these and get ahead, but sometimes people cut in front of you at much shorter distances and the wake can be a real pita!

I would like to see a 3d visualization of this.

9:18 could you explain why there is a higher speed flow near the edges of the car compared to the centreline?

What's the best?

I would like to see this same test done with roof rails installed to see what the disturbance and impact is.

How is the airflow under the body modelled here, to meet and integrate with the top flow as they would affect each other?