The Truth About Cars » aero The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Wed, 23 Jul 2014 18:25:17 +0000 en-US hourly 1 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » aero A Visit To Ford’s Wind Tunnel To Look At The New Mustang’s Slick Aero Tricks Sat, 01 Mar 2014 18:00:55 +0000

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The second best part about the job of writing about cars is not getting to drive expensive cars for free or being flown to resorts with Jacuzzi tubs. No, the second best part about the gig is that I get to see and do some very cool car guy things. How many of you have watched film or video of a car being tested in a wind tunnel and thought to yourself, “that’s neat!”? Well, this week I got to observe the new 2015 Ford Mustang’s aerodynamic features demonstrated in one of those neat wind tunnels.

As part of the publicity campaign leading up to the April introduction of the all-new 2015 Ford Mustang, Ford is going to have a series of presentations to Detroit area automotive media types and they kicked it off with a visit to FoMoCo’s Driveability Testing  Facility in Allen Park. The DTF contains a number of test cells that allow Ford engineers to duplicate just about any temperature, altitude or meteorological condition (including snow and hail) a driver might experience. Three of the test cells are wind tunnels large enough to test full size cars and Ford’s marketing and engineering folks had a preproduction black 2015 Mustang GT coupe sitting in one of them.

After Kemal Curić, who was in charge of exterior design on the new Mustang, did a walkaround, pointing out the various aerodynamic features of the car, they fired up the fans to 30 mph and a technician used a smoke wand so we could actually see just how effective those features are.

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When the 2015 Mustang finally hits the showrooms later this year, you may not notice the differences, but each of the models has been fine tuned for aerodynamic balance. Ford says that they spent twice as much time on the new Mustang’s aerodynamic performance as on the outgoing model. Much of that work was done in the digital domain, which can work at a very fine granular resolution that can’t be replicated with real-world pressure sensors or physical tufts, but still everything is subjected to real-world testing with real airflow in a wind tunnel.


Some of the changes are almost imperceptible, for example, raising or shaving the surface of the rear deck lid by as little as 1 millimeter will have an observable and significant effect. Each model, Ecoboost 4, V6 or GT, has slightly different aero features and if you order the performance package on the GT, that gets its own special wind-cheating tricks. For example, EcoBoost powered Mustangs will feature active grille shutters that close to reduce drag at higher speeds. Different front splitters and functional rear underbody air extractors were developed for each model. The front fascia on all models incorporates ducts that create aero wheel curtains that isolate the spinning wheels and tires from turbulence, a first for Ford.

Wheel aero curtains on the 2015 Mustang

Wheel aero curtains on the 2015 Mustang

Most of the work is aimed at reducing turbulence and hence drag by keeping the airflow closely attached to the car body’s surface as it passes the car. With the smoke wand set right at the leading edge of the hood, the trail smoothly runs from the nose of the car up over the roof and then down the fastback roofline and over the integrated spoiler on the deck lid. It’s only when the smoke is finally trailing the car that you see any turbulence, though as it transitions past the functional cold air intake for the engine at the base of the windshield you can see the eddies curling air down into the induction system.


Another of the aero features of the front end are functional air extractors in the hood. Not only do they prevent air pressure from building up under the hood, Curić said that they actually create downforce. Moving back along the car, the side mirrors have been moved from the window frame down to a stalk on the door. That aerodynamically isolates the mirror from the body, allowing laminar flow along the window. The mirror itself has been shaped so that air flows smoothly around and past it. A side skirt below the rocker panel works with the front splitter to keep underbody airflow separate from the upper air. One aero device you might not notice is a small flap spoiler mounted under the car just in front of each rear wheel, intended to smooth the flow of air around the rear tires.


The rear decklid of the new Mustang GT is the collaborative product of the designers, aerodynamicists and the manufacturing engineers. You may not realize this when you see the complex shapes on modern cars, but there’s a constant struggle between the designers and the body engineers over what is possible, or more importantly, what is possible at a price point. The decklid on the 2015 Mustang is a relatively complicated shape, particularly because they decided on an integrated spoiler, not a bolt on part. It’s one thing to get a clay model to perform well in the wind tunnel, it’s another thing to be able to reproduce that shape in metal or plastic production parts.


One reason why they don’t just rely on testing aero with fluid dynamics in the digital domain is that the wind tunnel isn’t just used for aerodynamics. Microphone arrays mounted above and to the side of the car are used to measure noise and are part of the process of reducing NVH. Interior sound measurements are taken with the audio equivalent of crash test dummies, but I was told that exterior measurements correlate well with how much noise there is inside the car, which makes sense.

IMG_0027At the event I learned a little bit about how they do wind tunnel testing at Ford and how that affects the way the new Mustang looks and drives. I also learned a bit about just how serious the Ford engineers and designers are about wringing out a small percentage improvement here and another one there. When it comes to aero, all those little things add up. Though they wouldn’t cite a specific drag coefficient, we were told that the new Mustang is 3% better in terms of aerodynamics than the 2014 model, yielding a 1% improvement in highway fuel economy. As you can see from the acoustic testing, though, it’s not only about miles per gallon.

Almost one in five Mustangs that are sold currently are convertibles. Before the wind tunnel presentation we heard about the Webasto supplied folding roof on the new Mustang convertible and how it’s quieter, goes up and down faster (an electromechanical drive replaces hydraulics), folds flatter, looks better both up and down, and, yes, has better aerodynamics than the ragtop on the outgoing model. The old roof had three supporting bows, a vinyl outer skin and an inexpensive inner skin. The new roof has an additional bow to give the roof better shape, the outside is fabric, the inside is real headlining material and between them, for the first time on a Mustang, is a layer of sound and heat insulating foam. One of the reporters asked them if the improvements were made in response to consumer feedback. The Ford engineer replied that yes, they had gotten feedback indicating that Mustang owners wanted a quieter car, and then, almost as an aside, he said, they wanted to give the new Mustang a better roof in general.

It’s quite difficult to convey to people just how massive an undertaking it is to develop a new car. I’m sure that what I saw at Ford is duplicated at every major car company. Because of this job I get a peak behind the curtain now and then and I get to pay attention to the men and women working behind that curtain. However, instead of charlatans pulling levers projecting the image of greatness, there are lots of very hardworking people making great efforts at incremental improvements that, taken cumulatively, positively impact our experiences as drivers and car owners.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can get a parallax view at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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Review: 2010 Saab 9-5 Aero Fri, 08 Oct 2010 18:05:46 +0000

Back in 1983, my father, entranced by its idiosyncracy, nearly bought a Saab 900 Turbo. He even would have bought one, but with Detroit showing new signs of life I was on a “buy American” kick (the decade ultimately cured me). So he ended up buying the second-place finisher in Car & Driver’s infamous Baja comparison test instead. Down the road very different qualities drew him to Lexus. Apparently, Saab wants him back. How else to explain the new 9-5?

The new 9-5 looks about as much like a Saab as a car based on GM’s second-gen Epsilon platform possibly could. The rounded nose, curved windshield, and sweeping C-pillar provide clear visual links to that 1983 900 Turbo. No one will mistake it for the related Buick LaCrosse. And yet, not so Saabish: a high beltline, and the evident size of the car. Compared to the antiquated sedan it replaced, the new 9-5 is over half a foot longer (197.2”) and three inches wider (73.5”). It’s a big car, and appears even larger and more massive than it is. Handsome, perhaps, but neither striking enough nor distinctive enough to draw in new buyers the way the 900 did back in the mid-80s.

To Saab’s credit, they’ve clearly worked hard to retain the marque’s defining characteristics within the new 9-5’s interior. Sweeping fighter jet-inspired IP, egg crate air vents, start button between the seats (now keyless)—all present and accounted for. Aside from the aforementioned high belt, brand loyalists should feel at home. But how many are seeking a car this large, and are willing to spend so much for it? How many Saabistas are there at this point, period? Nearly everyone else shopping for a $50,000+ sedan is likely to be turned off by the predominance of black plastic. The leather seats look the part, and the design of the door-mounted upholstered armrests is interesting, but these cannot compensate for the stark ambiance and an IP that would look cheap in a car half the 9-5’s price.

Saabs have been blessed with excellent seats since at least 1983, and the new car’s are no exception. The front buckets are firm, yet comfortable, and provide much better lateral support than the typical GM parts. The back seat is nearly as comfortable and very roomy—as it should be given the car’s exterior dimensions. This is the size the S80, with nearly four fewer inches of rear legroom, should have been. But should the new 9-5 have been the size of the S80?

At launch, the 9-5’s only available powertrain is a 300-horspower turbocharged 2.8-liter V6 driving all four wheels through a six-speed automatic. Even burdened by 4,400 pounds (plus passengers), this engine accelerates the car with no apparent strain. In fact, no apparent anything. Even at the 5,500 rpm power peak the boosted six remains nearly silent. After the drive I popped the hood, expecting to find the engine fully encapsulated. Nothing looked out of the ordinary, but something most certainly is. Partly because of the engine’s almost eerie silence, the car never feels quick.

Given the new 9-5’s size, mass, and genetics, agile handling is out of the question. The active rear differential is no more evident than in other GM applications. On the pavement throttle-induced oversteer will be sought in vain. But understeer is almost equally elusive. For a nose-heavy car, the 9-5 possesses commendable balance and poise, with a tautness you won’t find even in the latest, German-engineered Buicks. The well-weighted steering is firm, especially in “sport mode,” which for once makes an obvious difference. The 9-5 can be hustled along a curvy road, if need be, and will feel better than the current Mercedes E-Class in the process. For better or worse, it just won’t feel like it’s hustling.

As with the engine, the wind and the road have been nearly silenced. Even the clomping of the tires over road imperfections seems faint and distant. The ride is smooth regardless of which mode is selected—if “sport” had an effect on the auto-adjusting shocks, I didn’t notice it.

I still can’t get my head around a Saab that’s so smooth, so quiet, and so large. There were clearly top priorities. But should they have been? Saab’s Swedish cost structure forces it to charge luxury car prices, so it must provide suitable levels of luxury and refinement. It’s also usually easier to get a higher price for a larger car. But unless a Saab retains the idiosyncracies for which the marque is known, why would anyone buy it? With the styling, and especially the interior styling, they opted to make the new 9-5 distinctively a Saab. But, drive the car, and this styling seems a veneer over what’s essentially a very well behaved Swedish Lexus. Though not soft like a Lexus, the new 9-5 manages to be surprisingly silent and smooth, and so insufficiently engaging. The evident charisma of that 1983 900 Turbo has been sacrificed. It’s not just Saab, of course. A Mercedes E-Class is completely soulless, and even BMW has been heading in this direction.

But was this “Swedish Lexus” a viable solution for Saab? Perhaps now would have been the right time to once again buck industry trends and truly do their own thing? We’ll probably never know. With the company striking out on its own and hanging by a thread, even most people who might have bought a new 9-5 now won’t.

Michael Karesh owns and operates TrueDelta, an online source of automotive reliability and pricing data

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NASCAR Tech: It’s A Lot More Than You Think Thu, 05 Aug 2010 15:43:11 +0000

I’ve heard a lot of derisive comments about NASCAR lately on this site, many of them from people — my fellow racers and fast-road drivers — who should know better. While it’s true that the common template is a disgrace, the idea that NASCAR is a low-tech ghetto compared to the oh-so-modern sports-car series like the ALMS is, to put it mildly, false. There’s a reason that the abortive USF1 team wanted to locate near the NASCAR guys. It’s where the tech is. Click the jump to find out why racing NASCAR takes more brainpower than any Touring Car or prototype series out there…

Let’s start with engines. NASCAR just runs old small-block Chevys with carbs, right? Not so simple. Let’s compare F1 engines to NASCAR engines using Brake Mean Effective Pressure (BMEP) and Mean Piston Speed (MPS). These are measurements of how hard and fast an engine runs. Surely the F1 engine runs at pressures and piston speeds that are FAR beyond those of NASCAR, right?

According to Race Engine Technology, The BMEP of the Formula One engine at peak torque (table line 13) is 15.17 bar while the Cup engine produces a peak torque BMEP of 15.12 bar (0.3 % less). At peak power, the Formula One BMEP value (table line 22) is 14.6 bar while the Cup figure is 14.0 bar (4.1% less). As far as piston speed,

Even more revealing, at peak power RPM (table line 19) the Formula One engine MPS is 25.5 m/s (5025 ft/min), while that of the Cup engine is less than 3% lower at 24.8 m/s (4875 ft/min). At redline, the Formula One MPS is 26.5 m/sec, while the Cup MPS is a stunning 27.5 m/sec. To put those numbers in perspective, Professor Gordon Blair wrote (Race Engine Technology, issue 27) that 26.5 m/sec was the highest he had seen.

How’d those stupid hicks get their pistons to move faster than the mighty engine builders of Formula One? Note that some street cars reach into the same piston-speed zone, but they are incapable of operating under those BMEPs for very long. F1 engines run with much greater friction to create those piston speeds because their crankshafts run faster… but NASCAR engines have a much longer stroke, thus imposing a much greater acceleration load on the parts.

Now let’s talk aero. With millions of dollars at stake, aerodynamic improvements are critical. ALMS designers can draw almost anything they want, because the rules are loose. F1 presents a much stronger challenge, which is why Nick Wirth’s CFD approach was so dominating with the LC75-based Acura ARX but has struggled to keep Virgin Racing from the bottom of the field. The limits to what you can “draw” in F1 are considerable, and any bright ideas don’t last too long, as was shown with the F-duct and flexible front wing that arrived this year and were promptly written out of next year’s rulebook.

NASCAR teams have an even tougher job. They are limited to a common template, so they can’t change the aero at all. Right? If that’s the case, then why is the Holy Grail of aerodynamic testing — the “coastdown tunnel” — rumored to exist right now, in the hands of Chip Ganassi? The answer is that NASCAR teams work at a level of aerodynamics unknown outside the world of military aviation: surface composition aero. A NASCAR Car of Tomorrow is a matrix of multiple surfaces, some smooth, some rough, all designed to manage the airflow at the near-molecular level. Jimmie Johnson’s remarkable pace last year? All the product of rough-surface aero development.

We could go on and talk about the massive effort put into the “little things” of racing — from the kind of brake compounds required to slow a NASCAR-sized sedan from 195+mph to the astoundingly complex calculations of shock absorber valving required to keep a car that big from becoming murderously loose on a bumpy superspeedway — but I hope I’ve encouraged at least some of you to go take a look at what actually happens in NASCAR. It may not be Formula One, but it’s not ALMS P2 either.

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