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How GM's grueling 24-hour test gets the kinks out of its performance cars

One of the biggest challenges automakers face when designing a high-performance car is making sure that it is both fast and reliable. For General Motors, any car that might be taken to the track by its owner - like the Corvette, Camaro Z/28 (shown above) and the Cadillac CTS-V, for example - undergoes a rigorous and strenuous 24-hour test by engineers at the Milford Proving Grounds, as pointed out by Car and Driver.
We've posted on this topic in the past - on a video showing the Camaro ZL1 being brutalized, for instance - but this article gives a more in-depth look at what actually happens behind the scenes... including what that poor ZL1 went through. Though the test isn't for 24 hours straight, the cars are pushed as hard as possible by some of GM's best drivers with only the brakes and tires replaced frequently.
We don't want to ruin the fun for you, but it is an interesting article that tells just some of what GM does to develop its sports cars. Check out the full article over at Car and Driver for the rest of the story.

Fullsize GM SUVs have a problem that's making owners sick

Some fullsize SUV owners are getting sick, thanks to a buffeting and vibration problem in 2015 model year examples of the Chevy Tahoe and Suburban, Cadillac Escalade, and GMC Yukon. According to owners' complaints to the National Highway Traffic Safety Administration, the issue can vary from an annoying vibration inside the cabin to an experience so severe that it leads to dizziness and headaches. General Motors is aware of the complaints, but the fix isn't so simple. According to spokesperson Tom Wilkinson to Autoblog, the company "has been tracking this issue for a while." The problem has a fairly low incidence rate, but when it does occur the issue can be "uncomfortable and annoying for owners." There's no precise cause for the issue, Wilkinson claims, and in some cases, simply balancing the tires or changing the door seals can make it go away. However, not all of the fixes are so simple. AutoGuide dug deep into the problem and discovered a GM preliminary information bulletin that advised dealers to remove the headliner and to check the roof's bonds to the bows that go across the vehicle. However, that document included a note that the solution might not entirely eliminate things. According to AutoGuide, adding Dynamat insulation to the roof sometimes helped the problem. A GM spokesperson also told AutoGuide the company fixed the problem at the end of the 2015 model year, and didn't go into any more detail. This roof issue seems linked to some of the worst droning in these SUVs. According to one complaint from a 2015 Suburban owner to NHTSA: "Roof will not remain attached to the roof bows. This causes the buffeting similar to a window being down when all are up. The results span from annoying to painful." A 2015 Yukon owner claims to have another alleged cause for the problem in a NHTSA complaint from February 2015. This person brought their SUV to the dealer seven times over the course of four weeks for vibrations. The dealer replaced the driveshaft, suspension components, and more, but nothing worked. According to an engineer to the service adviser: "In an effort to prevent roll overs, they designed the frame and body mounts too stiff. There are 40 engineers working on issues, they have no solutions that work across the board." Wilkinson told Autoblog that GM is working with customers on an individual basis to rectify things. Since these are newer vehicles, dealers should also fix the problem under warranty.

2015 Cadillac ATS Coupe First Drive

Save for a few years of its century-plus existence, Cadillac has offered its unique brand of American elegance in two-door, fixed-roof bodystyles. Most of these cars were big, floaty barges, of course, though its most recent offering was the wedge-shaped CTS Coupe. But whereas the CTS Coupe was a statement car – angular and severe, with somewhat limited appeal except to design snobs and provocateurs – the ATS Coupe represents a return to form for Cadillac, with a proper three-box (engine-cabin-trunk) body and a slightly lower price point that should broaden its appeal among a larger swath of the market. Generally speaking, the 2015 ATS Coupe is a two-door version of the sporty ATS Sedan, though, surprisingly, the only common exterior components are the hood, headlamps, and sundry trim pieces on the front fascia (which features a slightly larger grille, a wider lower air intake, and the redesigned, laurel-less Cadillac crest). Even the mirrors are different. The body stretches 0.8 inches in length and 1.4 inches in width, the roof is 1.1 inches lower and the rear windscreen slopes at a flatter, sleeker angle. Interestingly, the windowsills are actually quite a bit lower, further slimming the car. Thanks to its 0.8-inch wider front and rear wheel tracks as well as more tumblehome in the C-pillar area, the coupe sits lower and looks more planted than the ATS sedan, particularly from the rear three-quarter view. Filling the wheel wells is a family of slick 18x8-inch wheels, with 18x9-inchers coming on the rear axle of performance models. Even if all those changes haven't resulted in a wholly new look the way the CTS Coupe departs from its sedan progeny, the ATS two-door is a truly beautiful car that looks considerably better on the road than on a show stand. And for that, Cadillac deserves mighty praise. The ATS two-door is a truly beautiful car that looks considerably better on the road than on a show stand. It is a proper coupe, of course, and as such is saddled with the expected limitations that accompany modern two-door packaging, notably rear seat access and limited rear headroom. Since the floorpan is common to both bodystyles, rear legroom is the same as the sedan's, though headroom shrinks a considerable 1.8 inches, making it hard for even average-sized adults to sit back there without their heads touching the window glass.