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Old 02-28-2013, 07:12 PM   #1

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Vette Engineering Manager Explains C7 Chassis

Sorry if this is a repost, but I found it quite interesting.
Detroit Ė Chevroletís glitzy Detroit show premiere of the C7 Corvette Stingray stands as the car debut of this very young year. Exterior and interior design reviews are overwhelmingly positive, and the enthusiast media are anxious to test the 450-plus-horsepower small-block that gets more than 26 mpg on the highway. The Corvetteís ride and handling have come a long way over generations C5 and C6, and General Motors believes it has a world-class sports car with the C7. Josh Holder, program engineering manager, is in charge of assuring that the new Stingray is Chevroletís most refined, world-class sports car ever. This is Holderís third Corvette. He also has worked on the Cadillac XLR, the GMT800 full-size pickups, the Pontiac Solstice/Saturn Sky Kappa twins, and the Chevy Camaro. He also owns five Corvettes. Holder gave Automobile Magazine contributor Marc Noordeloos a few hints about what to expect when we get behind the wheel of the 2014 Corvette Stingray this summer. Hereís what he said:
MN: What ride and handling traits of the C6 did you want to fix for the C7?
JH: We wanted to expand on a great car. With the new Michelin tires, the base C7 will be capable of over 1.0 g lateral grip. The suspension layout is basically the same, but the track is wider and we moved the center of gravity toward the rear. We think weíll have a 51-percent rear bias. Some of that was achieved by extending the front tires forward one inch to package the new engine and its hardware for fuel management, but it also improved weight distribution.
MN: Did you consider replacing the transverse leaf springs?
JH: We prefer to call it a transverse composite spring! Its manufacturing technology enables a low mass, a low center of gravity spring versus a conventional coil-over. It packages very well. The supplier has many patents, some they donít even tell us about. It reduces roll without giant anti-sway bars. The biggest evolution is the third-generation MR (magneto-rheological) dampers. They use a dual-coil setup that cuts the interference of one magnetic field from another and speeds response time by up to 40 percent.
MN: What are the core differences between the standard car and the Z51?
JH: The biggest difference is roll stiffness. The base car has no rear anti-roll bar and a smaller front bar for a better ride. The base car also comes with a taller [aspect ratio] tire. Overall diameter is the same. The base car has an 18-inch front/19-inch rear setup. The Z51 has 19-inch front/20-inch rear. The Z51 has more on-center feel and more response, but itís more sensitive to road disturbances. The standard passive dampers are tuned largely for the track. The Z51ís optional MR dampers, in their extreme setting, are just a touch stiffer than the passive damper, while the softest setting is much, much softer. We look at the active-damper-equipped Z51 as the no-compromises car. You get the ultimate in track performance and handling without a harsh ride.
MN: How do you tune the Corvetteís first electric power steering?
JH: The industry is going to electric power steering, so the supply base and technology have expanded much from five years ago. EPS offers fuel economy and horsepower benefits. Our biggest concern is compromised road sensitivity or feel. Our experience in integrating it into the car has shown no such compromises. We also stiffened the linkage and other steering components [to] six times the C6ís stiffness. Our mode-selector shift lets the driver set sensitivity and steering effort. For the track, you can increase the effort and sensitivity.
MN: What do aerodynamic and downforce development do for dynamics and performance?
JH: We have a rolling-road aero of 0.28 with reduced coefficient of front and rear lift. That helps lateral tractive effort for reduced understeer and more traction on corner exit. We are exiting roughly one-third of the radiator airflow through the top of the hood. Whatís normally a big, high-pressure area on a front-breathing car now has a pressure release on the top of the hood. The NACA ducts in the fender also relieve some of that. Z51 has a standard rear spoiler and rear diffuser to keep air attached to the bottom of the car, generate low pressure, and keep the rear downforce in check. We spend many hours on aero in the drive for fuel economy. The balance between drag and lift is unprecedented. Itís safe to say every exterior surface is more than beauty. Surface designs either reduce drag, reduce lift, improve cooling, or do all three.
MN: Will you tune differently for Europe? How about right-hand-drive?
JH: There are no plans for right-hand drive. Itís a much bigger deal then just moving the steering wheel. Weíve retuned the European chassis. The MR suspension calibrations are different. We will make spring rate changes if needed, but we are not planning to do that. Every car that goes to Europe and the Middle East has Z51 cooling as standard equipment. Much of the European-specific tuning work is done and validated on real roads, like the autobahn and the NŁrburgring.
MN: What key competitors did you benchmark?
JH: We spent time in cars like the Porsche 911and the Ferrari 458. Itís hard to say that we benchmarked those cars. We evaluate competitive cars, as everyone does. Any time we do a new Corvette, we are only somewhat influenced by competitors. We are largely influenced by what we think the car should be.
MN: The new Corvetteís electronic limited-slip differential is quite complicated.
JH: The e-LSD can go from nearly open to fully locked. This allows tailoring in corners and improved handling dynamics. When youíre in a yaw rate change, it can lock and unlock accordingly to maintain control. In a conventional differential, you get some body roll upon transitionsówhat we call head toss. With the e-LSD, the car feels planted in those conditions. With the traction control features active, you can matt the throttle with the wheel at full lock and power out of a corner. Itís a pretty amazing setup. The Performance Traction Management option offers five levels of active handling on the Z51.
MN: What do the new Michelin Super Sport tires do for the carís performance? Did you consider moving away from run-flats?
JH: We donít just develop requirements and then pick a supplier. We have a bona fide competition between tire manufacturers. We give them a rough set of requirements, one of which is run-flat technology [zero-pressure, at-speed, to a certain distance]. The structure of the sidewall for run-flat technology has evolved so you can now get a quiet, compliant tire. The tires are [Michelin] Super Sport ZPs, which have tremendous grip. They telegraph very well at the limit, with excellent feedback, and good wear resistance for performance tires. We canít just throw in a can of fix-a-flat. We have systems, and we have to validate everything.
MN: How much do older, core Corvette buyers influence the new car? Does it always have to be front-engined?
JH: They certainly have influence. But we always look to the future. A lot of people have asked Ö why we didnít do a split-window or other details like that. The car needs to continue to look toward the future. We evaluate engine placement, as not all Corvettes necessarily need to be front-engine cars. Front engine still remains the best balance, best optimization of what we feel the car needs to be. This [the C7] is a clean-slate car. Two carry-over parts [cabin filter and roof latch], thatís it.
MN: Was the Stingray name a way to push the car forward while retaining traditional buyers.
JH: We see the original 1963 Stingray as the best, a groundbreaking car in terms of technology, design, and performance. After the C7ís design was frozen, we decided to call it Stingray. The decision wasnít taken lightly. It does indeed ring with our loyal buyers.
MN: Iíve always respected the Corvette, but Iím not a target customer. How would you get me to consider one over a Porsche 911 or Cayman, or a BMW M3?
JH: The Corvette is a great value. We think the new car delivers on that aspirational goal. When you get a chance to drive the car, you are really going to be blown away. The new car delivers with the new interior and comfortable new seats that make the car feel like itís wrapped around you, like itís an extension of yourself. Visually, we think we have what it takes to get those buyers interested. A guy like you falls into our target market.
MN: What about a ďminimalistĒ version?
JH: I own a C6 Z06 that has zero options, a very rare car. You can option a Z51 that way now. Some purists, like me, think it would be cool to have a car with no radio and no A/C. Itís fun to think about, but when you look at real sales, itís not as tangible as we all would like. Still, you can get a bare-bones Z51 for the purist.
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Old 02-28-2013, 07:40 PM   #2
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Originally Posted by mikeyg36 View Post
Sorry if this is a repost, but I found it quite interesting.
Great read
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Old 02-28-2013, 08:17 PM   #3
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Great article and packed with information. The car sounds better and better.
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