Project C7 Corvette Stingray: Introduction Part 1

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The C7's aluminum chassis is a work of engineering art.  It is one of the most sophisticated chassis found on a production car of any price point. 

The C7 chassis is a complicated aluminum structure consisting of 10 investment cast nodes (stiff structures where major components like suspension and powertrain are bolted directly to), 38 extrusions, 76 stampings, 3 hydroformed rails.

The C7 uses the world's largest single piece Hydroformed parts for the frame rails. Hydroforming is where sheets of aluminum are pressed into dies of complicated shapes using bladders filled with hydraulic fluid under a lot of pressure. The advantages of hydroforming over stamping are that the wall thickness stays constant so the part does not have weak thin areas. Hydroforming also allows for complicated compound shapes that stamping cannot reproduce. 

The C7 chassis also features 354 robotic spotwelds, 113 feet of structural adhesive (another industry leading figure, structural adhesive has advantages like a greater bond area to spread out loads, better shear strength, no heat affected zones that could weaken the structure like welding) and 37 feet of laser welds. The chassis uses a high-tech, stiff but light, nano carbon composite floor pan.

The C7 chassis also takes advantage of different properties of aluminum alloy for parts of its structure. The front crush structure uses super high strength 7000 series aluminum. The cast nodes use C356 alloy for more dimensional accuracy, and the rear crush structure uses a more ductile but still high strength 6000 series alloy.

With all this engineering, the C7 chassis is still light, weighing in at only 374 lbs. While the entire car weighs 3,440 lbs for a Z51 model like ours, which is about 40 lbs heavier than an equivalent C6 despite being much stiffer and slightly larger. If this seems heavy, it is only about 100-200 pounds more or less, heavier than a compact WRX or even a Civic.

 

The C7 powertrain has a front engine, rear drive orientation with a rear mounted transaxle instead of the typical transmission. This moves the heavy mass of the transmission and differential to the back of the car and is responsible for the cars near perfect weight distribution.

The engine and transaxle are connected by a rigid torque tube that contains the drive shaft. This prevents twisting from torque.  It also contributes to increasing the chassis bending stiffness. The C7 has a one-inch longer wheelbase than the C6.

 

The C7's suspension is very similar to the C6's in that it is an all aluminum unequal-length A-arm arrangement with a glass fiber composite transverse leaf spring. However, the geometry is slightly different and none of the parts interchange. The C7 has a one inch wider track width than the C6.

Although leaf spring sounds truck-like and crude, it has several compelling advantages over a coil spring. One, it cannot put a binding movement onto the shock shaft under compression like a coil over can. This binding can significantly contribute to a harsh ride and tire shock. This is the reason why many cars these days mount the spring independently of the damper.

Second, it puts the supporting weight task of the suspension low in the chassis to where it pushes up on the middle of the crossmember. This allows the front of the car to be built lighter as the shock towers or the shock supporting frame, in the case of the C7 doesn't have to hold up the weight of the car. 

Another interesting effect of the leaf spring is that it slightly couples the left and right side of the car so it acts like a small anti-sway bar. This enables the use of smaller and lighter bars than would normally be used. The ends of the leaf spring contain jack bolts that allow for the car to be lowered easily. The jack bolts can also be used to quickly and easily adjust the car's corner weights. 

The steering on the C7 is rack and pinion with electric power assist. The steering ratio is variable from 12 to 16.4 to one. The front control arms are cast aluminum and are hollow for lighter weight and to allow a larger cross section for improved stiffness. The front and rear subframes are cast hollow out of aluminum and are 25% lighter and 20% stiffer than the C6 subframes. The entire C7 is made of either aluminum or composite materials like a super expensive exotic!

 

Like the front suspension, the rear also has transverse composite leaf springs, hollow aluminum control arms and a hollow aluminum rear crossmember that is 25% stiffer and 9 pounds lighter than the C6 crossmember.  The rear suspension has the same geometry as the C6 although it has a one inch wider track. 

The rear transaxle on our Z51 has an electronically controlled limited slip differential that is one of the most important contributors to the handling improvements between the C6 and C7.  The differential can vary its torque transfer abilty from nearly open to close to fully locked with 1475 lb/ft of torque transfer abilty!

The differential controls torque transfer with an 11 millisecond response time using a hydraulically activated wet multidisc clutch.  The clutch is enabled with an external hydraulic pump and is integrated with the cars performance traction management system and stability control.

This allows the diff to be open and allow a sharp understeer free turn-in then seamlessly starts to add lock as the throttle comes down on corner exit to maximize corner exit traction. This way you can have the best of both worlds, no locked diff-induced understeer on turn in but with full traction on corner exit adjusted seamlessly so as to be transparent to the driver.

The Z51 transaxle has lower gear ratios in first through third gears for better low-speed acceleration.

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