MORE THAN PERFORMANCE: CORVETTE ZR1’S CHASSIS AND SUSPENSION DELIVER A CONFIDENT, COMFORTABLE DRIVING EXPERIENCE
Source: GM Media
December 20, 2007
DETROIT – Its supercharged engine twists out more than 600 horsepower and nearly 600 lb.-ft. of torque. Its racing-inspired dual-disc clutch channels that power to a set of massive, 20-inch by 12-inch rear wheels, helping push the ZR1 to more than 200 mph (320 km/h). It also corners with the grip of a hungry Kodiak bear – delivering more than 1g of lateral acceleration – and stops with exceptional immediacy.
Yet for all its astounding performance attributes, the 2009 Corvette ZR1 has a refined driving experience that makes it a daily-driveable supercar.
“The ZR1 is a car anyone can drive confidently and comfortably,” said Tom Wallace, vehicle line executive. “From the very beginning, refinement, balance and compliance were targets that were as important as the car’s maximum performance.”
More than simply scaling wheel, tire and brake sizes to match the powertrain’s output, the ZR1’s engineers harmonized the chassis and suspension components to deliver a ride quality and driving experience that is unmatched by most supercar competitors. Enabling elements include standard Magnetic Selective Ride Control and new, Michelin Pilot Sport 2 tires that were developed specifically for the car.
“The ZR1 corners better than the Z06, but has ride compliance more like the base coupe,” said Tadge Juechter, Corvette chief engineer. “Every element from the stabilizer-bar diameters to the composition of the tires was carefully matched to deliver a balanced driving experience – it’s a supercar that doesn’t sacrifice ride quality for performance.”
Stopping power is derived from a carbon-ceramic-based brake system that is lightweight, heat resistant and wear resistant. While delivering braking performance similar to a racecar, it helps reduce the unsprung mass that the ZR1 would have accrued through the use of similarly sized cast iron brake rotors.
“It wasn’t enough to achieve the braking requirements commensurate with the car’s performance – we needed to find a solution that minimized the impact on the car’s balanced feel,” said Juechter. “A larger brake package generally means more weight, but the carbon-ceramic rotors deliver excellent performance while also minimizing unsprung weight.”
The ZR1 has an aluminum structure for optimum stiffness and low mass. It is the same structure used on the Z06, but with specific body panels and drivetrain components mounted to it.
The chassis is constructed with perimeter rails made of strong, single-piece hydroformed aluminum members featuring cast suspension nodes. Other castings, stampings and extrusions are combined into the structure with state-of-the-art manufacturing technologies. Advanced structural composites featuring carbon-fiber are bonded to the aluminum structure. The passenger compartment floors, for example, combine carbon-fiber skins with an ultra-lightweight balsa wood core.
Like the Z06, the ZR1 has a magnesium cradle that serves as the attachment point for the engine and some front suspension components, with the new LS9 engine sitting slightly lower in the chassis than the Z06’s LS7 engine. Magnesium is lighter than aluminum yet incredibly strong. The magnesium cradle helps improve the front-to-rear weight distribution, as do the carbon-fiber front fenders, hood and wheelhouses.
To optimize the weight balance, the battery is located in the rear cargo area, behind the right rear wheel.
Suspension tuning and Magnetic Selective Ride Control
The ZR1 retains the 105.7-inch (2,686-mm) wheelbase of other Corvette models, as well as the short-long arm suspension and transverse spring design, but it rides on all-new, wider wheels and tires, stops with carbon-ceramic brakes and features specific spring and stabilizer bar rates – the largest-diameter stabilizer bars available on a Corvette. Also, the axle half-shafts are angled more horizontally to align with the different geometry created by the ZR1’s larger-diameter and wider rear wheels.
Magnetic Selective Ride Control (MSRC) is standard and tuned specifically for the ZR1. It is a real-time damping system that replaces conventional mechanical-valve shocks with electronically controlled shocks filled with a synthetic fluid containing minute iron particles. Under the presence of magnetic charge, the iron particles align to provide damping resistance almost instantly.
MSRC “reads” the road in 1-milisecond intervals (a thousand times per second), making it the world’s fastest-reacting damping system. Its ability to deliver a compliant ride with nearly instantaneous damping adjustments enabled engineers to develop a surprisingly supple ride quality in a supercar that still delivers cornering grip of more than 1g.
“The damping control of MSRC allowed for front and rear springs that have a slightly lower rate than the Z06, which enhances the car’s ride quality,” said Juechter.
From a high-performance perspective, Magnetic Selective Ride Control helps the rear axle remain planted during launch for smooth, hop-free acceleration. It also helps suppress axle movement when cornering on broken or uneven pavement.
With cornering capability greater than the Z06, the ZR1’s powertrain was upgraded with a higher-capacity oil pump and larger-capacity oil reservoir. This ensures optimal oil pressure during the highest-load driving maneuvers.
The ZR1 comes standard with carbon-ceramic brake rotors and large-capacity calipers at all for corners. The exotic carbon-ceramic rotors are made of a carbon-fiber-reinforced ceramic silicon carbide material, which offers low mass and exceptional resistance to wear and heat.
The vented and cross-drilled rotors on the ZR1 measure 15.5 inches (394 mm) in diameter in the front and 15 inches (380 mm) in diameter in the rear – making them among the largest carbon-ceramic rotors available on any production vehicle. And while large in size, they are low in mass, saving approximately 11 pounds (5 kg) per corner over comparably sized cast iron rotors.
The rotors are acted upon by six-piston front calipers and four-piston rear calipers, each painted a ZR1-exclusive blue. The front pads are equivalent in size to the largest on any production car with a single-pad design, measuring 148 sq. cm. in surface area – double that of the Corvette Z06’s 70-sq.-cm. front pads.
Braking performance of the ZR1 is nothing short of phenomenal, with the carbon-ceramic rotors and large calipers combining to provide exceptionally short, fade-free stopping during high-performance driving. The composition and durability of the non-metallic carbon-ceramic materials means the rotors should never show any corrosion or require replacement for the life of the vehicle, when used in normal driving.
A new, Bosch brake-apply system is standard and includes the brake master cylinder, booster and ABS control module. It is tuned specifically for the ZR1 and is not shared with other Corvette models. The system works with Magnetic Selective Ride Control to deliver a very competent and intuitive active handling system – complete with a Competitive Driving mode.
Michelin Pilot Sport 2 tires
The ZR1 rides on Michelin Pilot Sport 2 (PS2) tires, measuring P285/30ZR19 in front and P335/25ZR20 in the rear. And while the PS2 tire is familiar with enthusiasts, those on the ZR1 were engineered specifically for the car.
“We didn’t merely specify a set of off-the-shelf PS2s for the ZR1,” said Juechter. “Michelin’s engineers worked with GM to develop tires for the car that took into account factors such as the ZR1’s performance goals, expected horsepower, curb weight, weight distribution, aerodynamic downforce, top speed and more. The construction of these tires is unique to the ZR1.”
To maximize weight savings, there is no spare tire in the ZR1; the PS2 tires feature Michelin’s ZP technology and can be driven for a short distance with zero pressure until servicing can be attained.
The ZR1 rides on exclusive 20-spoke alloy rims that measure 19 inches by 10 inches in the front and 20 inches by 12 inches in the rear, making them the largest ever offered on a Corvette. Their design was inspired by the multi-spoke racing wheels used on Corvette C6R racecars, which enhance the strength of the wheel at the rim. A bright, Sterling Silver paint finish is standard and a chrome version is optional.
The wheels, while slightly larger in mass than the smaller wheels of the Z06, were developed to be as lightweight as possible, minimizing the ZR1’s unsprung mass.