New Cadillac Sedan Put Through The 'Ring'
New Cadillac Sedan Put Through The 'Ring'
GM engineers rigorously test the new CTS sports sedan at Germany's legendary Nürburgring
Nürburg, Germany. - It was clear from the start of development that the new Cadillac CTS would have to be different. The goal was to produce a true sports sedan with a European driving feel that would meet the lofty expectations of customers in North America, one that would represent the global brand Cadillac is poised to become. One way that General Motors' engineering and development team set about creating the CTS was to test it on the most challenging race circuit in the world, Germany's famed Nürburgring.
The ultimate proving ground for vehicle dynamics Since it was completed in 1927, the 12.8-mile Nürburgring has challenged drivers of literally all skill levels. Altitude changes range nearly 1000 feet. The 'Ring has 177 corners, and in between them is every conceivable combination of radius, camber and gradient. No other track in the world places such extreme demands on a vehicle's suspension, brakes and powertrain. Today, anybody with a car, a license and about $10 can run hot laps where the likes of Fangio once ran. That is, unless a scheduled manufacturer test session has closed the 'Ring, where some of the world's finest vehicles are regularly tested in development.
To hone the CTS into a true world-class sports sedan, GM and Cadillac decided to benchmark the best, and test where they test.
Cadillac drew on Opel AG's years of testing experience at the Nürburgring when putting together its CTS development team three years ago. Lead CTS development engineer Ken Morris was joined by Opel development engineer Michael Harter to fine-tune the CTS at the 'Ring, on Germany's autobahn and other test sites throughout North America.
"Michael explained to us how critical it was that we do development work in Germany," said Morris. "When we saw the demands that the Nürburgring places on the cars, and the level of commitment from Audi, BMW, Mercedes and Porsche to test their cars to the limit, that's when we knew without question that CTS would have to do the same thing. For a minimum of six weeks per year for the past three years, we did exactly that."
Ride around the 'Ring
"In just one lap of the 'Ring, you experience the entire gamut of cornering speeds, lateral forces, braking conditions and vertical inputs," said Morris. "You're forced to brake in situations where you might not otherwise, to change throttle positions or steering inputs at either high or low speeds and, in other cases, to take corners at very aggressive speeds. The 'Ring provides a relatively controlled environment with a repeatable series of events that help make sure a car is capable in every situation."
The CTS development team gained a wealth of knowledge from the Nürburgring. Nearly every system on the car was painstakingly tested, evaluated, adjusted, tweaked, retested, reevaluated, readjusted and retweaked time and again-until everything met the team's needs, wants and expectations. Among the findings:
- Brakes: As a direct result of the high-speed testing at the Nürburgring, the brakes on the CTS have more of a linear brake pedal feel than most GM vehicles in recent memory. Toe changes and the pitch of the car during aggressive braking were also tested and refined thoroughly.
- Manual transmission: Like the car's rear-wheel-drive architecture, the presence of the Getrag five-speed manual transmission is a key element in making the CTS a true driver's car. Placement of the clutch, brake and throttle pedals was optimized for heel-and-toe operation, an important consideration for any performance vehicle. Rigorous testing at the Nürburgring allowed engineers to find the right throttle progression and clutch engagement point.
- Gear ratios: The gear ratios in the manual transmission were matched to the power output of the 3.2-liter V6. The spacing between the ratios also was carefully determined to keep the rpm's in the power band during upshifting. Various iterations of ratios and gear spacing were tested at the Nürburgring until the ideal combinations were reached.
- Automatic transmission: The 5L40-E Hydra-Matic five-speed automatic transmission, also used in the BMW 5 Series, is GM's first production five-speed automatic. The development team ran repeated tests to tune the automatic to match the performance of the manual as much as possible. Electronic engine braking in all five gears, another GM first, was also evaluated thoroughly and calibrated as a result of the testing. The 5L40-E's performance shift mode settings and adaptive shift patterns were configured to optimize the transmission's capabilities and anticipate the driver's needs.
- Steering: The steering inputs needed to successfully navigate the Nürburgring translate to extremely precise control and superior steering feel on the freeway. Working closely with steering supplier TRW, the CTS team developed the rack-and-pinion system to provide the feedback and control appropriate for a German-tested sports sedan.
- Ride and handling: One of the keys to building any performance car is striking the correct balance between a smooth ride and precise handling. Through nearly 1 million durability miles (including the 'Ring tests) and more than 200 non-saleable test models, the CTS team has optimized ride and handling, and created a vehicle that behaves with poise and predictability. The team worked on-site at the 'Ring with supplier Sachs Automotive to make immediate modifications to the shock absorber tuning to find the right combination of damping. They tested more than 40 iterations of the complex multi-link rear suspension, changing geometry points and locations of suspension components before the best setup was determined.
###
