To find out why, we talked to Erich Heuschele, the engineer responsible for vehicle integration at Chrysler's SRT performance division, the people behind the new Viper.
Today, engineering teams do the preliminary work such as designing suspension geometry and specifying shock valving on computer simulations, which help them to get the basic setup close to perfect. Engineers plug into the vehicle's CAN bus to gather information on steering angle, vehicle yaw, pedal application, and more. They put instruments on the axles to measure the application of torque and to directly gather wheel speed. "We've even mounted cameras in wheel wells to see if we have a toe compliance problem," he says.
To diagnose especially frustrating problems, engineers can use a suspension parameter measurement machine (SPMM), which uses hydraulic actuators to slowly cycle the suspension through its range of motion on a stationary car mounted to a platform. Using all of these tools can reveal irregularities introduced from unexpected sources, such as unintended toe changes that steer a wheel in or outward when the suspension compresses.
But computer simulations have their limits. For example, "what is not simulated well is shock tuning and at-the-limit handling," Heuschele says. So, even with all that data in place from this battery of instruments, the one gauge that engineers rely on the most is the test driver, he says. "The best transducer in a car is still a human, because there are more channels of data."
SRT likes to test cars with people in them under a wide variety of conditions. The team has a network of challenging public roads its uses to sort out cars in addition to its own proving ground circuits and tracks where cars like the Viper can encounter more of the circumstances customers will find in their travels. That includes the hot- and cold-weather test sites in the desert and up north along with mountain passes to gauge handling prowess.
In these conditions, Heuschele says, human input is particularly important because of the need to tune suspension for the conditions commonly encountered, rather than the rare-but-dangerous conditions. "You don't tune cars for one bump," Heuschele says. "If your tune for one bump you miss for ten million bumps." (Such a focus on a worst-case-scenario rather than everyday conditions can lead to the kinds of cars for which domestic carmakers have long been criticized by driving enthusiasts: ones that feel soft and isolated most of the time but that can withstand Michigan's worst potholes with aplomb.)
That means putting real people in the car on real roads, which is why Heuschele and SRT don't just do their work at a famed racetrack like the Nürburgring, where even dull crossovers are putting in lap times these days. "You can't just tune at the proving grounds. You have to go drive the cars around in the real world," he says. "I would need a minimum of month at the Ring. We never tested the Viper ACR at the Ring. We go there, set the record, and leave."
He prefers to have human drivers test cars under real conditionsboth inside and outside of the car. Having a second person in the car, for example, can even be helpful. "If I'm shock tuning, I'd love to have a fat guy sitting in the passenger seat," Heuschele says. "You can tell how decoupled his body is from the car's motion."
But it is the human behind the wheel who provides the real value. He or she is the one who can report that the car feels weird over a particular sort of road when the computer says everything is fine. That's when the team breaks out all the tools of the tradethe sensors and camerasto locate the source of the strange feeling. Machines can help diagnose the problem, then. But cars are made for humans, and it still takes a human to say how a great car should ride.