Kinematics and Compliance Rigs - The Nuclear Yardstick

Racers spend hours upon hours trying to understand exactly how a suspension works under different conditions so they can maximize a car's traction around the racetrack. No matter if you are racing Street Stocks at your local bullring or if you're the crew chief for a multimillion-dollar Nextel Cup team, the story is the same: Once you begin to understand the chassis system, you can then add a measurable component and realize it changes everything.

Let's consider the most basic scenario as an example. One of the first measurements a new racer will track is front-wheel camber. Of course, camber at ride height is very limited information, so the racer begins making a camber sweep, tracking changes at different points of suspension movement. That sounds good, but once you change track width, caster, antidive, bumpsteer, or even the ball joints, all that goes out the window.

Until now, there were three major ways to gather suspension information: measurements made in the shop; information gathered during on-track test sessions; and chassis simulation programs. All three methods are useful, but all three also have their weaknesses. Now, a fourth method is becoming more and more available and adding another layer of information race teams can access.

The new method is a system of measuring how the wheels move as the suspension is actuated. It uses a complicated, computer-controlled rig that connects to a race car's framerails and moves it in motions similar to what the car would see on a racetrack. The four wheels sit on pads that measure pressure. The pads do not move up and down, but can either be locked in position or allowed to "float" or move to measure changes in wheelbase and track width as the suspension is actuated. The pads are so sensitive that they can actually track the movement of not only the tire but also the center of the footprint of each tire.

A setup like this is known as a K&C rig, which stands for Kinematics and Compliance. Kinematics describes how the suspension moves when it is activated. Compliance is measuring how the suspension flexes or moves in ways not necessarily intended under load. Compliance issues can include anything from soft bushing flex, to slop caused by worn ball joints, to flex allowed by flimsy or undersized suspension components. Amazingly, a quality K&C rig operated by a savvy technician can tell the difference between normal suspension movement and compliance issues.

That all sounds good, but up until recently, K&C rigs were the exclusive domain of the big guys-mega corporations such as the automobile and tire manufacturers. Not long ago, however, Phil Morse and Bob Simons, two automotive engineers, made a K&C rig available to the masses. The rig, which was constructed in Britain and is only the eighth of its type ever made, went online in October 2005 in the Morse Measurements facility in Salisbury, North Carolina. Currently, it is the only privately owned K&C rig of any type available for public use in North America.

Morse says there is a lot a team can learn from a K&C rig. Today, most of Morse Measurements' racing clientele is comprised of Nextel Cup teams, but he believes more and more lower-level teams will come to depend on the services they provide as well.

"As a private company, we aren't tied to any manufacturer, so we can help any team," he says. "We have racing backgrounds, and unlike K&C rigs owned by the manufacturers, many of our tests are designed around what the race teams are looking for. Many teams are still learning about what types of information they can get from a session on a K&C rig, but when you come here, the fee for the use of the rig also gets you the services of two engineers for free. We are very careful about not disclosing to another team what one team has learned, but we can help you interpret and use the information you collect."