If the tape measure is the racer's most handy tool, a kinematics and compliance rig is the
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.
The K&C rig works by attaching the framerails of the car to a central table. This table ma
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.
Interestingly, by taking precise measurements at the wheels, the rig can determine by math
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."
A K&C rig is often confused with a pull-down rig or even a seven-post shaker, but those on
Morse says they are commonly called on to help answer questions about whether or not the chassis simulation program a team is using is accurate, how the roll center migrates under different situations, and even the actual attitude of the car (versus static ride height) at different points on the racetrack. Morse says they often find things teams don't anticipate.
"We get a lot of 'We didn't expect that!'" he explains. "It can be anything from a worn ball joint, or chassis flex or something."
The reason, according to Morse, is that unlike measuring your setup in the shop, a K&C rig can position the car and suspension in any attitude it likely will see on the racetrack. That includes side-loading that comes from inertia as the car rolls through the turn. Unlike at-the-track testing, a computer-controlled rig is perfectly repeatable time after time. When at the track, variables such as temperature, condition of the track surface, engine condition, and even the driver's mood can affect the data you gather. A K&C rig removes those variables and can measure with amazing accuracy everything from how the contact patch moves as the car rolls through a turn to the friction in the suspension's pivot points.
Because of this, teams often discover the unexpected. One of the most helpful is the realization that the chassis is allowing unwanted compliance. Morse says that with the help of the rig, he and Simons are able to pinpoint unwanted flex down to a specific weld. They do this by using a set of sensors attached to points on the car that indicate if those points move relative to the rest of the car. Once they locate the general area of flex, or compliance, the team keeps focusing on it until they can tell you whether it's a bad weld, a bushing, or something else. Once all compliance issues are found and taken care of, Morse says race teams find that setup changes and adjustments become much more predictable.
Morse says that one of the advantages of using a facility like Morse Measurements is that
Another component a K&C rig provides is help determining which chassis changes will maximize overall traction. On the racetrack, having a balanced race car that is easy to drive becomes as important as outright speed. A car that drives well exhibits good balance. In other words, the front and rear tires offer equal amounts of grip so that the car is neither loose nor tight. Unfortunately, in order to give a driver a balanced car, crew chiefs too often elect to reduce the traction of a set of tires-either the fronts or the rears-in order to balance the traction between the front and back of the car. Morse says that a K&C rig helps identify changes that will keep a car balanced under different conditions while also maximizing traction at all four corners.
Today, kinematics and compliance testing is still in its relative infancy when it comes to stock car racing, but rest assured that its popularity will soon be growing as teams discover ways to use it. Of course, wind tunnels were rarely considered a useful tool for races little more than a decade ago, and look where tunnel usage is now. The most forward-thinking crew chiefs and race teams will look to K&C testing to see if it gives them a leg up on the competition. The success or failure of these vanguard teams in the next few seasons will determine if K&C testing will become as accepted in racing as your trusted caster/camber gauge.
A remote steering actuator demonstrates how traction changes as the driver changes steerin
The load cells under each wheel float horizontally to eliminate binding and show you exact
Morse Measurements was formed in 2003, but it took the staff (from left: Phil Morse, Bob S