What is K&C Testing

K&C v. 7-post Shaker

The AB Dynamics K&C test machine at Morse Measurements is not a 7-post shaker rig. We don’t “shake” cars or report results in the frequency domain. We don’t use hydraulics, and the results are not difficult to understand.

For racing applications, 7-post shaker rigs are used primarily for tuning suspension dampers. The typical goals are to  minimize contact patch load variation over known road/track profiles, and improve vehicle pitch behavior for improved aerodynamics. Since shaker rigs apply only vertical loads (no braking, cornering, or tractive loads), they cannot measure the jacking force effects resulting from roll centers, anti-dive, and anti-squat characteristics. Further, no measurement is made of toe, camber, or wheel center motion, so suspension geometry and stiffness characteristics cannot be evaluated.

K&C rigs are used for tuning everything else in the suspension, beyond the dampers. The typical goals are to optimize the loaded and unloaded suspension geometry over known road/track profiles, and maximize the mechanical grip of each tire by optimizing longitudinal and lateral weight transfer.

K&C testing and 7-post testing actually compliment each other in many ways because K&C tests capture information that is just not available from shaker rig testing.

 

Key Suspension Items

K&C

7-post

Apply braking, cornering, and traction forces at all tires

Yes!

No

Simulate true trim with steer, tire loads, roll, pitch, & heave

Yes!

No

Measure ride and roll rates with scrub relief

Yes!

No

Find roll center heights, instant centers, and jacking ratios

Yes!

No

Measure toe, camber, and caster (geometry and stiffness)

Yes!

No

Locate center of pressure for each tire contact patch

Yes!

No

Identify Ackermann and loaded steering geometry

Yes!

No

Measure steering system friction & stiffness characteristics

Yes!

No

Measure suspension friction levels

Yes!

No

Measure local chassis deflections from real tire loads

Yes!

No

 

 

K&C and 7-post testing can be used together to create comprehensive tuning maps for a vehicle suspension, particularly for pitch and aerodynamic stability. Be cautioned, however: 7-post rigs cannot introduce cornering or braking/tractive loads. Without the inclusion of jacking forces, 7-post rig-tested tire loads will not be correct. (This is dicussed in more detail and illustrated with some examples on the page comparing K&C vs. Pull-Down rigs.)