What a 7 Post Shaker Rig Can (and Can’t) Do

What is a Shaker Rig (or 7 Post)?

A shaker rig (or 7 post rig) is a type of suspension test machine that applies vertical loads to the vehicle at a high frequencies in order to analyze vehicle response, typically across a specific road or track profile.

How Is a 7 Post Shaker Rig Used?

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.

Shaker Rig Testing vs. K&C Testing

K&C testing is used to tune the vast majority of a vehicle’s dynamic fingerprint. A K&C rig doesn’t “shake” cars or report results in the frequency domain and the results are not difficult to understand. 

Use of shaker rig (7 post) testing

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.

Shaker Testing AND K&C Testing

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

 

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 discussed in more detail and illustrated with some examples on the page comparing K&C vs. Pull-Down rigs.

What is a Shaker Rig (or 7 Post)?

A shaker rig (or 7 post rig) is a type of suspension test machine that applies vertical loads to the vehicle at a high frequencies in order to analyze vehicle response, typically across a specific road or track profile.

How Is a 7 Post Shaker Rig Used?

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.

Shaker Rig Testing vs. K&C Testing

K&C testing is used to tune the vast majority of a vehicle’s dynamic fingerprint. A K&C rig doesn’t “shake” cars or report results in the frequency domain and the results are not difficult to understand. 

Use of shaker rig (7 post) testing

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.

Shaker Testing AND K&C Testing

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

Key Suspension Items K&C 7-post
Apply braking, cornering, and traction forces at all tiresYes!No
Simulate true trim with steer, tire loads, roll, pitch, & heaveYes!No
Measure ride and roll rates with scrub reliefYes!No
Find roll center heights, instant centers, and jacking ratiosYes!No
Measure toe, camber, and caster (geometry and stiffness)Yes!No
Locate center of pressure for each tire contact patchYes!No
Identify Ackermann and loaded steering geometryYes!No
Measure steering system friction & stiffness characteristicsYes!No
Measure suspension friction levelsYes!No
Measure local chassis deflections from real tire loadsYes!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 discussed in more detail and illustrated with some examples on the page comparing K&C vs. Pull-Down rigs.

 

There are several critical tools to develop and improve racecar performance. These include shaker rigs, wind tunnels, and kinematics & compliance (K&C) testing. Everyone needs K&C testing in their vehicle development program to either verify suspension information from the factory or assure quality in setup specifications. It is difficult, time consuming, expensive, and error prone to make K&C measurements on your own.

Morse Measurements provides cost effective, one stop shopping for a comprehensive K&C test session in less than a day. In a short time, you get all of the suspension kinematics as well as stiffness under load. K&C testing at Morse Measurements allows you to apply realistic combined loading which provides insight into what is really happening when on track.

The Morse Measurements support staff is responsive and helpful. At the end of the day I walk out knowing several key balance conditions – i.e. the rear has an oversteer tendency under vertical loading. Once back at the office, Morse Measurements has provided the tools to look further into the issue and attempt to resolve it plus understand any secondary parameters or conditions.

Joe La Joie

Race & Development Engineer, Vehicle Dynamics Performance, Inc.

Call Now: 704.638.6515

Call Now:
704.638.6515

      

1163 Speedway Blvd.,
Salisbury, NC 28146

Phone: 704.638.6515
Fax: 704.638.6516
Info@MorseMeasurements.com

1163 Speedway Blvd.,
Salisbury, NC 28146

Phone: 704.638.6515
Fax: 704.638.6516
Info@MorseMeasurements.com

© 2019 Morse Measurements | Powered by Miller Davis

 

      

1163 Speedway Blvd., Salisbury, NC 28146

Phone: 704.638.6515
Fax: 704.638.6516
Info@MorseMeasurements.com