7- & 8-post advanced road simulator systems are designed to extend the capability of 4-post rigs by superimposing a controllable pre-load on the vehicle chassis. This pre-load can be used to simulate the variable, but relatively low-frequency, effects of aerodynamic down-force on motor-sports and performance vehicles.

By offsetting the location of the down-force attachment, constant lateral forces associated with oval-track racing can also be simulated. Key to the successful simulation of down-force is having sufficient compliance within the connection linkage to deliver the force without significantly affecting the vehicle dynamics associated with the motion inputs from the main wheel-pan actuators.

Working in response a request from Williams F1 in the early 1990s Servotest was the first company to bring down-force simulation and actuation to market. The Servotest 'compliant link' was soon incorporated into 7-post rigs supplied to race-teams worldwide and remains the 'lowest-noise' mechanism on the market for this application.

While the most common configuration is the 7-post rig with three down-force actuators (one at the front and two at the back) some race teams prefer to use two pairs of down-force actuators, one at each end of the vehicle, this then becomes an 8-post rig. Although 8-post rigs are 'over-constrained' this configuration can still be controlled effectively by the Servotest Pulsar digital servo-controller.

The effective application of down-force typically requires additional signals to be measured relative to those used on a 4-post rig. These include wheel-pan load cells and vehicle body acceleration measurements made close to the down-force actuator attachment points. The wheel-pan load cell signals are then used to establish an even balance of loads between the vehicle wheels while the acceleration signals are integrated to provide a velocity signal that is used in a feed-forward control loop associated with the aero-loader control.

Although not essential for general 7-post rig use Servotest can also provide advanced control capabilities for 7-(& 8-)post rigs using our unique 'Sockets' feature. Sockets capability enables customer-developed Simulink® models to be run within the Pulsar real-time control loop. In race car applications this capability can be used, for example, to create maps of aerodynamic down-force values that are then used to determine the force levels to apply at each aero-loader at any given moment based upon other measured parameters such as vehicle ride-height. Since the detail and implementation of these models is entirely user-defined, teams can rest assured that this performance-critical capability and data remain entirely within their control, thereby protecting any competitive advantage gained.

As for 4-post rigs 7-/8-post rigs are almost always configured based upon the needs and requirement of each specific customer. Key specification points include vehicle mass, the 'unsprung' (moving) mass of the wheel and suspension components and the wheel-pan velocities and accelerations required. These will in-turn determine the actuator sizes, load and stroke ratings as well as the pressure and flow capabilities of the Hydraulic Power Supply.

Servotest has extensive experience in configuring, supplying and commissioning 7-(& 8-) post rigs to race teams and performance vehicle manufacturers worldwide. Our powerful DSP-based Pulsar multi-channel digital servo-control system has a full suite of capabilities for advanced ride simulation work. These include options for running either block-cycle loading or time-history road-load data by utilising the power of the EzFlow test sequencing software and ICS control/analysis capability. The advanced Sockets capability refered to above remains available and a virtual version of the ICS software is also available for predicting test system behaviour in advance of physical testing on the rig.

The Pulsar software user-interface is configured specifically for race car operation with schematic diagrams displaying key measurement data so that it can easily be related to its physical location on the vehicle. Additional dedicated user-interface screens are also available for specific tasks such as load-balancing.

For further information please download our Advanced Ride Simulation Systems brochure or contact us at our Egham office.

Please note that, as for any high-force dynamic test rig of this type, a suitable seismic foundation will also be required to ensure that the vibration and forces generated by the rig are not transmitted into the test facility or to adjacent equipment. While provision of this foundation typically remains a customer-facility responsibility early consultation with Servotest is recommended to provide general guidance with respect to the mass of this foundation.






Access Servotest information guides, brochure and videos.



Servotest Testing Systems Ltd
Unit 2, Alpha Way
Thorpe Industrial Estate
Egham Surrey
TW20 8RZ

Registered in England & Wales No: 6274550
Vat No. GB 910 1840 66.