Praxis System Q&A
Apr 29, 2004
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Q: What is included in the Praxis™ system?
A: The Praxis system includes all components necessary to convert your vehicle. The system has been designed to be application specific, in order to ensure proper fitment and avoid performance and installation issues often encountered with “generic” aftermarket products. Praxis products are properly packaged to avoid damage during shipping and include a comprehensive set of instructions to ease installation. A comprehensive list of system components is provided below:
3-way adjustable, inverted-monotube struts (4)
Multi-Rate air springs (4)
Air compressor
Air dryer
Trunk mounted, auxiliary air reservoir
Valve block
ECU
Multi-axis accelerometer
Height sensors (4)
Wiring harness (pre-assembled with fuses and relays)
Cockpit control module
Brackets for air reservoir, compressor, ECU, valve block, and height sensors
Air plumbing
Installation hardware
Detailed instructions
Q: How does the Praxis system differ from other air suspensions?
A: Air suspensions have established applications in the hot-rod and low-rider aftermarket, in factory-produced luxury vehicles and commercial trucks. These existing applications often foster a stereotypical image that air suspensions are used purely for ride-comfort, load-carrying, or whiz-bang car show demonstrations. However, it is important to realize that air suspensions have application in all areas of the automotive world. As the original-equipment marketplace becomes more technologically competitive, automobile manufacturers pursue advanced methods to optimize chassis dynamics and ride comfort.
When properly engineered, air suspension systems can deliver luxury ride and sports car cornering. Recent products like the BMW 745, Mercedes E500, Porsche Cayenne and BMW X-5 all use air springs to achieve exemplary performance. Praxis has developed an aftermarket air suspension system that, for the first time, uses air spring technology to enhance the sporting performance envelope of the vehicle while avoiding the day-to-day compromises often encountered with existing aftermarket products.
Q: How does an air spring differ from a coil spring?
A: The visual difference is obvious. The operating principles are different. One produces a spring force by stressing a steel rod, while the other produces the same force by compressing a trapped volume of air. Functionally, there is no difference. The vehicle chassis only interacts with a spring force … it does not care whether that force originates from a steel spring or from an air spring. The air spring differs because we can control its properties. We can change its height (and the height of the vehicle) by controlling the pressure within the air spring. We can also change the spring rate in a dual-rate system by altering the volume of air contained inside the spring. To accomplish the same feat with a coil spring requires physically changing parts … more parts, more time, more cost.
Q: How does the user change operating modes in the Praxis system?
A: Praxis allows the driver to select the height, spring-rate and damping for whatever driving adventure lies ahead. There are no coil-springs to change and no spanners to carry, because the spring-rate and ride-height is controlled by air. It’s as easy as touching a button and turning a knob. First, select one of three programmed ride-heights and spring-rate levels with a simple push of a cockpit-mounted button. Then adjust damping by turning the adjuster conveniently located on each strut-unit. Touring mode, Sport mode or Track mode ... you control the level of performance.
Q: Does raising and lowering the vehicle affect wheel alignment?
A: It is well known that toe and camber change as ride height is altered. Our alignment specification (different than the factory specification) will allow daily use of Touring and Sport modes without affecting tire wear. When the car enters theTrack mode, the camber becomes more aggressive (negative) ... this is good for lap times and will not produce undesirable wear considering the race-circuit environment. Randomly choosing an aggressive camber angle without regard for toe setting or other suspension characteristics usually results in rapid and irregular tire wear. Bridgestone technology has enabled us to use state-of-the-art methods of predicting tire wear, to optimize the alignment setting to balance both handling and tread life. You will not have to realign the car when you change ride heights. You will need a one-time alignment when the system is installed.
Q: Why does the Praxis system include an accelerometer?
A: Since the Praxis system was designed specifically with the performance enthusiast in mind, it was necessary to produce a product that performed flawlessly on a racing circuit. The accelerometer serves this function by providing the ECU with information about how hard the vehicle is being driven. In turn, the ECU can make informed decisions about when to add or remove air from an individual spring. The presence of the accelerometer allows the ECU to intelligently decide whether a suspension motion is originating from forces that demand air movement (i.e. adding cargo or changing operating modes) or from forces that do not warrant movement (i.e. high-g cornering or skid-pad testing).
Q: How can the Praxis system automatically corner-weight the vehicle?
A: Because the Praxis ECU and valve-block can control airflow to, from, and between the air-springs mounted at individual wheel-positions, we have been able to develop a control sequence that automatically re-distributes air between springs during a height-change. This re-distribution results in balanced diagonal weights, and a car that handles symmetrically in right and left turns.
Q: How much does the system weigh?
A: The system adds approximately 30 pounds to the weight of the vehicle. The increased weight comes mostly from the air-supply system (compressor, air tank, valve-block assembly) and is equally distributed between the front and rear of the vehicle.
Q: How long will it take to install the system?
A: Installation of the Praxis system is somewhat more complex than the typical strut installation because of the air-line plumbing and electrical wiring that must be routed through the interior of the vehicle. We have simplified the installation by providing fully assembled strut units that can simply be bolted in place and a wiring harness that is fully pre-assembled. All brackets are application specific, so no fitting, adjusting, drilling, welding or soldering is necessary. Fully detailed instructions will guide a moderately accomplished amateur through the installation process in eight to ten hours. No special tools are required, but the vehicle will require a suspension alignment after the installation is complete.
Q: Will the system adjust as my car is raised on a lift for servicing?
A: No. A service switch is included as part of the system. This switch deactivates the system and allows for servicing on a lift or changing a tire.
Q: Does Praxis have certified installers?
A: At this point, we have not established a certified installer base. It will be the responsibility of the purchaser to install or contract for installation of the product.
Q: For what vehicles is Praxis currently available?
A: The Praxis system is now available for the Subaru WRX. Praxis for the BMW 3-Series (1999-present, coupes, sedans and wagons) will be available in June 2004, and for Ford Mustangs (1994-2004) in third quarter 2004.
Q: How much does the Praxis system cost?
A: The Praxis system for the Subaru WRX has a Manufacturer’s Suggested Retail Price (MSRP) of $3,695. Pricing for the BMW and Ford Mustang will be announced nearer those systems’ availability dates.
Q: Where can I purchase the Praxis system?
A: The Praxis system is available for purchase at The Tire Rack, (800) 428-8355 or visit the website at www.tirerack.com.
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