5 out of 5
Within the Special Vehicles section of Bridgestone/Firestone is a small group of very taleneted men. They devised a plan to build the
best adjustable suspension that could adapt to all types of use. From daily traffic street driving to across the threshold at the racetrack.
After years of research and testing and access to the billion dollar development and engineering assets of Bridgestone, the result is the Praxis
Advanced Suspension System.
The system consists of 4 bladders or "air springs" specifically designed for the vehicle, fully adjustable shocks, height sensors, cockpit control unit, Electronic Command Unit (the brains), an acclerometer, a fully assembled air handling unit (air compressor, dryer, and valve block), air storage tank, and a complete electrical harness. In co-operation with H&R, they designed proprietary struts for use in the front suspension. By controlling the effective air volume in each of the bladders, the amount of surface area contacting the strut changes. Praxis has designed an "air spring" that gets actually gets stiffer as you lower the air volume and therefore the ride height. It is a miracle of science, I say!
Price for the system is $3795 (as of 3-26-2005 from TIRERACK.COM).
PRAXIS ADVANCED SUSPENSION
I honestly didn't know what to expect from this suspension originally . I first saw it on a display at SEMA 2003 for the Subaru WRX. I talked with the gentlemen from Bridgestone and got as much information as I could gather. Turns out it was being released for the E46 3 Series the following year (2004). I got contact information and was able to get my hands on one of the first production units for the BMW. It came in 2 big boxes, nicely packaged. I couldn't
wait. I opened everything to get an idea of what I was getting into. The entire system is beautifully crafted and everything is labelled to make
installation a lot easier.
See the Installation page HERE.
Once I got the system installed and operating, I took it out and drove the heck out of it. WOW! The differences in the settings are VERY noticable and
each provides exactly what the setting name implies:
TOURING is great for the long drives out of town or if you spend a lot of time on bad roads. It
sits high as non-sport stock, which was odd for me at first. My BMWs have always come with Sport suspensions so to see that much wheel gap was strange
at first, but the ride is smooth as silk! It is also extremely helpful in getting over that nasty speedbump or over those evil driveway angles. A simple push of the button into Touring and you have all the clearance you need. Simply outstanding.
Next down is SPORT mode. Night and day difference from Touring. We drop an inch and stiffen our spring rates by about 40%. The change from Touring only takes about 6 seconds. The car becomes tighter, more responsive, and snappier in the turns. It is just all around fun! It sits a little lower than my ZHP came stock, but the ride is better. I was suprised how stiff the ZHP stock suspension was. This Praxis made it all feel great. I drive it all the time in Sport mode now.
Another push of the down button brings us to TRACK mode. Another half inch down and the spring rates increase again by about another 30%. This mode is not recommended on the street as the camber is in the high -2s and is truely meant for the road course. It will simply wear out your street tires early. But when you get it to the racetrack, this thing is on RAILS. It is an exhilirating experience to not feel the car dive or lean into corners, even through demanding chicanes and esses. It just stays planted and goes where you point it.
In every mode, the car auto-levels to acheive the selected program height. It doens't matter if you drive alone, with passengers, or full of luggage, the system will always set the car to the height stored in memory. No more bottoming out because all of your friends want to go with you. It is always ready to go. To make the car even better, you can setup the system with the car resting on corner scales. Precisely corner-balance it one time and never again!
Other nice features of the system include its flexibility. The Praxis factory recommended height/dampener settings are set up to provide a balance or performance, longevity, control, and comfort. These settings are more than adequate for everyone, including myself. However, since you choose the heights for each setting during the install, you could perhaps set Touring to a sport height, drop Sport mode for car shows, then leave Track slammed barely above the bump stops for the autocross or road course for example. Your only limitation is that each setting HAS to be progressively lower than the one before. Sport has to be lower than Touring, and Track lower than Sport. It is all up to you, just remember that extremely low ride heights build in excessive negative camber, so it is not for use on the street. By the way, you can SLAM this thing. It is NOT drivable if you do this, but you can manually let the air out and set the car down on the bump stops. I have 18" wheels and I can make them disappear into the fenders. If you are looking for that extra edge at a competition, this could be it. Then, when you are ready to leave, push a button, back up it goes, and drive it away at the shock of onlookers.
Additionally, the air storage tank keeps about 140psi in it at all times. Since the unused tank end fits a standard 3/8" NPT air fitting, you could technically put a press-on fitting there and have a coiled air supply hose in your trunk for use at the track or if you get a flat. On board air! This is an available option for purchase through Tirerack if you so desire.
Overall, I absolutely LOVE this suspension! If I had to come up with a complaint, it would be having to manually change the shocks to make the best use of each height setting. But to be honest, I keep it in Sport all the time only kicking it up to Touring to clear obstacles. When it goes to the track, I don't mind taking a few minutes to climb under and set the shocks to Track dampening. The benefits far outweigh any possible complaint I could come up with. It is an expensive system in comparison other suspensions, but it does so much more, it is worth every penny!
For the best suspension you can get, I would highly recommend the Praxis! Tell them I sent ya!
So, I put the car on corner scales today to check the Praxis and setup a buddy's Praxis on his M3 and found some interesting numbers. In all modes, the front/back and left/right weights are almost a perfect 50/50 within .5%. Very nice on Praxis's part.
However, the cross weights were a different story, over 56% difference, with the axles being opposite by over 300lbs. Around 700# LF and RR, over 1000# RF and LR. Now, most people wouldn't notice that, but I wanted it perfect and adjusted Sport mode to 50/50/50 (right at 850# at each corner). It handles even better, but at the cost of not looking symmetrical to the *very* detailed bystander eye. It is about 3/8" higher on the left side than the right. Kinda like how BMW suspensions come stock; higher on the driver's side.
I don't mind it as the handling is extremely neutral and I still have Touring and Track set to Praxis spec.