ST S4 front sway bar on my S5
 

Just some personal experience from installing the Suspension Techniques S4 front 1-1/8" sway bar on my S5 GXL. I have had some fitment issues, but one thing for sure - it keeps the front end flat in the corners!

When I installed it last year I had to use nuts under the heads of the power street rack mount bolts to effective shorten them to clearance the bar. The ends of the ST bar are very thick - the studs on the factory S5 plastic front link ends are barely long enough for adequate thread engagement on the nut. One nut already fell off and I had to put new nuts on and use Loctite on the threads. I have the S5 link ends installed in the first (softer) setting now. I am not even sure that they will reach the second (stiffer) setting. I have the Mazdatrix adjustable link ends - but I have not install them as of yet.

Another issue is that the ST bar moves side to side. So to eliminate that issue I decided to buy some clamp-on split collars from McMaster-Carr to keep the bar centered. Unfortunately there was no room to install the split clamp-on collars on the outside of the mount bushings. I would have liked to locate the clamp-on collars there because the bar is still straight at that location and the collars would ride against the full side surface of the poly mount bushings. But there just isn't enough clearance between the bar and the uni-body frame rail on the outside of the mount bushing. I could not gain any more clearance by spacing the mount and bar away from the frame rail with some hardened washers because then the bar would again get too close to the power street rack.

I was not about to space the whole sub frame away from the uni-body to gain the required space. So my only choice was to mount the split clamp-on collars on the inside of the mount bushing. Not much fun due the the curvature of the bar at that location. There may also now be too much pressure on too small of an area on the side of the poly mount bushing as well. But there really was not much else I could do to keep this S4 ST bar from moving laterally in my S5.

I talked with a couple other folks about this, but they have the Racing Beat 1-1/8" front sway bar that has a slightly different shape and is designed for fitment on both the S4 & S5 models. It has a straight section on the inside of the mount bushing where you can install the clamp-on split collars. The RB front bar also come with some plastic collars to keep the bar from moving side to side, but some folks have removed them and used the same metal clamp-on collars that I used on the ST bar.

There maybe after all a good reason why ST had separate S4 & S5 front sway bar. But for me it sounds like I need to find a RB front sway bar. One more thing to add to the to-do list for Spring.

More photos with the clamp-on collars installed.

wow those ears are thick. I would deffinitly install the mazdatrix endlinks.

I have a 27mm (1-1/16") S4 whiteline bar on my S5 and my stock endlinks could be adjusted to all 3 of the bolt holes... and it doesn't hit anything that I'm aware of.

I finally got a round to removing the ST front S4 sway bar #50165 from my S5 GXL yesterday and installed the Racing Beat front sway bar #14103. The different in the installation, fitment and ride/handling was quite noticeable.

The RB bar fit the chassis perfectly with the ends of the bar being slightly tucked more inward so that the link ends are now vertical. The ears on the bar are also thinner now allowing the use of a washer and lock wash under the nut on the stock S5 link ends. The clearance to the radiator and steering rack in improved - noted that both of these front sway bars are 1-1/8" in diameter. I still used a single hardened washer for each bolt under the mounting brackets to limit the amount of crush on the poly mount bushings hoping to limit any binding. I had done the same with the ST S4 bar as well.

There is a noticeable improvement in ride quality - less impact harness and less bump steer. I would contribute that to the fact that there is now less pre-load on the bar due to the stock vertical position of the link ends and the fact that they are not so severally side loaded as with the ST S4 bar. There is a bit more initial front end roll (very progressive, linear and normal in feel) and the steering is not as hyper sensitive. Again most likely due to the correct more vertical position of the link ends and less pre-load. If I wanted to set the car up for track events, I would most likely install the Mazdatrix spherical link ends and adjust the pre-load on the bar. But for street use, the stock S5 link ends are perfect. The calmer less hyperactive feel to the front end is more welcome on the street - especially on less than perfect pavement.

One last note is that I am using the stock S5 front LCA. If you have back dated your S5 to S4 LCA so that you have replaceable ball joints, and use S4 link ends or spherical link ends like the Mazdatrix units, you may have a different/better experience with the ST S4 front sway bar on your S5.

I have an S4 with ST anti sway bars.
I've noticed that the front bar has moved about 1/4".
My racing beat end links are not sitting flush against the sway bar ears.

My biggest problem is that the sway bar with the end links are rubbing against my ksport coilovers (lower mount). I'll try capturing some pictures tomorrow, but from what I can see there is only about 1.5" of space between the sway bar and the lower mount, is this normal?