AudiForums.com - The 411 on using S4 suspension on your A4

I had posted this on AudiFreaks a couple years ago and figured I'd import it here for the newer guys that might be considering this for their cars.

OK, it seems that in the last year or so on the boards there have been more and more people wanting to upgrade their A4's suspension using OEM S4 components. I've gone through a couple rounds of this and thought I'd throw my impressions out there for anyone in the future who is considering it. A caveat for this post - I'm only talking about B5 generation cars (most of us have them anyhow, but in case this comes up in Search for a B6/7 owner, don't take it as gospel).

First off, the benefits. One, it's definitely inexpensive since S4 guys upgrade to aftermarket gear as often as A4 guys do, so there's no real shortage of S4 suspension parts out there. Two, it's OEM quality, so even if you source a setup that's got considerable mileage, chances are it's still gonna be good. Three, install is plug and play, zero modification needed - S4 parts bolt directly into our A4s. Four, it definitely improves the car's dynamics.

Downsides? If you're looking for a decrease in ride height, look elsewhere. You'll come down some, but not much. We're talking an inch or so (vs non-sport suspension heights). Upside to that is you can always throw aftermarket drop springs on the S4 struts - they're beefy and can probably take the preloading better than your non-sport OEM A4 struts can. Also, if you have a 1.8T and use the S4 springs, you'll see an increase in ride height - your front end is quite a bit lighter than the S4's front end in particular, so using S4 springs on the front of your 1.8T is going to end up with a lift. Use the struts, but find 1.8T-specific springs, whether they're OEM S-line or aftermarket.

OK, my car is a 99 A4 2.8L manual quattro, 30v AHA, on 18" wheels, with 225-40ZR18 tires. I started with non-sport struts and springs, OEM A4 sway bars. First round was a direct swap of S4 springs onto my A4 struts. What I found from it was:

- a drop in ride height of about a finger-width
- a much firmer ride (not harsh or unpleasant, but more of exactly how I envision a near-luxury/sport German car should ride)
- some jarring on impacts with sharp expansion joints
- no apparent wear-out of my admittedly high mileage OEM A4 struts
- much better turn-in and roll resistance than with A4 springs
- better reflexes in quick lane change maneuvers

This past weekend, a few of the guys came over and we removed the A4 strut/S4 spring combo at each corner, and replaced it with full S4 strut/spring combos at each corner, plus removed my A4 rear swaybar and replaced it with an S4 rear bar. Looking at the S4 bar, it was hard to imagine that thing as an upgrade, but on comparing the A4 bar with it, it seems to be a 40-50% larger diameter, so judging on looks alone, it should make a difference.

Once again, install of all the parts (struts, springs, sway bar) are direct plug and play with no black magic, special techniques, or modification necessary. Install went smoothly, with the exception of getting the A4 end links unbolted from the A4 swaybar. The bar I got did not include the endlinks, which made it somewhat of a pain - the upper connection from endlink to hub is a bolt-nut combo, but the lower one is a ball-joint style threaded rod with a nut. The end of the threaded section has a 5mm Allen socket cast into it, with the idea that you can put an Allen wrench in there to hold the shaft steady so you can loosen the nut with a 17mm wrench. Dream on - we tore out the Allen shaping in about 30 seconds on my first link, and didn't bother on the second. What worked was soaking it with penetrating oil for awhile, then hitting it with the impact gun to loosen it somewhat. Finally we put big channelock pliers on the larger section behind the end link next to the boot (when you look, you will see what I mean), clamped it down tightly, and gunned the nut off. It would also help to use a stiff wire brush on the exposed threaded section before loosening the nut, to get grit and rust off the rod.

With everything installed, my impressions compared to the A4 strut/S4 spring combo are:

- nicer ride quality than before - bumps that were somewhat jarring with the A/S combo are now absorbed more smoothly than before (likely due to the fact that the valving of S4 shocks will be tuned to the spring rate of the S4 springs, whereas with A4 shocks, the complementary tuning isn't there compared to the S4 springs)
- yet another increase in reflex response when jerking the wheel in a quick maneuver - it really goes where you want now
- remarkable increase in cornering flatness - the attitude of the car in a hard-driven bend is much flatter than before (the S4 bar's billing as an upgrade is definitely upheld according to the ass-g-meter). Our cars have a 50/50 torque distribution and are nose-heavy, so stiffening the rear helps to rotate the car more willingly through a turn
- the car is seriously stiff now - dropping my 245-lb self onto the seat compresses the suspension maybe an inch or so, no more than that (Hiwords was there, and if he had sat in the car I doubt it would've moved)
- additional lowering, if any, is miniscule IMO - my parts sat uncompressed in the prior owner's basement for a few years, so if they're going to settle further, it'll be over the next week or so, but I'm not holding my breath for any real drop. Again, if you want low, shop the aftermarket

Overall, if you're not looking to really drop the car (maybe you don't like lowered cars, don't want to deal with the abnormal tire wear from negative camber, want to improve the handling without putting your oil pan in harm's way, or just came across a good used set and wondered if they were worth installing), the S4 setup is a great mod. For the 1.8T drivers, get the rear bar and struts, and fit aftermarket (or OEM S-line) springs appropriate for your car, and you'll love the difference. Until I go low later on this year, I'm very happy with this combination - it makes a solid car feel even moreso, corners WAY better (that rear bar is a great budget mod), transitions better, and feels more buttoned-down than the A4 setup could hope to feel. The parts are out there at very reasonable prices - go get 'em.