DaytonaB9

I wanted to see who has upgraded sway bars on their B9 S4 and how much of an improvement was noticed. I am debating whether to do just a rear sway bar upgrade or both the front and rear. I definitely want less body roll than stock but without getting into the territory of too stiff where I begin getting rattles and compromising the comfort too much. I also plan to get lowering springs or coilovers. I see the options for sway bars are 034 Motorsports and EMD Auto. Any others?

DaytonaB9

I also noticed the sway bars available are compared to the OEM A4 sway bar size/stiffness. I assume the OEM S4 sway bar is stiffer but does anyone know the OEM S4 sway bar specs?

mplsbrian

If your only desire w/r/t a sway bar is to reduce body roll, and you are already planning to get coilovers or springs, definitely do that (coils or springs) first, break the new suspension in with a thousand miles or a couple spirited track days, and reevaluate whether you need a bar upgrade from there.

As you probably know, a sway bar's purpose is to mechanically mate the left and right side independent suspensions of a car together, and limiting body roll is essentially just a side effect of that. It offloads some of the work your strut assembly would normally do onto the torsional resistance of the bar itself, and the thickness of that bar (all other things e.g. bar shape/mounting positions etc being equal) determines how rigid that mating is. A far more advanced and effective way to reduce body roll is to increase the spring rate/damping performance of the 4 independent corners themselves (and then you can put a sway bar that is better tuned to that specific suspension if you still feel there are gaps).

The B9 platform has an extremely advanced independent front/rear suspension system and, in my opinion, putting a monster sway bar on it to effectively weld the two sides together so they are far less independent than originally designed is a step that greatly cheapens the car's maximum handling capacity and overall comfort in situations where the road isn't level or perfect, aka most major city street driving scenarios.

Bobby Kinstle

So far I haven't really seen any problems with body roll on mine yet. Seems a lot better than my 2013 S4

dbuxton13

As long as the car comes properly spec'd with the sports suspension, there's no need for sway bars. The car stays planted in the corners with very little roll. You can see this in action on all 72 bends of the Nurburgring video I posted in a different thread. For a car that is designed more 'daily driver' than 'track car', it sure holds its own. I have been very pleased with this car... even stock.

adg44

A bigger sway bar doesn't mean "better handling". These have to work together in pairs to maintain the correct driving dynamics, and you can be assured this was done during technical development of the suspension/chassis.

DaytonaB9

I guess no one has experience with aftermarket sway bars on the B9 S4. I am waiting for KW to release their coilovers. My F80 M3 on KW with sways bars was much more responsive and flat after the modifications and even comparing the stock F80 to B9 S4. I will just move forward with the modifications I planned on. So far I have the ECS Tuning Front Tower Bar and it did improve the turn in and steering response slightly. Manufacturers design vehicles with more than performance in mind. Its designed for comfort, quietness, longevity, cost, value, etc. So you can't tell me the B9 S4 is fully optimized for performance with the OEM suspension parts.

m332is

Mr. Three

Both O34 and Eurocode have a full set (front and rear) of bars for the B9 chassis. 034 cautions you that installing the full set will negatively affect ride quality which to a certain extent, I would expect on any sports car. However, many in the Audi community don't take the step to the full set of bars because Audis have traditionally been nose heavy and stiffening up the front would supposedly cause additional understeer. Hence reason many in the B8 and now B9 community have done just the rear bar upgrade...of which 034 and EMD both offer an upgraded rear. I have chosen to do just springs and upgraded rear bar to keep the ride semi compliant and to have a bit more aggressive turn in. I did the same on my 2015 S5 (rear bar and springs) and the difference was noticeable but perhaps not night and day different. An F80 would certainly be a slightly different animal as it's rear drive and from what I understand a bit tail happy. Good luck!

mplsbrian

Mr. Three hit the nail on the head. Adding on to what he said, generally you install a front strut bar if you want to make the car plow more/add understeer, and you upgrade the rear bar if you want to increase oversteer. Strut tower bracing and thick rear sway bars have "side effects" such as increasing steering precision by way of welding the two sides of the car together, but the main effect they have on handling is adding understeer (front bar) or oversteer (rear bar) when upgrading them independently.

Now, obviously if you upgrade both the front and rear bar together it is possible to firm up the chassis without compromising (too much) the front/rear bias of the factory chassis dynamics, but the result can be (as 034 advised) a rather unforgiving ride on the street...so much so that you might find a wheel off the ground from the force of the rear bar alone when angling out of driveways or going over bumps. You also, by eliminating body roll, begin to ask a lot of the tires and shocks: steering will transfer force to them immediately, and this can actually decrease grip in many situations because you are "skidding" turning forces into the tire quite immediately rather than allowing a working tire progressively as a car would do when allowed to have some slight sway, which lets the tire take on more total load.

Like everything else in automotive design, suspension tuning is all about choices and compromises: Do I want to completely eliminate body roll and offload work to my tires, or do I want more effective lateral grip by allowing some sway so that my tires and shocks work together. Do I want daily driveable comfort with a little sway, or immediate steering response/precision with none. Do I want understeer, neutral handling, or oversteer.

But, as long as we are discussing this, I would be very curious to know what the B9 RS4 uses for front/rear sway bars vs. the S4. I know once upon a time the Honda Accord I4 would use a 13mm rear sway bar, the V6 got 15mm, and the Acura TL (which shared a chassis with the Accord) would get a 17mm bar. All were direct-fitment replacements for eachother and a common upgrade/swap in that community back in 2008-2012.

Maybe somebody can do some research on that? I do know the RS4 gets beefier shocks--Audi distinguishes this in their marketing by saying the RS4/RS5 get the "RS suspension" as compared to the S4's "S suspension," and each car offers both a fixed and an adaptive option. It'd be interesting to know what Audi's vision is for this chassis's supposed "top end" and how that compares to the current S4 aftermarket bar offerings.