Impressions: Swapping S5 rear sway bar to S4 with adaptive dampers and sport diff

[xtremepsionic]

Why install a thicker rear sway bar?

After searching fruitlessly on the forums looking for someone who's installed ONLY a thicker rear sway bar on their S4 with full ADS and sport diff, I decided to try it myself. I'm used to the superb balance of the E46 M3, and the stock S4 with full ADS understeers a lot more than I like, especially on turn in. Got myself a S5 rear sway bar (21.7mm, same size as normal S4) and swapped out the stock ADS S4 bar (16mm). The reason why I decided not to get a full sway bar package with thicker front and rear bars is that I live in northern Canada and the roads are very rutted/potholed. Most of my commute is unfortunately on perfectly straight highways. So I wanted to keep the superb ride quality and independent suspension intact. Even though there is some bodyroll and the S4 does take a split second to settle into corners, I'm happy with the compromise for the style of driving I do. I didn't want to install one of the aftermarket 24mm rear bar by itself, as it is another 100% stiffer than the S5 bar, and might make the car too tail happy since I'm keeping on the stock front bar.

Impressions:

Install was not fun, but there are other DIYs out there so I won't say more. The car now understeers very little. I can chuck the car into a corner without first transferring weight to the front via braking or lifting, and the car won't plow like it used to. There's definitely some rear rotation mid corner when I lift off the throttle a bit, but it's not so much that you'll need to countersteer. The car feels more neutral and more willing to follow steering input. It's very close to being perfect now and feels less front heavy. Fit is OEM and there are no rattles or squeaks.

Under power with sport diff set to dynamic, the car feels almost RWD. There's definitely some slight amounts of oversteer and once power is applied, I could actually back off on the steering angle a bit, good stuff!

Overall I think this is a really nice and cheap mod for someone with full ADS to dial out understeer without making the car ride any harsher.

[emnahum]

Thanks for the informative post. I also have ADS with the sport diff and have been thinking about sway bar options. I will probably go Eurocode but this is an interesting option.

[cspcrx]

Well done and great find that its a direct swap. Probably pick one up used for a lot less than an aftermarket rear bar.

[LBosh]

Thank you for sharing this with us!
I'm actually contemplating doing the same thing on my ADS S5.

There is one more OEM sway bar 19.6 mm thick; my be it's a better fit? What do you think? I don't want to make my car too tail-happy.

[onlyaudis]

what car came with the 19.6mm bar --is that from the A4 sports suspension? I have upsized the rear bars on just about every Audi I have ever owned with a slightly larger factory bar from another model, and have always been happy with the results

[xtremepsionic]

Thank you for sharing this with us!
I'm actually contemplating doing the same thing on my ADS S5.

There is one more OEM sway bar 19.6 mm thick; my be it's a better fit? What do you think? I don't want to make my car too tail-happy.

Nah, if anything I'd try to get the RS5 rear bar instead which is 22.5mm vs the S4/S5 bar which is 21.7mm. This 21.7mm bar I got is just on the understeer side of neutral. I tried some aggressive left/right wiggles at about 40mph and there's not enough rear bar to make the rear end come out.

[drob23]

Yea the stock rear ads bar is very small. I think this allows them to give the "comfort" mode a lot more of a floaty feel with less aggressive damping. I wouldn't be surprised if a non ads s4 rear bar was a similar upgrade to what you found with the s5 rear bar.

[xtremepsionic]

Yea the stock rear ads bar is very small. I think this allows them to give the "comfort" mode a lot more of a floaty feel with less aggressive damping. I wouldn't be surprised if a non ads s4 rear bar was a similar upgrade to what you found with the s5 rear bar.

Non ADS S4 bar is exactly the same as the S5 rear bar I put on, so you're absolutely right about that.

One interesting note however, the S5 bar seem to weight about the same as the ADS bar. I swear to god it feels like the S5 bar is hollow. I didn't weight them to compare though, just a note.

[onlyaudis]

you have a part number on either of the 21.6mm bars? besides the classifieds and ebay, where would be a place to look for one? wonder what they cost new, as the 24mm B6 RS4 bar was only $100 or so new.

[drob23]

Non ADS S4 bar is exactly the same as the S5 rear bar I put on, so you're absolutely right about that.

One interesting note however, the S5 bar seem to weight about the same as the ADS bar. I swear to god it feels like the S5 bar is hollow. I didn't weight them to compare though, just a note.

I think they are all going to be hollow. Helps reduce weight. The spring rate of the bar will be dependent on the outer diameter, the inner diameter, and the material properties.

And for an aftermarket adjustable bar, spring rate will be a function of where the end links bolt on. The closer the hole is to the rotation axis of the bar, the higher the spring rate = stiffer bar.

[ExhaustNote]

If anyone is interested, I have a Stasis rear sway sitting in my garage that I used on my old B8 S5. It's super thick at 27mm and is in great condition.

[xtremepsionic]

you have a part number on either of the 21.6mm bars? besides the classifieds and ebay, where would be a place to look for one? wonder what they cost new, as the 24mm B6 RS4 bar was only $100 or so new.

https://www.ecstuning.com/Audi-B8_S4...Bar/ES1894016/

https://www.ecstuning.com/Audi-B8_RS...Bar/ES2556779/


There's the rs5 and s4 bars.

[the4siswickid]

https://www.ecstuning.com/Audi-B8_S4...Bar/ES1894016/

https://www.ecstuning.com/Audi-B8_RS...Bar/ES2556779/


There's the rs5 and s4 bars.

Will the RS5 bar also fit a 2015 MY?


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[xtremepsionic]

Will the RS5 bar also fit a 2015 MY?


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Don't see why not, the chassis remains the same. Pretty sure all the after market companies offer sway bar sets which fits s4/a4/s5/rs5.

[cspcrx]

So i have ads lite, everything but the adjustable dampening. That means i have the larger bar already?

[14S4GWM]

^Don't think so

[xtremepsionic]

So i have ads lite, everything but the adjustable dampening. That means i have the larger bar already?

Yes, you already have the 21.7mm rear bar. Only the full ads models with adjustable dampers come with 16mm rear bar.

The reason isn't clear, but most probably the dampers stiffen up the rear to compensate in hard cornering, and the softer bar allows for better ride quality in other situations.

[14S4GWM]

I learned something new. Thanks. Seems odd though.

[lowjonathan]

Why install a thicker rear sway bar?

After searching fruitlessly on the forums looking for someone who's installed ONLY a thicker rear sway bar on their S4 with full ADS and sport diff, I decided to try it myself. I'm used to the superb balance of the E46 M3, and the stock S4 with full ADS understeers a lot more than I like, especially on turn in. Got myself a S5 rear sway bar (21.7mm, same size as normal S4) and swapped out the stock ADS S4 bar (16mm). The reason why I decided not to get a full sway bar package with thicker front and rear bars is that I live in northern Canada and the roads are very rutted/potholed. Most of my commute is unfortunately on perfectly straight highways. So I wanted to keep the superb ride quality and independent suspension intact. Even though there is some bodyroll and the S4 does take a split second to settle into corners, I'm happy with the compromise for the style of driving I do. I didn't want to install one of the aftermarket 24mm rear bar by itself, as it is another 100% stiffer than the S5 bar, and might make the car too tail happy since I'm keeping on the stock front bar.

Impressions:

Install was not fun, but there are other DIYs out there so I won't say more. The car now understeers very little. I can chuck the car into a corner without first transferring weight to the front via braking or lifting, and the car won't plow like it used to. There's definitely some rear rotation mid corner when I lift off the throttle a bit, but it's not so much that you'll need to countersteer. The car feels more neutral and more willing to follow steering input. It's very close to being perfect now and feels less front heavy. Fit is OEM and there are no rattles or squeaks.

Under power with sport diff set to dynamic, the car feels almost RWD. There's definitely some slight amounts of oversteer and once power is applied, I could actually back off on the steering angle a bit, good stuff!

Overall I think this is a really nice and cheap mod for someone with full ADS to dial out understeer without making the car ride any harsher.

hi there

does that S5 rear bar U bracket and bushing same as the old one 16mm bar? do they share the same part number for the metal bracket?

But the bushing is different due to the internal diameter? 16mm versus 21.7mm??

thanks

[xtremepsionic]

hi there

does that S5 rear bar U bracket and bushing same as the old one 16mm bar? do they share the same part number for the metal bracket?

But the bushing is different due to the internal diameter? 16mm versus 21.7mm??

thanks

Mine came with the bracket and bushing on the bar. The bracket looks about the same but there's no way you could use the same bushing from the 16mm bar on the 21.7mm one.

No idea where to get replacement bushings for the 21.7mm bar either. I wanted to put new bushings on but couldn't find it online. I found front bushings but not the rear.

[lowjonathan]

thanks man

[onlyaudis]

Install was not fun, but there are other DIYs out there so I won't say more

we talking having to drop the subframe not fun, or what? got a link to install DIY?

[drob23]

we talking having to drop the subframe not fun, or what? got a link to install DIY?

Eurocode has a DIY pdf if you look for their sway bars. You have to partially drop the exhaust.

[onlyaudis]

had mine up on a lift today, and saw where the rear bar was mounted. similar to other audis I have had. What's your take at this point on the ride quality degradation from the larger bar? In the comfort mode, is there a noticeable stiffer feel or not? I am pretty sure I would enjoy this inexpensive upgrade, and have a line on a bar already. not too hard to swap it back if I don't like the affect either.

[Lamprey]

had mine up on a lift today, and saw where the rear bar was mounted. similar to other audis I have had. What's your take at this point on the ride quality degradation from the larger bar? In the comfort mode, is there a noticeable stiffer feel or not? I am pretty sure I would enjoy this inexpensive upgrade, and have a line on a bar already. not too hard to swap it back if I don't like the affect either.

I can't speak for a just a rear replacement, but I did the Eurocode front and rear sways with endlinks and everything is certainly "tighter." It doesn't seem like it is really any more stiff/harsh in a bad way, rather, it's just much more tight and responsive. Additionally, the body roll is significantly reduced. Just an awesome upgrade all the way around!

For clarity, I have a 2013 with full ADS.

[xtremepsionic]

had mine up on a lift today, and saw where the rear bar was mounted. similar to other audis I have had. What's your take at this point on the ride quality degradation from the larger bar? In the comfort mode, is there a noticeable stiffer feel or not? I am pretty sure I would enjoy this inexpensive upgrade, and have a line on a bar already. not too hard to swap it back if I don't like the affect either.

The ride quality difference on a full ads with the 21.7mm bar is hardly any different. I'm pretty sensitive to changes like that and I love tweaking the damper settings based on the road surface. It's honestly pretty much the same.

I've installed thicker front and rear sway bars before on a wrx, the ride usually feels firmer when you increase roll stiffness front and rear by 1-2x together. When you hit a one sided bump it translates into more of a firmer jolt on both sides of the suspension and tosses your head a bit more. You are effectively increasing the spring rate in that particular scenario.

But since most of the weight and all of the steering feel is dictated by the front suspension on the s4, the ride quality difference with just a approximately 1x increase in the rear sway bar doesn't really register.

After driving a couple more days with this tweak I must say I'm very pleased. The body roll is still there, and turn in doesn't feel too much shaper, but the handing balance is right on the realm of neutral. Once the suspension is loaded up in the corner you could totally adjust how much rotation you want from the car with throttle input. The car just feels much less front heavy, agile and tossable.

If you can live with a slightly harsher ride, I can totally understand installing a full set of sway bars front and rear. That will obviously make the car feel much shaper. But for me this compromise works great, there are simply too many rutted pavement where I live, and there are unfortunately only 5% corners on my commute.

[onlyaudis]

so I just measured my rear bar, and its 22.5mm. PO must have had the RS4 bar already installed on the car. No wonder it seemed to turn in pretty flat already.

[the4siswickid]

Does anyone know where to pick up the RS4 sways and end links - new? ECS cannot help. I know we can get the RS5 rears there, but they cannot get the RS4 fronts... the RS5 fronts obviously won't fit the S4's.... I want to maintain relative stock to not trigger dealer shit storms.

[xtremepsionic]

Does anyone know where to pick up the RS4 sways and end links - new? ECS cannot help. I know we can get the RS5 rears there, but they cannot get the RS4 fronts... the RS5 fronts obviously won't fit the S4's.... I want to maintain relative stock to not trigger dealer shit storms.

http://www.audizine.com/forum/showth...-2010-A4-Avant

This person had it fit on his A4. Don't see why it wouldn't work on the S4?

[the4siswickid]

http://www.audizine.com/forum/showth...-2010-A4-Avant

This person had it fit on his A4. Don't see why it wouldn't work on the S4?

Excellent. Thx and just ordered!!!!!!


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[whts4]

we talking having to drop the subframe not fun, or what? got a link to install DIY?

Installing the rear bar does not require dropping the subframe. Several installs on here and youtube shows how to do it wo/subframe drop.

[whts4]

I've had a B8 and a B8.5 both without the ADS suspension option. The only significant difference btwn them was B8.5 has the sport diff. The stock bar size on the B8 was 21.7mm, while the B8.5 is 19.6.

Let's talk stiffness changes vs dia. As a general rule once you near the baseline of a 20mm dia bar the stiffness changes about 20% for each mm change in dia. So a change from 19.6 to a 21.7mm dia bar would be approximately 40% stiffer. A shift from 21.7 to a 22.5 would be approx another 20% or 60% from the 19.6.

Going from a 16mm to either a 19.6 or 21.7 would be a nice and inexpensive tweak.