Does the RS4 have brake disc wiping?

[Eric F]

I found this PDF file for the launch of the RS4 in North America.

http://webpages.charter.net/parkhill/qw/2007_RS4.pdf

At the end in the technical specifications is says that the braking system uses Electronic Stabilization Program (ESP 8.0) featuring brake disc wiping.

From what I've been able to find, this system is supposed to apply the brakes briefly when the windshield wipers operate. Is it confirmed that our cars have this feature, and if so, is it possible to test if it is operating correctly?

I have a problem with the brakes not doing much of anything for approximately 1 to 2 seconds if I'm driving it in very heavy rain at highway speeds. You apply the brakes and literally nothing will happen for that length of time and then the brakes will function normally. I experienced this problem last fall with the stock brakes and this spring I purchased new brakes, this time going with Stoptech pads and rotors. Now that we're into the heavy rainy season I am experiencing the same problem again.

[ryanhmusic]

I'm not positive if it has it or not, but I can't imagine it being particularly effective if it only pulses the brakes once quickly when you put the windshield wipers on...the disks are just going to get wet again.

The simple answer is: leave a little more space and expect your brakes not to bite for a half a second -- however, if you really push down hard on them, they should bite quickly regardless of water or not, it'll just flash off.

Supposedly slotted rotors help keep the faces drier but I have no experience there and it might be a total wives tale...

[WinterRunner]

Eric I also get this, and it was most noticeable on Posi-centic pads being sometimes a full second before the bite, I now have Hawk ceramics and I still get the pause before the bite, but I'd say it is 1/2 a second at most. By any chance are you on ceramic pads??

[blubusdrvr]

I've never noticed (or heard of this). Now I have to take her out in the rain soon to check!

[koolade9]

I recall someone posting that we indeed have this feature.

The time delay you're experiencing is a combination of a very cold rotor warming up to temp, while simultaneously wiping the rotor of water. It's never going to be the same as a dry/warm rotor.

[4rings-rs4]

Marketing material says we have it.... never really felt it working (not even sure if it works all the time or is tied to rain sensors somehow). Braking in wet conditions has always been similar to dry - so I'm good believing we do!! :)

[OscarMeyer]

If memory serves me correct, the European RS4 has this feature enabled when the carbon ceramic brakes are installed, when initiating the wipers in the rain the car would automatically pulsate the brakes to keep the surface upto temp and clean of debris. I think I have the vagcom long coding somewhere, just need to dig it up.

Don't think this is enabled for steel rotor's though.

[CoreyRS]

I was under the impression that it was imperceptible to the driver because it essentially just drags the pad across the rotor with minimal pressure to both bring rotor surface to temp and wipe the surface. Im in the camp that it is more a marketing feature than anything else.

[ECS Tuning-Audi]

Slotted rotors definitely help with the delay as the slots act like the channels on a tire to help remove water. But ultimately you should practice proper driving habits and give more space between you and the vehicle in front of you during poor weather conditions.

Jason

[WinterRunner]

I recall someone posting that we indeed have this feature.

The time delay you're experiencing is a combination of a very cold rotor warming up to temp, while simultaneously wiping the rotor of water. It's never going to be the same as a dry/warm rotor.

I'm experiencing this after the car/rotor is warmed up though. I've never experienced this type of delay with any other car in my life. This was both with OEM rotors and the slotted JHMs

[Eric F]

Eric I also get this, and it was most noticeable on Posi-centic pads being sometimes a full second before the bite, I now have Hawk ceramics and I still get the pause before the bite, but I'd say it is 1/2 a second at most. By any chance are you on ceramic pads??

I am running the Stoptech Street Performance Pads. They refer to them as Para-aramid composites.

I'm experiencing this after the car/rotor is warmed up though. I've never experienced this type of delay with any other car in my life. This was both with OEM rotors and the slotted JHMs

I've also never felt this on any other car I've ever owned, including a Corvette Z06. Of course I expect braking performance to be reduced in the rain and drive accordingly. But this is the only car I've ever owned where literally nothing at all happens when I first step on the brake pedal in heavy rain.

[komseh]

Same thing happens to me, JHM rotors with Hawk HPS pads

[Reggie]

Eric I also get this, and it was most noticeable on Posi-centic pads being sometimes a full second before the bite, I now have Hawk ceramics and I still get the pause before the bite, but I'd say it is 1/2 a second at most. By any chance are you on ceramic pads??

I thought we had the wipe function on the RS. But I only noticed a delay when I had not been using the wipers. BTW I had posi on my car and the delay was not a second. More like milliseconds - and it was not that it was a delay before braking started - it was a delay before full brake pressure started working. but initially there was a bite on the brakes

[WinterRunner]

Okay so there's a few of us, it can't be a one-off anomaly at this point... IF there's no rain it's spot on, I'm lost on it.

[thomasskull666]

Same here, 1-2 seconds of severely diminished braking. I didn't experience this on my B7 S4, pretty annoying.

[CoreyRS]

Are you guys exaggerating at all? 1-2 seconds delay sounds extremely dangerous (i.e. ~90-200 feet @ 60mph).

Im am happy to report that I have never experienced this.

[badbluers4]

Are you guys exaggerating at all? 1-2 seconds delay sounds extremely dangerous (i.e. ~90-200 feet @ 60mph).

Im am happy to report that I have never experienced this.

Me either lol

[WinterRunner]

I would say like to say no, but not the case.

[forbiddenbeat]

Agreed, 1-2 seconds seems extremely dangerous. This doesn't happen with OEM pads and rotors - are you all still running OEM drilled rotors?

[blubusdrvr]

This doesn't happen with OEM pads and rotors

Well, this just makes me want to continue on with my stockers. Has anyone seen a pattern or commonality here? Certainly don't want to wait a few seconds for my binders to engage when I need/want them to.

[CoreyRS]

Im on JHM rotors/recommended pads...never felt it.

[thomasskull666]

It is variable how long it takes for full bite, the longer I go in the rain without using the brakes, the longer it takes to grab. I'm not sure if it's some sort of oxidation on the rotor surface or excess water or something else. I'm on stock rotors and pads.

[huntercross]

I just picked up an '07 RS4 about a month ago and it too has the same braking delay when it raining out. I have had multiple BMW's and an RS6 in the past, none of which had this issue. Of the nearly 20 cars I have had, only my 2004 Jetta GLI 1.8T had this same issue. It can be a bit startling at times, especially when you aren't expecting it.

[komseh]

I was thinking about this today and I'm hypothesizing that the extra brake cooling we have from the cooling ducts is the cause. The rain is already cooling the rotors down; adding the air increases the cooling efficiency quite a bit I would think. It probably cools the brakes to a point outside of the operating temp of the brake pads. What is the operating temp of a typical street brake pad?

Does anyone with aftermarket calipers have this issue? I don't think it'd be a design flaw in the brembo calipers, but you never know.


Maybe it just comes down to brake pad operating temperature.
I'm looking at the specs for my current street pads(Hawk HPS) and it says 100F is the minimum operating temp. I actually have a set of Carbotech 1521 pads, which they claim operates at ambient temp, on the way so I'll report back with results.

[Eric F]

Are you guys exaggerating at all? 1-2 seconds delay sounds extremely dangerous (i.e. ~90-200 feet @ 60mph).

Like others have already said, for me, it is unfortunately not an exaggeration. And I agree that it is extremely dangerous. I have to leave a HUGE gap between the car in front of me when I'm on the freeway in heavy rain. Like double the normal gap.

Agreed, 1-2 seconds seems extremely dangerous. This doesn't happen with OEM pads and rotors - are you all still running OEM drilled rotors?

I bought my car used last year and it still had the original pads and rotors. I did not have any problems with braking except in heavy rain. So I replaced the brakes because I assumed the performance in heavy rain was due to the brakes being too worn. I am now running Stoptech rotors and Stoptech street performance pads. The behavior in heavy rain has not changed at all. Not in the slightest. The brakes are absolutely fantastic except for when it rains heavily. If it's just light rain or damp roads the brakes perform normally. That is what lead me to believe that the brake wiping is not working on my car. Especially since apparently some people don't experience this problem at all. It would be nice to know if someone actually knows how to diagnose if it is working, or if that is what prevents the performance from deteriorating.

I was thinking about this today and I'm hypothesizing that the extra brake cooling we have from the cooling ducts is the cause. The rain is already cooling the rotors down; adding the air increases the cooling efficiency quite a bit I would think. It probably cools the brakes to a point outside of the operating temp of the brake pads. What is the operating temp of a typical street brake pad?

Does anyone with aftermarket calipers have this issue? I don't think it'd be a design flaw in the brembo calipers, but you never know.

I don't think it's related to temperature. I can drive 30+ miles on the freeway at 60+ mph without touching the brakes at all. I can do that at below 30°F and the brakes work perfectly when I exit the freeway. I can do that with damp roads or light rain and the brakes work perfectly when I get off the freeway. But if it's heavy rain, the brakes will do nothing when I first step on them when I get off the freeway. My Z06 also had brake cooling ducts and never experienced this problem.

The only thing I could find when trying to research this problem on the internet is that some people have complained about the design of the splash shield on the RS4. I don't know if that could be it or not, and if it is, why doesn't everyone have the problem?

[AussieDan]

I have experienced what you're talking about, but only once that I can recall. Stoptech street pads on stock rotors.

[AvusPdx]

I experienced this in heavy rain as well. I can also hear a vibrating squeak type noise when this occurs. 1 - 2 second delay. I assumed it was water collecting between the components.

[Fritz_S4]

Quick question for everyone that has this problem... what wheels are you running when this happens? OEM or aftermarket?

I ask this because my B6 S4 does this with the RS4 reps I have on but not when I switch over to my winter set.

I think it has to do with the wheel design. The RS4 OEM wheels have flat spokes (perpendicular to rotor face) which send a fair amount of water inwards onto the rotor face. My winter set (S4 rotors, not peelers) have angled spokes that look like they would tend to push water outwards in heavy rain. Anyone ever consider this in their analysis

[komseh]

Fritz, thats a good point. I was also thinking maybe the brake ducts are getting extra water on the brakes.

[WinterRunner]

Interesting insight, I am on stockers.

[thomasskull666]

Same, also on stock wheels.

[forbiddenbeat]

It is variable how long it takes for full bite, the longer I go in the rain without using the brakes, the longer it takes to grab. I'm not sure if it's some sort of oxidation on the rotor surface or excess water or something else. I'm on stock rotors and pads.

Hmm, I suppose now that I think about it, I haven't driven the car in truly heavy rain (I'm assuming you're talking about crazy heavy thunderstorm rain), since we so rarely get that in California. I'll have to keep an eye out for this next time it rains.

It looks like this kind of issue happens to a lot of other cars (e.g. http://forum.e46fanatics.com/showthread.php?t=68805).

[WinterRunner]

The weird thing is I don't get this in snow, cold weather etc, only heavy rain, and only on the highway... That thread did prove to me insightful though FB, thanks.

[thomasskull666]

Hmm, I suppose now that I think about it, I haven't driven the car in truly heavy rain (I'm assuming you're talking about crazy heavy thunderstorm rain), since we so rarely get that in California. I'll have to keep an eye out for this next time it rains.

It looks like this kind of issue happens to a lot of other cars (e.g. http://forum.e46fanatics.com/showthread.php?t=68805).

Yep anything other than moderately heavy rain doesn't have an effect. In drizzle or light rain conditions the brakes work just fine.

The weird thing is I don't get this in snow, cold weather etc, only heavy rain, and only on the highway... That thread did prove to me insightful though FB, thanks.

I haven't driven this car in snow yet, but I live in St Louis so I'm sure we'll get some at some point. Will be interested to see if it happens for me then or not. It has gotten down to around 20F here a few weeks back, no issue.

[AvusPdx]

stock wheels but with spacers. Maybe the spacers have to do with anything?

[thomasskull666]

Jeez we're going to need to compile a spreadsheet here, spacers here also. 10mm all around.

[huntercross]

I too have stock wheels with spacers. I think the wheel design theory is a good one, but that still doesn't excuse why the "brake wiping" feature does not appear to work

[WinterRunner]

I am currently NOT running spacers, but I've seen the same with and without 10mm MTM's.