What's the real purpose of brake dust shields?
05-11-2011, 07:31 PM
#32
Chronic Tool Dropper
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Real hot. Real Glazed. Lots of squeeling. I like my pads the way I like my women...
05-11-2011, 07:34 PM
#33
i dont think its a dust shield either.i think its to shield the rotor from sudden large splashes of water which if it wasn't there would give you an ineffective brake for a split second while the pads clear the water off the surface face of the rotor.i wouldnt recommend binning these shields it could make you car dangerous to drive in wet conditions.
05-11-2011, 07:52 PM
#34
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Spent the day cleaning and painting my "almost new" dust sheilds.
So I did it for not mutch as fare as I can see.
I could have gone without them.
...But I like my car to be as close as possible as it was when it was new, so...
I guest Porsche did put them for something!
So I did it for not mutch as fare as I can see.
I could have gone without them.
...But I like my car to be as close as possible as it was when it was new, so...
I guest Porsche did put them for something!
05-11-2011, 08:50 PM
#35
Rennlist Member
I'm not totally convinced that they're there for water splash shielding, because pratically they don't seem to have much effect.
On the inside front of my GTS I can hardly see any of the inside of the wheel from underneath on the other side, so any water being splashed from there (the other wheel) can't even be aimed at the shield, let alone the rotor or caliper. Have a look under your own car and you'll see what I mean. The inside offset also restricts the chance of splash getting to the disc/caliper from any direction. At the rear the discs and calipers are so deeply buried in the offset I can't see how water could get there unless you were driving through it. I have difficulty getting water to those areas from underneath using a hose or when I pressure clean underneath.
On the outside, however, the discs get wet when it rains through the very open face of the wheel, so get much wetter in rainy weather than the inside. The outside also has minimal offset from the face and is much more likley to get splashes from elsewhere, and is easy to get to with a hose.
As for them being dust shields ... go have a look at the inside of your wheels and see how effective they are .... not.
Rocks/grit ... same applies ... more chance of entry from the outside face where you can see an open rotor and the caliper.
The other theory I've heard is that they direct the airflow to the centre of the rotor and improve the pumping effect of the rotor vanes, bit I've not seen compelling data that proves that either.
I too would like to know what the real purpose of them is.
On the inside front of my GTS I can hardly see any of the inside of the wheel from underneath on the other side, so any water being splashed from there (the other wheel) can't even be aimed at the shield, let alone the rotor or caliper. Have a look under your own car and you'll see what I mean. The inside offset also restricts the chance of splash getting to the disc/caliper from any direction. At the rear the discs and calipers are so deeply buried in the offset I can't see how water could get there unless you were driving through it. I have difficulty getting water to those areas from underneath using a hose or when I pressure clean underneath.
On the outside, however, the discs get wet when it rains through the very open face of the wheel, so get much wetter in rainy weather than the inside. The outside also has minimal offset from the face and is much more likley to get splashes from elsewhere, and is easy to get to with a hose.
As for them being dust shields ... go have a look at the inside of your wheels and see how effective they are .... not.
Rocks/grit ... same applies ... more chance of entry from the outside face where you can see an open rotor and the caliper.
The other theory I've heard is that they direct the airflow to the centre of the rotor and improve the pumping effect of the rotor vanes, bit I've not seen compelling data that proves that either.
I too would like to know what the real purpose of them is.
..... 
05-11-2011, 09:38 PM
#37
Rennlist Member
I'm not totally convinced that they're there for water splash shielding, because pratically they don't seem to have much effect.
On the inside front of my GTS I can hardly see any of the inside of the wheel from underneath on the other side, so any water being splashed from there (the other wheel) can't even be aimed at the shield, let alone the rotor or caliper. Have a look under your own car and you'll see what I mean. The inside offset also restricts the chance of splash getting to the disc/caliper from any direction. At the rear the discs and calipers are so deeply buried in the offset I can't see how water could get there unless you were driving through it. I have difficulty getting water to those areas from underneath using a hose or when I pressure clean underneath.
On the outside, however, the discs get wet when it rains through the very open face of the wheel, so get much wetter in rainy weather than the inside. The outside also has minimal offset from the face and is much more likley to get splashes from elsewhere, and is easy to get to with a hose.
As for them being dust shields ... go have a look at the inside of your wheels and see how effective they are .... not.
Rocks/grit ... same applies ... more chance of entry from the outside face where you can see an open rotor and the caliper.
The other theory I've heard is that they direct the airflow to the centre of the rotor and improve the pumping effect of the rotor vanes, bit I've not seen compelling data that proves that either.
I too would like to know what the real purpose of them is.
On the inside front of my GTS I can hardly see any of the inside of the wheel from underneath on the other side, so any water being splashed from there (the other wheel) can't even be aimed at the shield, let alone the rotor or caliper. Have a look under your own car and you'll see what I mean. The inside offset also restricts the chance of splash getting to the disc/caliper from any direction. At the rear the discs and calipers are so deeply buried in the offset I can't see how water could get there unless you were driving through it. I have difficulty getting water to those areas from underneath using a hose or when I pressure clean underneath.
On the outside, however, the discs get wet when it rains through the very open face of the wheel, so get much wetter in rainy weather than the inside. The outside also has minimal offset from the face and is much more likley to get splashes from elsewhere, and is easy to get to with a hose.
As for them being dust shields ... go have a look at the inside of your wheels and see how effective they are .... not.
Rocks/grit ... same applies ... more chance of entry from the outside face where you can see an open rotor and the caliper.
The other theory I've heard is that they direct the airflow to the centre of the rotor and improve the pumping effect of the rotor vanes, bit I've not seen compelling data that proves that either.
I too would like to know what the real purpose of them is.
A moving car..isnt gonna get wet in hidden areas like inside the wheel..like youre blowing a garden hose onto it.
A driving rain down the road, a light mist is about what the brakes are gonna see. No torrents of water..and a LOT of moving air, on warmer than ambient metal...spinning..wont catch non direct moisture worth much.
I do wonder...about certain brake materials and their ability to absorb moisture in cool/high humidity environments. Carbon loves it..the more of it, the more it'll suck up, to the point that full carbon brakes are a disaster as such cold.
05-11-2011, 09:44 PM
#38
Drifting
I must say that this topic has gone on longer then I thought it would.
As a long time automotive tech for General Motors with a engineering degree from your beloved LeTourneau Technical Institute, let me say that the manufacturing company dose not care about the brake dust.
[doesn't mean I know squat about a 928]
The shield is for more then one reason
It is to protect the rotor and pads from debre as well as to help with cooling the brakes.
http://books.google.ca/books?id=U4TB...page&q&f=false
BTW the brakes get very hot under normal applications
[quote]If you multiply horsepower by the proper conversion factor, you discover that one horsepower generates 42.4 BTUs of heat per minute. If stopping a 4,000 lb. vehicle from 60 mph in roughly 150 feet requires 600 horsepower of force, it is the equivalent of 25,440 BTUs of heat, which is enough heat to raise 15 gallons of water from zero degrees to boiling! No wonder the brakes get so hot.]
disc brake science
As a long time automotive tech for General Motors with a engineering degree from your beloved LeTourneau Technical Institute, let me say that the manufacturing company dose not care about the brake dust.
[doesn't mean I know squat about a 928]
The shield is for more then one reason
It is to protect the rotor and pads from debre as well as to help with cooling the brakes.
http://books.google.ca/books?id=U4TB...page&q&f=false
BTW the brakes get very hot under normal applications
[quote]If you multiply horsepower by the proper conversion factor, you discover that one horsepower generates 42.4 BTUs of heat per minute. If stopping a 4,000 lb. vehicle from 60 mph in roughly 150 feet requires 600 horsepower of force, it is the equivalent of 25,440 BTUs of heat, which is enough heat to raise 15 gallons of water from zero degrees to boiling! No wonder the brakes get so hot.]
disc brake science
05-12-2011, 01:08 AM
#39
Been selling Twinkies on Ebay,
have some extra cash right now.
Rennlist Member
have some extra cash right now.
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I had to remove my original dust shields when I went to the larger brakes.
With the stock brakes, the car would stop equally well wet or dry.
With the exposed rotors, the car stops much better in the dry, but much worse in the rain... aka wet rotor syndrome.
I changed to 17" rims at the same time, to clear the calipers.
With the stock brakes, the car would stop equally well wet or dry.
With the exposed rotors, the car stops much better in the dry, but much worse in the rain... aka wet rotor syndrome.
I changed to 17" rims at the same time, to clear the calipers.
05-12-2011, 03:05 AM
#40
Rennlist Member
Well guys, I have personel experience here. It seems we have the little storms here that are tropical in nature. My shark is my daily driver. I have been driving in hard rain and hit a long area where there were a couple of inches of rain on the road. If you don't think it will affect your breaks you are crazy. The best thing to do is just keep the car straight and hope you don't need them till you find hard serfice again. And yes I am talking about highway driving. God forbid you sould ever encounter such a thing on 2 wheels...
05-12-2011, 05:29 AM
#41
Rennlist Member
I must say that this topic has gone on longer then I thought it would.
As a long time automotive tech for General Motors with a engineering degree from your beloved LeTourneau Technical Institute, let me say that the manufacturing company dose not care about the brake dust.
[doesn't mean I know squat about a 928]
The shield is for more then one reason
It is to protect the rotor and pads from debre as well as to help with cooling the brakes.
http://books.google.ca/books?id=U4TB...page&q&f=false
As a long time automotive tech for General Motors with a engineering degree from your beloved LeTourneau Technical Institute, let me say that the manufacturing company dose not care about the brake dust.
[doesn't mean I know squat about a 928]
The shield is for more then one reason
It is to protect the rotor and pads from debre as well as to help with cooling the brakes.
http://books.google.ca/books?id=U4TB...page&q&f=false
I can't see any mention of shields in that document, although a few pages (such as 1244) aren't showing as available to read. Nevertheless it reads as a general shop procedure manual, and I'd like to see a bit more of an engineering/theoretical analysis with some data to back conclusions.
Like the OP, I'm interested to hear of the real purpose (and I'd like to understand the theory behind it), but I'd like to see some data and info that supports the design which includes a shield, so I can draw my own conclusions.
05-12-2011, 05:48 AM
#42
Rennlist Member
I had to remove my original dust shields when I went to the larger brakes.
With the stock brakes, the car would stop equally well wet or dry.
With the exposed rotors, the car stops much better in the dry, but much worse in the rain... aka wet rotor syndrome.
I changed to 17" rims at the same time, to clear the calipers.
With the stock brakes, the car would stop equally well wet or dry.
With the exposed rotors, the car stops much better in the dry, but much worse in the rain... aka wet rotor syndrome.
I changed to 17" rims at the same time, to clear the calipers.
05-12-2011, 06:57 AM
#43
Racer
Thread Starter
Wow! This thread has indeed grown bigger than expected.
FWIW, my daily driver Beemer had original brakes (always maintained by the previous owner @BMW dealers), but when driving the German Autobahn @160 km/h for about an hour through the rain, I had to hit the brakes. The first couple of hundred metres they were crap and didn't brake at all, untill all water was gone from the discs when finally the brakes bit hard and I came to a halt. All went well (just), but I didn't want to go through that again.
I changed the discs to EBC Ultimax BlackDash Slotted Rotors with Redstuff pads and have never had problems since... The shields are still there so nothing changed there. Braking performance has increased big time!
unscientific conclusion: the shields don't keep away massive amounts of water on the discs (maybe even forces water onto them?) and brake performance when wet comes more down to the material you're using rather than the design of the system.
All in all, I'll remove the dust shields like so many others have done. I'll just polish the wheels a little more often...
FWIW, my daily driver Beemer had original brakes (always maintained by the previous owner @BMW dealers), but when driving the German Autobahn @160 km/h for about an hour through the rain, I had to hit the brakes. The first couple of hundred metres they were crap and didn't brake at all, untill all water was gone from the discs when finally the brakes bit hard and I came to a halt. All went well (just), but I didn't want to go through that again.
I changed the discs to EBC Ultimax BlackDash Slotted Rotors with Redstuff pads and have never had problems since... The shields are still there so nothing changed there. Braking performance has increased big time!
unscientific conclusion: the shields don't keep away massive amounts of water on the discs (maybe even forces water onto them?) and brake performance when wet comes more down to the material you're using rather than the design of the system.
All in all, I'll remove the dust shields like so many others have done. I'll just polish the wheels a little more often...
05-12-2011, 07:07 AM
#44
Addict
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Dust and water aren't part of the equation. The sheilds may prevent gravel getting to the rotor/pad interface thus preventing paint chips to your nicely painted calipers.
05-12-2011, 08:36 AM
#45
Rennlist Member
S4+ (I can't speak for <S4) it is undeniably obvious that the whole point of the shield is to direct and funnel the air that comes through the hole in the spoiler then turned outwards by the rubber vane on the lower A arm to the central annulus on the inside of the rotor where the air the flows through the vanes in the centre of the rotor thus cooling it.
Dust and water aren't part of the equation. The sheilds may prevent gravel getting to the rotor/pad interface thus preventing paint chips to your nicely painted calipers.
Dust and water aren't part of the equation. The sheilds may prevent gravel getting to the rotor/pad interface thus preventing paint chips to your nicely painted calipers.
Maybe the shield stops that side of the rotor from being cooled more than the outside, which doesn't get the same airflow towards it, and ensures that cooling is predominantly from air pumped through the rotor vanes, and therefore you get inner and outer disc temps more even (less chance of warping and cracking).
I might give my GTS a good flogging and take some IR images to see what happens to the inside and outside of rotors thermally. When I get my 82 with S4 brakes (no shields) on the road again I'll do the same.