Cross drilled, Solid or grooved????

[Bushy]

Well I have read a few other posts kinda asking the same thing so I thought I would put my thoughts down for other people to share and comment on. Please note this is purely my understanding so dont assume it is factual!

Solid - OE
Well my opinion is that they have been designed for slowing the car down from whatever speed, not always quickly but wok well enough for motorway/autobahn crusing, the odd emergency stop and general round toown driving.

I assume Audi had some way of working out the braking force required to comply with the EU highway code [img]images/graemlins/spineyes.gif[/img]

The trouble with this is that a by product of friction/braking is heat so under normal braking the heat is dissapated by the air travelling around the disc as you continue on your journey. However under heavier more consistant braking the heat builds up and doesnt dissapate. This is where problems occur. The pad can begin to fade and then with continued use will glaze and make braking less efficient once the pad has cooled down.

This can be remedied by chaging the type of pad, as different friction materials react differently under heat. I think this will deserve a further thread

see here

Cross drilled or cast?

So in an attempt to get rid of the heat that causes so much problem manufacturers have tried various things. Cross drilling the disc is a good idea in theory as it increases the surface area and possibly gives air flow from the vented centre section of the discs to the pads surface

However cross drilling can cause a different problem as the hole can have a burr on it or a slight splinter where it has been drilled, this heats at a different temperature to the rest of the surface then starts to crack, so thats no good. Movit/Brembo went a step further and designed superior centre vanes with cast holes, so less chance of cracking by improved air flow as well. However they still can because if you use a harder compound pad the edge of the hole becomes worn and the same thing happens as a cross drilled disc - IMHO So my theory is to use a softer pad and change regularly as the pads are cheaper than discs

Grooved

I originally thought this was not such a good idea as OK you have improved surface area and therefore aided cooling but where the centre of the pad meets the disc you will have a heat build up like a normal pad

However after my recent day out at Donnington and the glazing of the pads on the way home and the next few days I think the grooves would remove the surface of the pad, ok more wear but it could stop the glazing

May be a combination of both is the best option

Please post your comments as this is an interesting thread for people about to upgrade

[jeffw]

My thoughts on the subject.....for what it's worth

X-Drilled

This method will reduce the temperature of the disc but can suffer from glazing.

Drilled Holes are going to crack because of the stresses introduced in the production method. You may even end up with the disk disintegrating (or exploding)....not a good idea.

Cast holes should be better and (I think) this is the most common method. However as you wear the disc (especially if you hot spot them) more wear will occur on certain hole edges and you could get cracking.

Grooved discs will de-glaze the pads very well as it's the leading edge of the pad that does most of the braking effort. They will also heat up in a uniform manner (like solid or plain discs) although they will run hotter than the equivalent drilled disc. I believe that grooved discs will last longer than X-Drilled and are less likely to fail due to cracking.

X-Drilled (cast) & Grooved discs are probable the ultimate as far as stopping power is concerned but will probable wear quicker than grooved.

Interestingly the big budget teams in motorsport tend to use X-Drilled & Grooved (where carbon brakes are not allowed) where as the privateer teams use Grooved Only.

[Bushy]

[quote I believe that grooved discs will last longer than X-Drilled and are less likely to fail due to cracking.
[/quote]

My only comment to this would be they would then be more likely to warp due to heat retention.

Do you think?

[jeffw]

If the rotor is mounted on a bell then I don't think so. The whole disc is going to expand and contract at the same rate.

The other important aspect to all of this is how you run your discs and or Pads in.....

[tanoga]

Well after my last track day on standard brakes I am looking into the upgrade options.
It is a mine field.
I want brakes that will work on the road and track.
I want them to last as well.
I firmly believe the biggest issue is the removal of heat,
and it is based on that which leads me to look into the following set up for the front only to start with:-

6 Pot Water cooled caliper (painted yellow)
Grooved disc.
Pads to be determined.

At the moment no one makes the above for the RS4 so I am going to have to make it myself if it can be done.

Karl

[Bushy]

Blimey Karl, i am going to go back to standard until you get this sorted

Nice one mate.

What about modifying someone elses design instead of starting from scratch?

[jeffw]

Well...

My aftermarket brakes have now done 3 track days (500 on track miles) and about 8000 miles on the road. The pads are OK and the discs are fine as well. They have never faded on track. The pads are Ferodo DS2500, Discs are HiSpec Grooved 335 x 32 (vented with vanes) and HiSpec Monster 4-Pot calipers. One of the issues with the S4 (and the RS4 to a lesser extent) is the venting of the air that has past through the intercoolers into the wheel arch.

I think that water cooling is OTT for what is basically a road car. You maybe better looking at 6-pots with grooved disc and some brake ducts.

[kcsun]

I think Hammerite does a nice shade of yellow Karl [img]images/graemlins/spineyes.gif[/img]

I am going to continue with the free replacements after each track day from Audi route - till the warranty expires anyway [img]images/graemlins/colflash.gif[/img]

kc [img]images/graemlins/s4anogaro.gif[/img]

[tanoga]

Jeff,
Water cooled OTT is what everybody is telling me, but I cannot find anyone with an RS4, apart from Steve(rs4steve), who is 100% happy with there set up.
Ask Bushy and JR how much time money and trouble they have had with brakes. I don't want any of that. I want job and finish with on going cleaning maintenance being no problem. If that means pushing the boat out from the start then so be it.
Yes Bushy I am looking at using standard water cooled calipers and disc and then adapt them for the RS4 set up.

[Bushy]

the only other person happy with their brakes is andiroo

but i think that the sportec rims help the heat as there must be more airflow around both sides of the discs

[jeffw]

From the AP Racing web site

Brake Kit for AUDI RS4


Technical Information:

Year 2000 on Kit Part No. CP5555 - 1034
Caliper CP5555 6 Pot Disc Part Number & Size

Pad Part Number CP3700-1046/7T2,
Ø362 x 36mm, T2 Grooved, 48 Vane.
CP3894D54-DS2500.
Wheel 8.5J x 18" ET20 Standard 9 spoke


Notice that they are grooved not drilled.....

And more info
AP Racing Formula Brake Kits come supplied with large diameter discs. The ventilated discs have either 24, 30 or 48 cooling vanes depending on the application, to draw air through the centre of the discs. They are handed left and right, and are cross drilled or grooved, again, depending on the application, to allow gasses that build up on the surface to escape. Where cross drilling is used it is more restrained than on the face of our full race discs, as pad longevity is more important on a road car than weight saving. The discs are wider and of a larger diameter than standard. The extra material controls heat build up and the larger diameter means that the caliper can be mounted further away from the centre increasing the leverage effect, which increases braking torque while decreasing effort required on the pedal.
Grooved Discs : G4, G8, Grooves improve 'cleaning' of the pad surfaces and result in a more consistent brake performance. Grooved discs have a longer life than cross-drilled discs.

Radius Drilled Discs : RD, Radius Cross-Drilled discs offer improved 'bite' and 'feel', but are less resistant to cracking than grooved or plain discs.

AP Racing Formula Brake Kits use a Bolted disc mounting. Tightening torque for disc to bell mounting is also given here.

[jeffw]

This is also interesting


Brake Disc Bedding


All cast iron brake discs need to be bedded-in to ensure heat stabilisation and improve resistance to cracking. Cracks or even disc failure can occur during the first few heavy stops if careful bedding is not carried out. AP Racing recommend the following procedure:-
ROAD CAR DISC BRAKE BEDDING IN PROCEDURE
Bedding the disc from new or stress relieving the cast iron disc after it has been clamped to the mounting bell is of paramount importance if premature warping is to be avoided after the brakes are used to their full potential.
AP Racing discs are produced from the same castings as our normal race discs, but when used in the controlled area of motor sport it is easy to instruct a driver to gradually bring the disc up to working temperature with some moderate braking over a small amount of measured laps, progressively increasing his braking effort until an Engineer assess the disc visually or by temperature readings.


For road car installations the process needs to be as follows:-
For the first 10 miles, light braking from 50/60 mph down to 30 mph if possible in blocks of 5. Do not attempt any high-speed stops down to zero at this point, as only the faces will heat up with the mass remaining cool along with the mounting area. For the next 100 miles increase the braking pressures similar to stopping in traffic, again avoiding if possible full stops from above 70 mph. By now the area around the mounting bolts should be a light blue temper colour. This is a good indication that the correct heat soak has been achieved. For the next 100 miles gradually increase the braking effort after this full power stops can be used. The disc should now be an even dark to light blue temper colour, depending on the pad type and the braking effort being used during the process. This process must be completed before any race circuit use.
If used at a Track day the following points must be adhered to so as not to warp the disc.


At the start of a session use a minimum of one warming up lap for the brakes i.e. gradually increase the effort at each corner and do not drag the brakes under power as in left foot braking.


Use at least one cooling down lap at the end of the session and if possible stay off the brakes.

Do not leave your foot on the brake when parked in the paddock after a track session. If you do, the hot spot created by the pad can distort the disc in that localized area causing a high spot, resulting in vibration under braking.

On the majority of car installations, race circuit use can be more exacting on the brake system than a fully prepared race car due to the following:-
None or minimal cooling, increased chassis weight, longer braking distances due to driving technique or tyre grip.
Therefore it is very important to check your brake system thoroughly after such use. Bear in mind race cars on average cover less than 50 laps of a circuit before being serviced.

PLEASE BE AWARE THAT DISCS USED ON RACE TRACKS WILL BE SUBJECT TO HIGHER TEMPERATURES AND WEAR RATES THAN ACHIEVED WITH NORMAL ROAD USE. THIS CAN HAVE AN EFFECT ON THE LIFE OF THE DISC, ESPECIALLY IF HIGH TORQUE COMPETITION PADS ARE USED TO REPLACE THE ORIGINAL FAST ROAD TYPES SUPPLIED WITH THE KIT.
DISCS ALONG WITH PADS ARE CONSUMABLE ITEMS.

[Dave]

Does anyone else find that the holes get filled up with brsake dust and gunk??

How do you clean it out?

Dave

[Bushy]

Does anyone else find that the holes get filled up with brsake dust and gunk??

How do you clean it out?

Dave

Yep

The GMBH ones i had had the inner and outer holes offset so you couldnt jet wash them, which IMHO helped bring about their demise

The Movit ones have the holes go all the way through so weekly cleaning with the jet wash is a must

If the holes are full of dust they are efectively useless

[Bushy]

And Jeff i couldnt agree more

The bedding in is paramount on good life of brakes