# Brake Discs and pads



## Sazzle19 (Oct 6, 2009)

Hi there,

The time has come for me to replace the front and rear brake discs and pads.

I am swaying towards the Brembo Max discs. has anybody had any experience with these?

As for pads it is either...

EBC Red Stuff, EBC Green stuff or Black Diamond

Does anyone recommend one from the other?

Thanks

Sarah


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## EnfieldTT (Jun 7, 2008)

have you tried doing a search of the forum? there's been zillions of threads the last week or so about discs and pads


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## djmorton038 (May 15, 2009)

hi there Sarah.

I have just had my Brembo Max discs and Red Stuff pads delivered and they seem very well made. 
They have a good write up and there about £130 on Ebay. I am getting them fitted on Monday so will let you know the outcome. I am fitting Brembo discs and red stuff pads on the front and Mintex discs and pads on the rear with HEL lines and DOT 5.1 fluid. Cost me around £400 in total. :twisted:


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## danjones0802 (Dec 24, 2009)

i had ebc on my old car and didnt think they were all that in all honesty.

i much prefer the black diamonds


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## John-H (Jul 13, 2005)

If you are fitting discs the same size don't get ones with holes or grooves. That's the least effective way of upgrading your brakes. Taking metal away from the disc reduces thermal mass so they will reach a higher temperature quicker leading to earlier fade. Holes and grooves are largely a marketing excercise because people think they look as though they do something and the marketing departments exploit this. They were first used on motorbikes for the purpose of dispelling water off the exposed discs which is not a problem with cars. They were also effective with older pads in dispelling gasses from the interface but only at the extremes of braking when your discs were about to glow. Modern pads don't suffer the same from gassing and if you didn't remove metal with holes in the first place the higher thermal mass would mean you wouldn't be at such a high temperature. The holes don't aid cooling as evidenced by the holes being able to block up with dust (no air flow).

If you want performance the first step is to make sure your discs are not worn thin (all to do with thermal mass!). The next step to upgrade is to get decent competition pads from the likes of Mintex or Ferodo etc. (notice I didn't mention EBC) which give you a higher coefficient of friction and withstand higher temperatures without fade. Change your brake fluid to match and then if you can afford it get bigger discs which will give you more torque and cooling.


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## jbell (May 15, 2006)

Get OEM disks and Ferodo 1150 pads from John-H group buy


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## Guest (Feb 11, 2010)

John-H said:


> If you are fitting discs the same size don't get ones with holes or grooves. That's the least effective way of upgrading your brakes. Taking metal away from the disc reduces thermal mass so they will reach a higher temperature quicker leading to earlier fade. Holes and grooves are largely a marketing excercise because people think they look as though they do something and the marketing departments exploit this.


John,

Just read viewtopic.php?f=2&t=131673&p=1365497&hilit=Brake+disc+diameter#p1365407 too.

I'm looking at getting upgraded discs and pads next week assuming I am correct in that my 5 year old OEM ones are in poor shape. So many aftermarket discs from many reputable companies that I can see have holes or grooves that it surely can't just be a marketing exercise? Indeed, manufacturers of high performance cars fit drilled or grooved discs as OEM. I haven't done any estimates on this (yet) but they must be trying to claim that the reduction in the rotor's heat capacity [and frictional contact area] by removing a small amount of mass is outweighed by the benefit of having an increased surface area to dissipate the frictional heat built up. I presume that manufacturers have assessed this carefully. Having said this, I would also have thought that the biggest advantage comes from the material properties of the competition quality pads (as you infer), not small changes in the physical rotor design, especially as the rotors are vented between the inner and outer contact surfaces anyway.

There is also the claimed benefit of pad surface de-glazing from grooves. I suppose this isn't such an issue with performance pads either? We had some great discussions on night shift about this tonight with input from a knowledgeable motocyclist who affirmed what you're saying.

Doug


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## John-H (Jul 13, 2005)

Hi Doug,

There are a number of things going on here and you need to strike a balance.

Firstly, we know that renewing your old worn out discs with new ones gives a big improvement in fade resistance performance. This is due to the thermal capacity of a new disc with its increased metal mass volume. The surface area and therefore rate of cooling remains largely unaltered as the disc wears.

2mm of wear is very noticeable in this respect and a quick calculation will show you that you will be loosing about 150,000mm^3 of metal mass volume.

A 6mm hole drilled all the way through the disc would loose about 450mm^3 of metal, so dividing one by the other gives an equivalent of 330 holes. Now, you don't want to ruin the disc's fade performance with so many holes, so let's say we allow 10% reduction in relative heat capacity - that's about 33 holes - which is often what you get with some designs.

Now, the point here is that by adding holes and grooves to a disc of a given size you WILL reduce thermal capacity. By adding 33 holes you will reduce heat capacity by about 10% for starters and it's down hill from there as the disc wears thinner to 100% worn. So why do it?

Holes don't help much with the cooling as the air flows up the spirals and over the outer surface - there's not much differential pressure across the disc from inside to outside so not so much air passes through the holes as evidenced by the fact that the holes block up with dust.

The main issue with fade performance however is that the disc heats up faster than it cools during an aggressive drive, or after a long hill descent, so thermal mass is far more important in limiting temperature rise than surface area cooling during close repeated brake applications - which is where fade is going to show up.

Now, you do see holes drilled in some designs of large brake kits and there are two reasons for this:

(1) The holes and grooves give a marginal benefit at the extremes of braking temperature when the pad bonding resin starts to "gas" and form a cushion of air under the pad and reduce friction. The holes and grooves allow the gas to disperse. But this (a) only happens at extreme temperature and (b) modern pad material does not tend to do this any more so the benefit is dubious.

(2) The second benefit is that the holes and grooves cause the brake pad material to wear quicker and in the process wear off any pad glazing that may occur. But glazing only occurs at extremes of temperature.

Now you may ask why advantages (1) and (2) shouldn't be applied to standard size discs? The reason is that when you have a fixed size of disc, reducing metal mass by drilling holes and milling grooves, causes a corresponding increase in peak disc temperature for the same braking effort, due to the thermal mass reasons already discussed. They will get hotter quicker. So the problems you are trying to alleviate with measures (1) and (2) will only occur sooner - so you wipe out your advantages :wink:

With a big brake kit, the disc is so much bigger, with far more thermal mass, increased surface area and also increased braking torque for the same pad pressure, that you can afford to loose some thermal mass and possibly take advantage of (1) and (2). You can shift the balance away from heat storage to heat dissipation with a larger disc which is more useful for sustained performance around a track. But for a standard size disc, drilling holes and milling grooves is of no real value. That's why I say it's largely a marketing exercise to make you part with your money.

Upgrading your pads on the other hand to a higher friction coefficient for more braking torque and the ability to maintain that friction coefficient at higher temperatures is certainly worthwhile.

I hope that's explained things. It's worth repeating that quote from AP Racing in the link you provide:

*"Changing from a standard disc to modified aftermarket disc of the same dimensions is the least effective way of improving brake performance" *

Cheers,
John


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## paul_cymru (Mar 22, 2006)

I enjoyed that, thanks


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## Guest (Feb 11, 2010)

Hi John,

Indeed, a useful follow-up post. Thanks for that. I admit, I was probably interested more from a perspective of it looking like a nice little problem to solve in an objective way with a few simple calculations rather than using the information to sway a purchasing decision. However, it quickly becomes obvious after you've estimated the thermal mass loss that it's not a trivial matter to estimate the actual benefit of marginally increasing surface area as factors like emissivity and air dP across the disc come into play which change as speed and temperature change during braking.

I still sometimes struggle, after nearly 250 posts and over a year's membership to quickly locate specific information/good how-to's on the Mk1 section of the TT Forum and maybe newbies are finding this too, which might explain why there are so many repeat questions on popular subjects such as fitting after an market stereo. For example, I read this post and replied before seeing the more informative original post that I linked to. I don't know what else to suggest as I've found this forum to be generally excellent for providing good quality information, access to parts for sale and attitude, discipline and knowledge of members.

Nevertheless, there is still a propensity amongst some users to make bold, unsubstantiated statements on technical issues and argue black is white even when responders have taken considerable time and trouble to demonstrate otherwise. Thankfully, moderators are guarding against falling into this trap. 

Thanks again.

Regards,

Doug


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## TT Boycie (Sep 27, 2009)

I have just bought new discs and pads all round. Got these from ebay:

http://cgi.ebay.co.uk/AUDI-TT-MINTEX-RE ... 53da7b96ba

http://cgi.ebay.co.uk/AUDI-TT-MINTEX-FR ... 53db847599

£142 inc postage all in, and i must say im very pleased, a vast improvement over my last ones (not sure what make as they were already on the car)


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## John-H (Jul 13, 2005)

We certainly could do with someone creating a database of TT facts and information. In fact we could do with some that are already available pointing out.

Toshiba has done a fine job on the Mk2 forum compiling a list of How Tos: viewforum.php?f=43

I've got a few Mk1 How Tos I've done in my signiture strip: http://www.********.co.uk/ttforumbbs/vi ... 007#806007

Wak's got some very well presented material on his website: http://www.wak-tt.com/

Jim (aka Freegeek) has made a fine Wiki: http://www.wikitt.org/wikiTT/index.php? ... 7s_TT_wiki

Here's his tuner's guide: http://87.194.35.185/tt/guide/TTweakers-Guide.pdf

The TTOC have a few How Tos and there I'm guilty for not getting round to fixing and expanding it. I need to stop editing the magazine and sort it out :roll: : http://www.ttoc.co.uk/website/viewtopic.php?f=29&t=3967

As you can imagine however, the forum doesn't have its information in neat piles ready for indexing. Information is there but it's often hidden by other off topic posts of contains a mixture of facts and inaccuracies, opinions and rants. It's a mamouth task just getting rid of the swearing or spam posts sometimes. Hopefully the above will help but we need to do more.


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## T3RBO (Dec 9, 2003)

Might be an idea to get those above links added into the FAQ... it's a start :wink:


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## Guest (Feb 19, 2010)

I'm stuck at home ill so have finally got round to doing some estimates on the drilling discussion.

Assumptions: ventilated QS rotors (inboard and outboard discs each of 5 mm thickness), 312 mm [edit] outer diameter, 272 mm inner diameter, 42 drilled holes of 8 mm diameter per surface.

From this data, I estimate a 7.9% loss of frictional contact surface area through drilling with a gain of only 2.0% on emission area for radiative heat loss. In simple percentage terms, it does indeed validate the theory that the additional cooling effect of drilling is more than offset by the loss of frictional contact surface.

More to come if I can get anything sensible out of simple physics (probably best to avoid emissivity as it varies considerably with temperature and surface type (i.e. oxidised/bright/polished) and my integration is rubbish. There might be more mileage (no pun intended) in keeping it simple looking at effect on frictional heat dissipation through simple kinetic energy to heat energy conversion during braking. I think the motion that keeping the rotors solid and getting upgraded pads is well and truly carried though.

Doug


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## Bikerz (Aug 23, 2008)

Doug where on earth did you get a 332mm QS rotor from? They are 312mm :wink: 
V6 are 334mm


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## Guest (Feb 19, 2010)

Bikerz said:


> Doug where on earth did you get a 332mm QS rotor from? They are 312mm :wink:
> V6 are 334mm


Quite right. Dunno where I got it from but I wasn't overly bothered since there were other assumptions made. Anyway, post edited to take account of the difference. Answer doesn't change much in percentage terms.

I don't suppose you know the mass then so I could estimate the mass loss too? :wink:

Doug


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