Polo 6R braking thread (Mainly GTI/Diesel)

[gavs]

Ok, I've been planning on writing something up for a while for my fellow 6R owners out there in regards to brakes and braking, so from a couple of earlier posts I have written in other threads, I will try to compile it all in the one location.

So, to start with....

---------- Post added at 12:58 PM ---------- Previous post was at 12:51 PM ----------

Ok, now to try and explain the principles of braking using my simpelton knowledge

Brakes are heat generators. They do this to turn your kinetic (moving) energy into heat energy which gets dissipated into the atmosphere. How? Your pads creating friction against your rotors.

That's the simple answer. The biggest enemy of your brakes is heat. Because they are heat generators, the hotter they are initially, the less heat that they can dissipate, therefore it takes you longer to stop. This in turn affects your pads. If the pads have a heat limit of say, 300 degrees C, then after that temperature, you start getting a longer stopping distance because they are starting to break down and are no longer in their operating range, therefore you go to a higher temperature level in your pads. How does different brake fluid help? Well, there are 2 reasons:

1) Brake fluid, like any liquid, has a boiling point. Due to the heat generated by using your brakes, this heat in turn gets transmitted through your calipers, back into the fluid. Again using 350C as an example, if water boils at 100C, this example fluid boils at 360C and your pads are no longer in their optimum range at 350C. This means that they are hotter than this when you go to stop, elevating their temperature to 370C. Remember, the brake fluid boils at 360C, so it is now boiling and turning to vapour in your brake lines. The pressure which is generated in the system when you put your foot on the pedal is sufficient to pressurise the fluid which squeezes your calipers onto the rotors, but it is not enough to compress the gas (vapourised brake fluid) in your lines as gasses need much more pressure to be compressed. This results in a "long pedal" which you might have heard of before. After being boiled, your brake fluid is never the same again and will have a constantly decreasing boiling point.

2) Again, with the temperature, but from a different perspective. Brake fluid is hygroscopic, meaning it absorbs water and eventually as it reacts with air (it takes a fair while!) but it can break down into water. This is bad because as shown in the example above, if you have any water in the system (and it can seep in over time) it boils long before the fluid, but because water has gotten into the system, your brake fluid itself is breaking down into water, so just 1 drop in a sealed container can destroy the fluid. So, if you standard fluid boils at (again) 360C, yet a Race fluid boils at 800C, the amount of water that renders your 360C fluid useless wont render your 800C fluid useless for a longer period of time. Race fluid is also engineered to withstand more extreme heat loading and cycling so it is far less likely to break down as readily, hence the $30 price difference to standard Castrol Dot 4 stuff.

---------- Post added at 01:00 PM ---------- Previous post was at 12:58 PM ----------

That as far as I know is the fundamentals behind braking regarding disc brakes anyway, don't ask about drums because I have no idea! What about cross drilled and slotted rotors, cross drilled rotors, slotted rotors etc? Well, there are 3 fundamental thoughts behind this.

1) Cross drilled. The thought is that under braking, your pads produce gasses due to friction against the rotor, which they do, but to the levels that adversely affect your performance, you are really going to struggle to get to that point..... The drilled holes supposedly let this gas escape into the ventilated part of the rotor, yet remove surface area and weaken the rotor (have a close look at an old drilled rotor and notice the cracks around the holes...)
Slotted. Again, same principle to remove gasses from between pad and rotor, yet vent to the outsides of the rotor. Again, material is removed resulting in less surface area, but the rotor is not weakened as these slots are generally cast into the rotor.
Combo of both. Honestly, these rotors do both? Give me a break....

2)
This, is a brembo F1 brake disc, see any slots or holes?....... Brakes (as mentioned above) are to dissipate energy through heat. The greater swept area of the rotor in contact with the pad during braking, the greater amount of energy can be removed as heat. This is also another reason to go to a bigger diameter, they won't decrease your stopping distance, however they are able to dissipate more heat over a broader area, therefore you are less likely to generate heat-induced brake fade.

3) Now, as a designer, I have spoken with a few engineers and fellow designers in the automotive field in my time. The reason they give me for cross drilling/slotting rotors? It's a simple one, looks. Cross drilled rotors and slotted rotors look cool, it's as simple as that. One designer who works for the VW group said that when he was working on the 977 lineup of Porsche GT series 911s, the engineers designed the carbon ceramic brakes for them, but they looked hideous, so the decision was made to cross drill them, so they looked cool, like they were actually worth the $25,000 premium.

So, on that note,I will be sticking with the standard rotors, just upgrading the pads and fluid

I hope that helps you guys in making some decisions

---------- Post added at 01:18 PM ---------- Previous post was at 01:00 PM ----------

So, after all that, how about some info on brake lines and some common misconceptions.

Misconception 1: Braided brake lines decrease stopping distance.
Ah, no. Braided brake lines have the benefit of not having the same initial flex that a rubber one would have once the pressure of braking is introduced into the brake line. Rubber brake lines do indeed swell slightly once pressure is introduced, this is true but it doesn't increase your stopping distance. What braided lines do however, is increase pedal feel and feedback. This is awesome for those of us who like taking our vehicles for a good hard mountain run and we can feel the pressure change when fade starts setting in, but not on a 6R. Why? I'll get to that...

Misconception 2:
Braided brake lines increase braking performance.
Not really, again, it comes back to pedal feel, again also, somewhat irrelevent in a 6R. For the ever so slight chance of a teeny weeny increase in braking performance from buying braided brake lines, put it towrads better, stickier tyres for the front of the car. These alone will provide such a big improvement, you will laugh about the day you nearly wasted your money!




Ok, so why are certain things irrelevent on a 6R? Simple. Control module 03, 10 Adaptation, 09: 0, 1, 2

This code alone is what controls your braking. In the 6R, your braking system is 90% identical to any hydraulic braking system except for one thing, the brake pedal itself. It is connected to the braking system as normal but to generate brake pedal "feel" and application ratios of pedal pressure vs caliper clamping pressure, it is connected to a box full of 1's and 0's that sends coded signals to another box that controls the brake master cylinder. I have personally found that the only difference in brake feel that I can get is once the pads I have are up to their prefered operating temperature, but by "feel" I don't mean the feel through the pedal because that resistance doesn't really change (it's probably more a placebo effect), the feel I get is through the rate of deceleration and when a certain amount of pressure applied gets a better/worse result, depending on temperature.

SO, with that section of coding, 0 is the factory default for brake distribution, 1 is midly worse, 2 is windscreen-headbut material. It changes the amount of pressure that the master cylinder applies dependant on pedal travel. It basically removes any modulation of the pedal that you have to give maximum braking performance. Good on the track, probably not quite as good when you need to modulate, especially in peak hour traffic!

The next post will be in regard to upgrades. What you can / cant do, what some costs are, and hopefully some attempt at technical info

[iigx]

Nice info! Brain annurism aside, i'm interested to know now if its worthwhile putting the racing brake fluid you mentioned with a higher boiling point into my GTI?

[Ryan_R]

Thanks for the write-up

[RoknRob]

Yeah, seriously great piece. Thanks for taking the time.

Looking forward to the rest!

[gavs]

Nice info! Brain annurism aside, i'm interested to know now if its worthwhile putting the racing brake fluid you mentioned with a higher boiling point into my GTI?

The first day I had my GTI, I cooked the brakes, (yes, after bedding in properley etc, this will be a later topic...) so I believe that it does make a considerable difference.

[mythik]

In the 6R, your braking system is 90% identical to any hydraulic braking system except for one thing, the brake pedal itself. It is not connected to the braking system, it is connected to a box full of 1's and 0's that sends coded signals to another box that controls the brake master cylinder.

[gavs]

Otay, everybody's brains still working ok? Good

Upgrades. Well, this is quite probably the most sensitive issue regarding brakes because you can fork out some really serious cash for brake "upgrades" in the form of 6 piston calipers with 425mm cross drilled and slotted discs (do we remember why these are pointless?) all around, braided brake lines and then, you find your 0-100 braking distance has shortend by 1 whole meter! Woooo! my $12,000 just got me 1m extra performance!

Put simply, a wise man once said to me "The best braking package you can have is the smallest you can get away with, without compromising performance."

So, with that in mind, aside from the previously mentioned pads and fluid upgrades, what can we, as 6R polo owners look at? Well, I'll start with the other petrol powered models first, the 1.4 and 1.2TSI models.

First, if you want to go at all bigger, you need these:


These are the front spindles off any VAG car that runs the bigger, sliding caliper setups including TDI and GTI 6R polos. These do not have the carriers for the calipers, so you can bolt on the bigger carriers off the TT, you can bolt on some 4 piston porsche clipers, hell, you can go for these bad boys!

So, now that the other models are up to TDI/GTI spec....

The TDI has the same braking package as the GTI. Why? The extra weight over the front axle of the diesel engine. The less powerfull models make do with the Mk4 Golf standard brake package of 256mm vented front rotors and 232mm solid rears. The GTI goes up to the 288mm front ventilated rotor, the bigger 2205square mm piston, but retains the same rear discs and caliper, albeit in red (so more betterer).

Not only are these the same brake calipers as on the Mk5&Mk6 Golf GTI, but they're also the same as the last polos and the audi TT. We like this, because it opens the possibilities for some upgrades that are not only off the shelf, they are direct bolt-on options that have come from the VAG factories around the world.

So, to be more 6R specific, here are some figures to consider. The 6R GTI weighs 1189kgs, with a maximum front axle weight of 930kgs. This is interesting because the previous Polo GTI had a maximum front axle weight of 960kgs, yet ran the same braking package. So, while the 6R is slightly heavier, the weight balance is further back in the car, so theoretically, a better balanced car, we have. This bodes well with the considerable accelerative performance and terminal speed increases, especially with how these cars effortlessly pull to 200 quite comfortably.

So, with this in mind, what can we do in regards to bigger brakes? the first stop, is these:


These, are 312mm front discs off an Audi TT / Mk4 Bora 4Motion. To fit these, you will need the bigger carriers that fit the 312mm discs. The calipers used on these larger discs, are identical to the GTI/TDI, the only difference is the carrier and disc itself. The benefit you will get in braking performance is that your cooling surface area is increased and the "handle" region of where the pads grab the disc is further away from the axis of rotation. This setup though, poses one problem, increased weight. The increase in weight alone might be enough to outweight the advantage gained from moving the handle point further out, but the cooling efficiency of your disc will still be better, so it could be a good solution. to get the best out of this upgrade, lighter wheels or 2 piece discs with an allot top-hat will benefit with reducing the unsprung mass. hell, you might even end up being lighter than stock!
What about the rears? Well, with this setup, you shouldn't need to alter the size of the rear brakes. a) because of the limited power they submit but, more importantly, b) the TT runs this identical setup. 312mm fronts, 232 solid rears. If you want better cooling performance on the rears, you can look at aftermarket ventilated rotors, these will also reduce un-sprung mass in the rear of the car.

What's next? well. In my opinion, to not upset the balance of the braking performance of the car, from her on out, you really should do fronts and rears together, trying to maintain the same braking ratio ~70%front, ~30% rear. To do this, you can buy upgrade kits that are bolt ons from the VAG range, or go aftermarket.
Some aftermarket setups include Alcon,Tarox, or, for an "aftermarket with VAG flavour", you can look down the road, to the company the grand-daddy of the modern VW has named after him...
Porsche.

Porsche brakes can almost bolt directly on. The beauty of these kits though, isn't in the name, but in the wide range of pads that you can get for them as they are a factory setup. Nearly every (if not every) aftermarket pad manufacturer makes pads for the Porsche lineup including EBC, Hawk, PBR, Remsa, I'm sure even QFM make pads for Porsche brakes! So with that in mind, my pick would be these:
Volkswagen Golf IV 1.8T > Braking > ECS Stage 2 > ES#1171 Big Brake Kit - Red Caliper - Cross Drilled & Slotted Rotors (312x25) - MK4S2BBK-RXS
These, are 4 piston calipers off a Boxster and fit the 312mm brake discs. Not only do you limit the weight increase by keeping the disc size under control (and off the shelf which is handy! They can keep the cross-drilled and slotted rotors though) the calipers are generally an aluminium alloy which is lighter than the factory single piston jobbies, but the clamping pressure from the caliper is more even across both sides of the disc, as well as increasing the swept area of your pads by having a bigger pad. Not big enough? Well, like I said earlier, you can go crazy-stupid with the 6 piston, Cayenne turbo brakes, but what for other than looks. The maximum that I personally believe you would need, are these:
Volkswagen Golf IV 1.8T > Braking > ECS Stage 2v2 > ES#1180 Big Brake Kit - Red Caliper - Cross Drilled & Slotted Rotors (332x26) - MK4S2V2BBK-R XS
Your handle point is moved a further 20mm out but at this point, you have to consider the weight factor again. For this kit especially, you really should be upgrading the rear brakes too.

Next time, bedding in and how it can completely change not only how your brakes work, but how effective they are at doing what they're intended purpose is.

---------- Post added at 02:04 PM ---------- Previous post was at 02:03 PM ----------

Wouldn't worry about it, most modern cars are the same, the throttles are the same too...

---------- Post added at 02:13 PM ---------- Previous post was at 02:04 PM ----------

Some 6Rs with different brakes...

[Buller_Scott]

wow gav, bloody nice write up! great information for those who want something more, but dont really know how it all works

big brake kits aside, to anyone who's wondering - YES, uprated pads and fluid will do wonders for your car - i have the TRW race fluid in my car, and i cannot stress enough, just how confidence inspiring this is - the brakes have never faded on me on heavily spirited runs in the hills...

i've been there before - brakes fading after 6 corners downhill, understeering wide and shtting my pants, hoping that i dont crash. never again.

[iigx]

Scott, can you link/detail the specific fluid you use? Also i assume you have to bleed it in, and its not simple.

As far as changing the brake pads, i assume this is a relatively complicated process for someone without a workshop to play with - or say a $300-400 labour task for a 3rd party?

[gavs]

iigx, Greg at GLS Rallysport (the stockist for QFM pads) sells the TWR fluid at a really decent price. Yes it involves bleeding and flushing the lines, but it really isn't a big job. If you jump on ECS tuning, you can actually by the motive power bleeder which is hany if you do it on your own, for around $50. The pads, the only difficult thing is the handbrake cable on the rear caliper. If oyu have a piston wind-back set, then it's a piecce of cake, really. I have the service manuals if you want to take a look and if you do do it yourslef, you will kick yourself as to my you have ever paid anyone to do it for you!

Scotty mate, there is more to come! Stay tuned