8 PISTON Brake upgrade for Alfa GTA !

he doesn't have a car like yours either so would be miles behind

Well said!!!!

The major problem I find with high performance cars is that you could just be cruising on an inner city main highway at say 100km/h & there is an emergency, you hit the brakes, you stop in time but the guy behind you without the "Super" brakes, well he stops by colliding with your cars rear!!!!It's happened.

Monstro

the difference is if you didn't stop in time your insurance would be paying out, and your premium going up. if they rear end you theirs will go up... In that way bettezr than stock brakes pay for themselves...

Cheers Pud.

Yes thats a fair enough summary.

Sometimes its nice to leave real life behind though, which is why track days are so much fun

TB

Originally Posted by Pud237

TrailBraker, in response to your posts number 29 and 32 I know exactly what you're talking about. Good to see some intelligent physics on the forum

Is this a correct translation to "Layman's Terms"?

At low speeds, 330mm and bigger brakes could both lock the wheels, so you would have to press the pedal to generate just less than the force needed to lock the wheels to achieve maximum braking potential. Here, the driver skill at modulating the brake pedal is more important than the size or potential stopping power of the brakes.

At higher speeds, however, when neither system has any chance of pulling enough negative g's to lock the wheels, the bigger/more powerful the set of brakes you can get the better. Obviously, in real life when finances are limited, once you get to a certain point getting a better system becomes far more costly, for a performance improvement you are unlikely to ever need.

I couldn't explain Better. You got the feeling Monstro. Thanks.

Is like you try to describe the beauty of a stunning woman to someone who is away. No numbers can tell. No words can tell.
He has to see with his own eyes.

Originally Posted by GTAFAN

I couldn't explain Better. You got the feeling Monstro. Thanks.

Is like you try to describe the beauty of a stunning woman to someone who is away. No numbers can tell. No words can tell.
He has to see with his own eyes.

To me, car's were nothing compared to women. Until I bought an Alfa

Nothing like a temperamental Italian beauty to stir the soul

We can all agree on that

Originally Posted by Trailbraker

Brakes work by transferring kinetic energy of the moving car into heat.
My point is that I believe the brakes simply wouldn't be able to generate enough retarding g-forces when braking from 245kph to lock the tyres - since the amount of kinetic energy that has to be dissipated is hugely more than for lower speeds.

i.e. From my simplified little chart in the post above it takes 5 times as much "work" to decellerate from 245kph to 215kph as it does to brake the same 30kph from 60kph to 30kph.
i.e . the brakes are having to work 5 times harder at the higher speed compared to braking the same 30kph at a lower speed - thats a lot of extra clamping requirement!


Many (all) cars could lock their tyres at 30kph, not many could lock them at 100kph, and I'm fairly sure even a McLaren F1 might have issues locking its brakes at 245kph!

I can imagine that it doesn't feel like this with your very rearward brake bias though? I think this probably just proves the importance of correct brake bias, which is what we all have been agreeing on
I can absolutely stand on my DS3000's at 100mph and would only be beginning to pick up ABS effects at about 40-50mph'sih .

As you say : it is the case that the brakes wouldn't be able to pull more than 1g for good road tyres, but what I amsaying is that at high speeds "smaller" brakes wouldn't even be able to get close to contributing 1g decelleration.

As an aside : wind resisted decellerative effects act on the body of the car as opposed to brakes that ultimately act through the tyres.
It could well be the case that the actual physical decelleration of the car is greater than 1g in any case when wind resitance is taken into account.
This doesn't really affect the argument in relation to tyres since not all of this (> 1g) force is acting through the tyres and I would submit that the *brakes contribution* would be less than the road tyres limit at high speeds.

Hopefully some of that made some sense to somebody

Cheers,
TB

I completely understand all of the above, and I am not sure at how high speeds (to take an example) the braking system on my blue car is able to lock it's wheels. But i do know from own experience in that car, that when you are driving without ABS in the wet or under anything less then optimum circumstances, f.ex if suspension is not 100% stabilized, lock-up can happen at surprisingly high speeds. I have had the front wheels lock at about 190 km/h.

Going back to the point about Brake Bias which it seems I am not having any success in getting anyone here to understand or pay attention to.. I found an article on that Stoptech site. It's a good read and explains in great detail what happens when you increase the caliper piston bore while keeping stock Master brake cylinder.

Incidentally i talked in lenght on this subject to a Porsche Racing enthusiat earlier this week when i was doing a factory tour at their plant in Zuffenhausen. Aparently Porche drivers calculate with as much as 45-50% braking taking place at the rear That alone makes a significant difference in terms of potential stopping power when compared to our cars where about 80% of the braking takes place at the front.

He reckoned modern high performance cars with mid or rear mounted engines would always be able to outbrake any front engine mounted car no matter how big you make the brakes. He also noted that a FWD being the more extreme example with the most front Biased brake set up since the centre of gavity is pushed so far forward. (no diferential/drive shaft adding weight to the rear) He also thought that the ABS could very well be operating at full capacity without any input being felt in the brake pedal since the ABS when operating at very high speed is tentatively modulated not to upset the balance.


Anyway the below makes an interesting case, the question being if this applies to the Bosh 5.7 ABS system with are standard on all GTA's and GT 3.2's

-----------Snipped from Stop Tech ----------------

ABS Control In Super-Slow-Mo
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level - from the processing algorithm's perspective.
Say you are driving down the highway at 75 MPH (the posted speed limit, of course) when all of a sudden the truck in front of you spills its load of natural spring water across all three lanes of traffic. Now, this alone would not be so bad, except the water is still sealed in 55-gallon drums - one of which would certainly make a mess of your car's front fascia. Time to take evasive action.

Being the trained high-speed individual that you are, you immediately lift off the gas, push in the clutch (you are driving a manual transmission, right?), and simultaneously nail the brake pedal...but in the heat of the moment you hit it a little too hard.

Meanwhile, the ABS is hanging back watching the world go by, seeing a constant stream of 75 MPH signals from its four wheel speed sensors. Let's call this "observation mode." Upon your application of the brake, however, the ABS snaps to attention, its antenna up, ready for action. You have just hit the brake pedal after all, and who know what's coming next.

After 50 milliseconds (it's actually much faster than that - 7 to 10 milliseconds is typical - but it makes the math easier) the ABS takes another snapshot of the wheel speed information in an attempt to figure out what's going on. This time the wheel speed sensors are all reporting a speed of 74 MPH. Doing a quick calculation, the ABS determines that in order to have slowed 1 MPH in a 50ms period the wheels must be decelerating at a rate of 0.91g's. Because you are driving a sports car, the engineer who calibrated the system 'taught' the ABS that your car is capable of decelerating at this rate, so the ABS continues to hang back and watch the event from the spectator's booth. No problem so far.

The next 50ms, however, are a little more interesting. This time around, the wheels are reporting 72.5 MPH. Now, it may not seem like a big jump, but to slow 1.5 MPH in a 50ms window equates to a deceleration of 1.36g's. Not alarming, but the ABS 'knows' that based on this deceleration level, the wheels are probably beginning to slip a little more than they should - after all, your car is probably not decelerating at quite 1.36g's..and any error between the two indicates slip.

ABS is now in "ready mode." It's probably too soon to jump in, as the wheels might spin back up on their own in the next 50ms loop, but things are definitely looking bad!

As the first barrels of spring water bounce left and right, missing your car by inches, you stay on the brake pedal but push even harder. This time around, the left front wheel speed sensor is registering 68 MPH - a 4.5 MPH drop in the last 50ms, or a deceleration level of 4.1g's. Doing the math faster than you can (after all, you are busy dodging barrels of spring water), the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error.

So, based on a wheel deceleration of 4.1g's, a slip level of 5% (3.5 MPH 71.5 MPH), and a couple other factors not listed here, the ABS jumps in and enters "isolation mode." (Note that the wheels are nowhere even near "wheel lock" - the 100% slip point.) The first thing the ABS does is shut off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure - after all, it was the driver that got us into this mess in the first place.

Next, the ABS starts work in "decrease mode," releasing the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Since the ABS knows how quickly the wheel is decelerating (4.1g), how fast the car is actually going (71.5 MPH), and the pressure-torque characteristics of the left front caliper/pad/rotor assembly (we'll come back to this one in just a second), it can precisely calculate how long to open its release valve to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts).

Let's say that calculated time turned out to be 10 milliseconds (this again makes the math easier later on). Bang! Valve opens, pressure is released, and 10ms later it closes, leaving just the right amount of pressure in the caliper so that the wheel spins back up to exactly 71.5 MPH, but continues to decelerate at 1.0g. Everything is going as planned.

Time to close the loop and enter "increase mode." Once the ABS sees that the left front wheel has returned to near the 'real' vehicle speed, it slowly reapplies pressure from the master cylinder to make sure that maximum sustainable brake force is being utilized. To this end, the ABS calculates precisely how long to pulse open the isolation valve, slowly building pressure at the left front caliper until once again the left front wheel begins to slip. It performs this calculation based on - you guessed it - how quickly the wheel is re-accelerating, how fast the car is actually going, and the pressure-torque characteristics of the caliper/pad/rotor assembly.

In our hypothetical little world, the ABS calculated that four pulses of 5ms each were necessary to build the wheel pressure back up to the point that the wheel began to slip again, returning to "isolation mode."

The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop. Hopefully, this did not include punting a spring water barrel or two along the way as the ABS kept all four wheels slips in the 5%-10% range, allowing you to turn and swerve to your heart's content as the drums bounced out of your path. Happy car, happy driver.

The Potential Impacts Of "Big Brakes"
Let's now take the exact same scenario, but add a twist: you are returning home from having that long-sought-after big brake kit installed. You know, the one that required new 18" wheels to clear the 8-piston calipers and 16" rotors. Driving around the parking lot you couldn't believe the improvement in pedal feel and initial bite they displayed. These things must really throw a boat anchor behind the car at high speeds, right?
Well, let's see
Resisting the temptation to run in the fast lane at triple-digit speeds, you once again find yourself behind the spring water truck at 75 MPH. Barrels fly and you again lay on the brakes, but with the increased confidence of your new hardware to slow you down in time. Plus, you now know how the ABS works, so you lay into the pedal, confident that you will have both deceleration and steerability. It couldn't get any better.
Like scenario 1, after the initial 50, 100, and 150 milliseconds the ABS takes snapshots of the wheel speed information and registers 0.91g's, 1.36g's, and 4.1g's on the left front wheel. Again the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error. So far, so good - just like last time.

Here's where things start to get interesting, though. ABS enters "isolation mode" and shuts off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure. Next, the ABS starts work in "decrease mode," and once again calculates that 10ms are required to the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Unfortunately, this calculation was based on the standard vehicle's pressure-torque characteristics of the left front caliper/pad/rotor assembly. Let's talk about this briefly while the barrels roll in closer.

Pressure-Torque And Pressure-Volume Relationships
When a braking system is designed and installed, the components are chosen to provide a certain deceleration level for a certain amount of force applied by the driver to the brake pedal. While the overall relationship is critical, there are many ways to achieve the same end…but fundamentally the parts are chosen to work together as a system.
One of the most important relationships for the ABS engineer is the pressure-torque (P-T) relationship of the caliper/pad/rotor assembly. In so many words, for a given brake fluid pressure, X, the caliper/pad/rotor assembly will build up a certain amount of torque, Y. For the sake of argument, let's assume that adding 100 PSI of brake pressure to the stock caliper in our example vehicle generates 100 ft-lb. of torque.

Another important relationship is the pressure-volume (P-V) characteristic of the system. This relationship defines the swelling or expansion of the brake system for a given increase in pressure. Let's also say that our stock vehicle brake system 'swells' 1cc for every 100 PSI.

Unfortunately, there are several big-brake systems available today which pay no regard to the original P-T or P-V relationships of the original vehicle…and in fact many make it a point to affect drastic changes in these relationships in order to give the consumer that feeling of 'increased bite.' While the upside is certainly a firmer pedal and higher partial-braking deceleration for the same pedal force, the trade-off can be ABS confusion.

Back To The Barrels
So, back to our example - the ABS has just calculated that a 10ms pressure reduction pulse was necessary to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts)…but the new system with its decreased P-V characteristics (increased stiffness!) releases twice as much pressure as the stock system in the same 10ms window (the equivalent of a 20ms pulse with the stock system)! Of course, the increased P-T characteristics (bigger rotor! bigger pistons!) don't help either, as now three to four times as much torque has been removed from the wheel as with the stock system, leaving only enough torque to decelerate the wheel at, say, 0.3g. In ABS land this is known as a 'decel hole' and feels just like you momentarily took your foot off the brake pedal.
Now, given that huge pressure decrease, the ABS quickly enters "increase mode," trying to correct and build the pressure back up near the vehicle's maximum sustainable brake force. This takes time and time equals lost stopping distance.

The ABS calculates precisely how long to pulse open the isolation valve and determines that four pulses of 5ms each are necessary, just like before. Because of the new P-T and P-V characteristics however, after only two pulses the wheel is again being forced into slip, leaving the ABS scratching its head and wondering what's going on. Not expecting wheel slip so soon, the ABS quickly releases pressure in an attempt to recover, but the damage has already been done.

The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop…but this time the ABS is always one step behind. In some cases the ABS is robust to modest changes in the base brake system, but in extreme cases there can be a significant negative impact to the vehicle's steerability (increased front wheel slip due to poor control) and a measurable increase in stopping distance (multiple 'make up' decrease pulses).

So, your chances of stopping in time or swerving to avoid one of the bouncing barrels have been decreased. In this game, inches count and you sure need every one.

TCS/ESP/EBD Impacts
The analogy above translates directly to the TCS/ESP/EBD subsystems without exception. Like the ABS, these three technologies rely heavily on the P-T and P-V characteristics of the OEM system, and any changes can manifest themselves under braking, accelerating, or dynamic maneuvers.
Are You Telling Me That Big Brakes Are A Bad Idea?
So, will all big brake upgrades wreak havoc on the chassis control systems found on your favorite ride? Not necessarily. In fact, if designed and chosen properly, these upgrades can make the most of these control technologies while providing all of the cooling and thermal robustness advantages these kits have to offer.
The "secret" to brake system compatibility is that there is no secret - it just requires fundamental engineering expertise and design know-how.

As mentioned earlier, far too many of the big brake upgrade kits on the market today pay no attention to the P-T or P-V characteristics that the car originally possessed. In fact, there are kits available today which have P-T characteristics which more than double the output (P==>2T) of the stock systems they replace - "200% More Stopping Power" must be better than stock, right?

In most cases, these vendors procure large quantities of big rotors and red calipers, fabricate an adapter bracket to mount them to a variety of different suspensions, and market the kit as a 'one-size-fits-all' without first determining if the system will be compatible with the remaining foundation braking system, let alone the electronic chassis controls. Sure, it's quick, cost-effective, and looks like a million bucks through your 18" wheels, but what about ultimate performance?

The Solution
Unlike the "if it works on brand P, it must work on your car" approach, at STOPTECH all brake upgrade kits are designed with the characteristics of the original braking system taken into account to minimize these differences. This is the reason that when you order a STOPTECH big rotor upgrade kit the new caliper bores may actually be smaller than the units you are replacing to "balance the equation." This is just one way in which our engineers attempt to retain the original system's P-T and P-V integrity. Sure, it's not one-size-fits-all, but neither is your car…or your driving style. Why should you expect any less from your brake upgrade?
In closing, next time you think about bolting on those 16" rotors and 8-piston calipers remember that there are a number of chassis control systems out there just waiting to be confused. Select wisely and reap the benefits

Originally Posted by Peter K

-----------Snipped from Stop Tech ----------------

ABS Control In Super-Slow-Mo
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level - from the processing algorithm's perspective.

That is a very interesting article indeed - thanks for posting.

Nice info Peter. Thanks

The Porsche guy Is 100% correct. They can use in their cars up to 40%-45% of braking on the rear brakes, because they have special developed systems for that.
Now the Question is hoW can we increase the rear baking work in our cars? We can not remove the ABS unit but work with that and understand how it works.

And OUR ABS WILL INCREASE THE BRAKING UP TO 30%-40% IF WE PLACE BIGGER BRAKES REAR .
How difficult is to understand that?
Try it and you will see.

When I brake in the city on low speed I get the feel that my system is braking more on the rear than the front. Because on low speed (30km, 40km,60km ) the car stops easy without the need of the front system to work- or work more than the rear. And that happens because our (GTA) ABS unit starts braking from rear.

Gents this is not theory. This is pure facts. And is working every day to my car.

What is the point of 30-40% rear braking bias on a FWD nose heavy car like the GTA?

Before you fly off the handle and tell me to "trust" you again. please observe the following which i think even apply to those select Phantom GTA's of Greece and South Africa..

The weight distribution of 156 GTA is 64,5/35,5 The 147 is 66/34 plus the shorter wheel base of the 147 adding to greater dynamic weight transfer compared to the 156. So it's safe to conclude the 156 will have the best deceleration potential of the two.

Lets take the 156 as an example using the kerb weight of 1410 kgs. Static weight distribution is 909 kg front axle, 500 kg rear axle.

When braking at 1 G and assuming you have resonably well proportioned fast road geometry and suspension settings, you are shifting about 60% or 300 kgs of the initial static rear axle pressure to the front. That leaves only 200 kgs or roughly 14%.. In other words the optimum brake bias for the 156 at 1 G is roughly 86/14..

I'd very much like to discuss dynamic weight transfer via suspension and Geometry tweaking.. TB and I covered this ealier here on AO in another thread, but i forget which.... I know to some extent how much weight you could expect to shift via coil overs (hight) and via altered spring rates. All this of course done while keeping the car very track oriented..Everything is a compromise..

If you guys GTAFAN of Monstro could share any data on the Geomtry and suspension settings you have now or plan to run with, that would be really helpful.

If your car GTAFAN, -is set with a 30-40% rear brake bias, there must be some very radical changes done to these parameters to compensate for the dynamic weight transfer... From theory is should not be efficient (or safe if no ABS) to brake with a GTA with that kind of rear brake bias.

Thats exactly the point.
Because we have heavy front cars, if you can brake more on the rear,
you remove more weight from the front brakes-suspension-tires to cope. And that is better braking and less possibilities to lock the front wheels.