8 PISTON Brake upgrade for Alfa GTA !

Originally Posted by Monstro3.7

Glenwood Motors told me that from the experience running in the present Monster Touring Cars with a 156GTA 3.7 that the optimum brakes are 365mm at front with a 6 piston or better caliper & 305mm at rear with a 4 piston unit.
Monstro

@Monstro and GTAFAN.. I am sure that Glenwood motors and the Greek based "Brake technician" know their stuff, but there are some problems in the way you percieve or pass on the information you get from them..

When Glenwood motors tells you that the optimal brakes are 365mm 6 piston & 305mm 4 piston, then this is in no way a universal rule.. The effective brake torque of such a "combo" is not static!

So they must have had a much more particular system spec in mind when they told that this combo is what they had the best experience from.

Irregardless of how sophisticated the Bosch 5.7 four channel system is, you still have to go back to square one..The mechanical pedal ratio is static and can not be changed unless you change the hardware..

You have to ofset bigger brake discs by decreasing the effective clamping force.. This is easiet achieved by smaller pistons.

When i read you fit bigger discs and bigger calipers with bigger pistons, i know with great certainty that you have drastically increased the effective clamping force. If you do not even out the bias by fitting matching bigger brakes to the rear, then you will be moving the brake bias forward (or rearward if you go too big at the rear), which effectively means stopping distances can go up quite dramatically..

The question is, does your system balance the brake bias to optimum, and how is this achieved? You have to consider that it's far from the brakes alone which transfers weight rear-to-front..Pad compound, suspension and chassis plays a huge factor to effective brake Torque output.

With all this in mind, and knowing that the 330mm system outperforms street tires and possibly R-tires i have to say once again that i can not from any scientific point of view see why bigger brakes will automatically stop your car quicker..

Better balanced brakes will stop the car quicker..and better balance could in theory be acieved by tweaking suspension alone.

In the end It starts and stops with the tires.. brakes dont stop the car, tires do.. how is potential 1.4 g braking torque better then potential 1.2 g braking torque on a 1.1 g tire?

the green eyed monster rears its head again I see....

Originally Posted by ukoldschool

the green eyed monster rears its head again I see....

A bit more friendly would be appreciated.

This is true to an extent, but not at track type speeds I think.

I don't know if you or others have been reading the Stoptech brake site that cleverly wants to explain why they actually can't produce front brakes kits that brake harder than standard.
They (somewhat disingenously) claim brakes are all about thermal tolerance and keep the front effective brake effort the same as oem.
They then point out that they don't supply rear brake kits, unlike their competitors (who of course must be misguided).

The point I believe the Stoptech marketing people are intentionally ignoring, is that while braking from higher speeds the 1g road tyre limit would not really be reached since the decellerative work that the brakes have to do is proportional to the square of the velocity (Kinetic Energy= 1/2 M*Vsquared).

Braking from 60kph to 30kph = 2700 units of energy i.e. ( 60 * 60 ) - (30 * 30)
Braking from 120kph to 90kph = 6300 units of energy. i.e. (120 * 120) - (90 * 90)
Braking from 245kph to 215kph = 13800 units of energy. ie. (245 * 245) - ( 215 * 215)

So while the useful max braking effort for road legal speeds in most countries can probably be fairly efficiently handled by oem brakes, once you get to higher speeds the tyres aren't at their decellerative limit under full braking since the brakes can't do the work required.

Cheers,
TB

Originally Posted by Peter K

In the end It starts and stops with the tires.. brakes dont stop the car, tires do.. how is potential 1.4 g braking torque better then potential 1.2 g braking torque on a 1.1 g tire?

Not sure what you are saying there TB.. How is it not possible to lock the wheels at 245 km/h ?

My Rear brakes.
Porsche GT3 calipers with sport ceramic pads and 305mm disks.
The ALU adapters are from airspace aluminum. Piece of art design.
These calipers are from the strongest rear with the ability to take from
300mm -380mm disks. Is not easy to make with the right angle since they have two different size shoes and 156 rear system
has a lot of moving parts.

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

Originally Posted by Peter K

Not sure what you are saying there TB.. How is it not possible to lock the wheels at 245 km/h ?

TB good point.
You are right about hi speed braking.
From my experience I had to brake many times from 250km to 120km
and some times from 270km. I never locked my tires.
And that proves that bigger or even huge brakes are never useless.

The issue is that I hardly remember to lock my tires even on small speed braking. Maybe one or twice on very slippery roads.

And I dont remember at all when was the last time my ABS come to work in my car. Even when I had the Big Maranelo calipers at the front.

The ABS is actually very good on the 156 GTA I think, even for track driving, it really delays as long as it can before coming on IMHO.

I really rarely experience it much, normally its when my tyres are overheating at the end of a long track session and I am braking like mad for a hairpin.

Nice but lose the prancing horse center caps, they're pretentious as ****, it's an Alfa your driving after all

May be that's explain why I have got the plug behind my brake disc but no cable attached.

Originally Posted by GTAFAN

TB good point.
You are right about hi speed braking.
From my experience I had to brake many times from 250km to 120km
and some times from 270km. I never locked my tires.
And that proves that bigger or even huge brakes are never useless.

So now your mildly modded GTA does 270 km/h..and you casually slam the brakes from those speeds?

Is that Penn & Teller calling?

Yes my friend! My GTA goes easy to 270km.
When we meet there, prepare a good GPS and I will take you with me
to see of your own. And then we will hit the brake pedal to count the
negative G force.

I had to brake from that speed many times when I was on a big highway and some big tucks were trying to overtake other.
When you come behind with that speed they hardly see you on
the mirror and you are behind them on a few seconds.

surely if your doing 270kph on a public highway its not bigger brakes you need but some common bloody sense. i thought you were using it on a track!

In Greece it's still possible to do these speeds & under safe low traffic density conditions. Check on the web, the Attika highway was voted best in Europe. I drove GTAFAN's car, 4 up & as you recall GTAFAN, my wife had her Garmin GPS & she was checking the speedo. I drove at around 210-240km/h, effortless, 4 up, hit a couple of 250's indicated & your speedo was 4km/h out. So an indicated 270 is a genuine 265.Drove the car, witnessed it.
So we will not discuss my 3.7 or what I've done on a GPS with it.I will say this much, when you guy's meet with GTAFAN he will be able to demonstrate accelleration from 270km/h as he will be running my Ex-3.7 Glenwood Motors stage 4. Are you guy's in for a pleasant supprise.

So Greece is not 'Berks" in the UK. Luckily we have not reached that level of Nanny state.
Monstro

not nanny state but as you say traffic density is likely to be major league difference.

even so it's still a public highway a track seems to be the appropriate place for 200k's plus. don't get me wrong maxxing out a car must be a fantastic and exhillarating experience and fair play to the pair of you for aiming and achieving it however my sypathy would be with whoever you hit on a highway and not either of you.

ok i dont know the Attika highway but if there is the possibility of trucks pulling out on you it seems plain daft. at approx 170mph your covering in the order of 80m/second they've got no chance to see you comming or react in time. blow lambo brakes i'd want a drag car's parachute system fitted. your modifications, applications and desires seem more drag strip orientated or salt flats top speed not track racing or fast GT driving on a road. keep the posts comming however as they make a cracking good read and its interesting to see how far the car can be stretched but it's for very specific purposes and probably unlikley to be taken up by many. however keep us slow coaches updated of your power race.