Properly-Engineerd Braking Systems;

[junglejustice]

OK, so this was one amazing educational process (for me at least) and I am happy to share with whomever else here wants to participate...

As with many other Alfa-folks that I encounter daily, I too come from the school of "...2 sticks of dynamite are better than one!..." It is interesting to see guys (in ALL car circles actually) make the same mistakes and assumptions that I have in the past... It was then quite an eye-opener (for me personally anyway), to go through this education-process with Martin from GiroDisc and see what actually goes in to developing a complete brake solution (one that actually works in more ways than simply just stopping the car over some distance!)

As a side-note, Martin is the guy responsible for the joint-development with Group 2 of their fantastic 4-pot/2-pot bolt-on solution depicted in the attached picture, for the aggressive street/track use of a Milano/75/Alfetta/GTV6 transaxle car. For what they are - a cost-effective (and yes - I use the term lightly when speaking about 3K USD worth of brakes) solution, they are amazing and work extremely well!

When you look at say a bolt-on kit from Brembo (including 8-pot fronts and 4-pot rears) - complete with all brackets, hardware and braided stainless steel lines to adequately stop a 6000 pound 60,000 dollar super-charged Cadillac Escalade SUV for example, you are talking about 8,500 USD. The shop (Group 2) just had a Brabus AMG G55 wagon come through there and the replacement Brabus OEM discs are 1,500 bucks each!

We have all heard about the father and son Enzo co-owners out in the mid-west who ran through a set of carbon fiber discs in one day at the track (at a replacement-cost of something stupid like 15K USD, for just front discs and pads only!)

So for what it is, the complete, brand new, total bolt-on G2/GiroDisc solution for these cars at 3K USD, is mere penance! Sure, we are talking 50% of the total current value of some of our cars (such as say a 6K Milano Verde or a nice GTV6), but who here would actually sell our cars for that? - Especially not after installing 3K worth of brakes...

They are extremely well-balanced, complete and NOT just a bunch of shiny &*%$@ bolted to the car. (Even the most simple minded animals are attracted to shiny objects - just look at crows!) Why are we gullible enough to believe that because 6 pots are more than 4 and 4 pots are more than 2, that they will therefore work better?

Why would we assume that just because they say "Brembo" or "Tar-Ox", or "AP Racing", or "ATE" or "Wilwood" on them, they must be better or even just good for the car? Why would we assume that because they came off of a Porsche, they would be great on our Alfas? Dunno the answers, but let's look at the data behind a properly engineered, total brake-solution, developed specifically for one of these cars in full race-trim...

Much of this starts out as a reverse-engineering exercise of the current system, to try and determine just what the engineers were thinking when they originally designed the system. The total system is then uber-sized with specific attention to the fixed-variables (things that the Mr. Bolt-on will likely not want to/be able to change out in his driveway on a Saturday afternoon such as the pedal box, the brake-master cylinder etc etc.) To compensate for those fixed-variables, adjustments are made elsewhere in the development process to compensate and maintain proper balance in the modified system!

I'll explain later however, for starters - in the attached pictures we can see the collection of components in the current bolt-on solution from Group 2/GiroDisc, (for use with a track/street Milano/GTV6/Alfetta.) Sorry about the finger-prints...

This is a solution that does not require removal/changes to the existing brake-master or pedal setup!

[junglejustice]

Next, some additional brake-shots.

A work-sheet with all of the required variables from which Martin calculates a total-solution for Jes and my two 3.7 litre 24 valve race cars.

And finally, a spread-sheet that calculates the torque required to stop the car with a given negative-g...

(Please click on the links below my pics for the .PDFs - I have no idea how to post the images...

Let the games begin!

[Potenziato]

Nice looking brake parts JJ! I hate you always posting all this Alfa porn on the BB and making me drool!

Seriously, I'm kinda curious that the kit doesn't throw more proportioning to the rear brakes. On the stock suspension this would be a disaster, but with the RS stuff you limit weight transfer to the front. I'm not criticizing I'm just curious. Theory and reality never seem to meet.

[AR4me]

Keep in mind that the 3.7 race cars will have adjustable (from the cockpit) brake bias to suit track and personal style. Though, for a street setup I feel confident that Alfa knew what they were doing. If you want to change the brake balance for a street car you better consider and test carefully. Keep in mind that Alfa has attempted to design the best and safest overall, allround, brake system: rain or shine, snow, dry, ice, summer, winter, etc. You can probably out-do them in terms of optimizing brake bias for one condition and one driver, but for overall perfomance I don't know.
Jes

[junglejustice]

....yes and no... Keep in mind Jes that we are talking about 25 year-old brake technology here for one. We are dealing with more modern materials now and more importantly, the application of those materials; for example varying pad-composition (front to rear), which can play a large roll in front/rear brake-bias (before you ever even touch your in-cabin brake-bias adjustment knob), or make changes to the proportioning valve itself!

As a side-note (and I'll let Andrew Garcia chime in here a bit as he actually has more experience with this particular aspect of it than I do), the older cars such as the earlier GTV6s had better rear brakes - a function of that proportioning valve situated at the rear of the car underneath it to the right! (FYI Jes; on the 3.7s, the "optimal setup" depicted in the design-sheets attached above, calls for us to remove the stock Milano proportioning valves - situated somewhere further up-front on our later cars!)

The GiroDisc design now incorporates best front/rear bias setup right out of the box and the front/rear bias control that we are planning to install becomes more of a fine-tuning tool than it would have to be if you simply slapped it on to a system that was not first subjected to this type of overall planning.

Yes, Alfa Romeo tried to design the best all-around system for all conditions/all drivers - definitely agree with that however, technology has changed much since then and improvements are available (or you and I will be running the stock brakes on the 3.7s Jes...)

Louis, we tend to be very simplistic in our thinking and approach to brakes (kind of the point of my post here...) Most of us look at the basics of what impacts the brakes (i.e. how many pistons front, how many pistons rear, what size discs - period.) You seem to have taken your own thought-process a step further to include the brake-proportioning valve and that's very good.

How about the time that a particular area of disc-surface that has just been impacted by contact with the pad, has to cool down before being exposed to contact with the pad again? That one threw me for a loop!

How about then the commensurate temperature increases in the pad (called the coefficient of friction...), the initial increase in grip and then finally the decrease in performance due to temperatures surpassing the optimal operating-levels for that particular pad-surface area, (as well as it's material composition, the associated disc's material-composition, the sweep-area of that disc surface and again the time that it has to cool and the overall effect just past the peak in that performance-gain bell-curve?)

I know - makes your head spin. And yes, improving the suspension (while not a collaboration between RSRacing and G2/GiroDisc by ANY stretch), does serve to improve the braking! I can tell you that this system - even applied to a stock suspension car maintains great balance and provides huge improvements in the performance of the car!

Did you guys take a look at the Adobe Acrobat .pdf-files attached to the bottom of the pictures in my post above? (I know that Jes saw them when he was here last to pick up the 3.2 GTA Verde...) Its interesting stuff - print them up!

[junglejustice]

...in the design of the stock-replacement aggressive street/track application pictured above, the goal was to come up with a kit that would require the customer to replace as few parts as possible, increase the overall performance as much as possible and keep the cost as low as possible.

Jes, and the others who have driven this setup on the track or on the street will agree that they have arguably achieved those goals!

So, from the pdf-files above; other aspects that come in to play in a design such as this;

Number of pots front; overall diameter of those pistons and total piston-area
Number of pots rear; overall diameter of those pistons and total piston-area
Bore-size and length of the brake master cylinder (or of the cylinder(s) in the case of the all new-designed systems for the 3.7s that will run separate front and rear masters...)
Swept-area of the front discs
Swept-area of the rear discs
Chemical-composition of the front pads
Chemical composition of the rear pads
"Programmed" proportioning of the existing valve(s) (or removal there-off)
Wheel-base of the car
Curb-weight of the car
Weight-distribution of the car
Axle-weight
Center of gravity height
Tire size, diameter etc - front/rear
Rim size - front/rear

They feed all of this in to the spread-sheet and calculate the vehicle's estimated kinetic energy.

Then you move over to the brake-torque sheet and enter a target deceleration-rate in G...

Then there are these two very interesting puppies in the area of fixed variables called pedal-force and pedal-ratio... (It seems that the average driver can only exert 75 to 80 pounds of pressure on the pedal effectively for extended periods of time (effectively - with any kind of feel for modulation) and before another variable called fatigue creeps in! And his companion - pedal-ratio - street cars run a ratio of 3 to 4:1, more serious race cars run 6 to 7:1... The Alfa at 4.5:1 is not half-bad the way that I understand it. (Measured leverage from the pivot-point of the brake-pedal to the back of the master-cylinder...)

And here comes a very good example: In the design of the "bolt-on" street/track setup, the assumption was made that the average owner is not going to want to change out his pedal box, or master cylinder when he/she buys this brake-set, so compensation had to be made somewhere else. Since he/she was probably also not going to be too keen on converting the rear setup to outboard in order to accommodate larger rear discs, some other adjustments/sacrifices were going to have to be made somewhere else in the overall setup!

And so the spread-sheet gradually drives the system engineer down a path of closed doors and fixed-variables until you are left with a hand-full of adjustments at your disposal, in order to improve the braking ad still keep the overall system balanced and working together... What they came up with was the current setup as we know it and see here for 2,995 USD.

[junglejustice]

Finally we start looking at brake-torque and the overall front and rear clamping-force (using this new system) - required to hit that negative-g target-rate of deceleration entered in to our other spread-sheet (and given the weight of the car and driver, given the speed, contact area of the tires and all of the other variables taken in to consideration) - to a point right before lock-up...!

Interestingly enough; in the first iteration of brakes that Jes and I went with for the 3.7s (8 pot front and 4 pot outboard rears) we were not exposed to these levels of planning. While the engineers of those setups took every care to produce a caliper and disc combination that was going to perform well for whatever car they were installed on (and while similar brake-combinations - subjected to smaller caliper combination class-rules - were actually used on the South African Squadra Corse race team 147 GTA cars), who knows what they would have been like on the 3.7 litre Milanos.

Jes' car actually felt pretty good - given what little we drove it before Phoenix took a flight to the car-gods in the sky...

In closing to my rant - funny enough - the resulting calculation for the two monster 3.7s was to be satisfied with simple 4-piston front and 4-piston rear calipers (HUGE ones - of a specified size no less), with 330mm discs at each end and .625 & .7 inch bore masters respectively...

The choice to change the fronts to 6 pots required 6-piston calipers with decidedly smaller total piston-areas per caliper and a change-out to a .7 inch bore front master as well. In return, this also impacted the cost of the front calipers by some 600 bucks to the end-user - all that for just the bragging-rights of 6-pistons versus 4 pistons (while still maintaining the same balanced, complete engineered result of the recommended system specifications...)

With the street/track system right at 3K USD and this full-race version in excess of 4K USD-range (and requiring welding custom brackets to the hubs on the DeDion for the rear outboard conversion), how many buyers will be happy with "just" 4-pots front and rear...? (..."but surely Sir, 8 pots would be better than 4 pots and for the money I can buy 8-piston calipers from XYZ off of _________ Porsche...!"

This is where the "marketing" department and the "engineering" department will have a diversion of opinions (the average buyer looks at the amount of pistons in the caliper - not the design-work behind it.) All because as a consumer, we are not always exposed to this level of detail when buying this type of product.

[AR4me]

JJ,
I think you misunderstood me. I was not saying that the brake bias proportioning valve was not to be touched, I was saying (or, intended to say) that the OVERALL brake balance/bias designed into the cars by AR is probabaly heavily optimized/tuned for optimal overall performance.
Jes

[junglejustice]

...correct-correct.... We're on the same page honey! (It was 2-3AM when I wrote all of that - could not be too attentive to every detail...)

[dretceterini]

The idea of more pistons per caliper is better is, IMO, like saying mine is bigger than yours.

1) The fewer pistons per caliper, the easier (and cheaper) to maintain.
2) Overall performance is what matters, not the ultimate performance potential....especially relative to cost.
3) Why spend 3 times as much money for 2% more perfomance...unless of course you are building a DTM or ETCC type car...

[Barryh]

John,I dont usually get involved in your posts,but the std. little valve under the rear is not a proportioniong valve.
It is actually a pressure limiting valve,ie:it will maintain the same pressure front and rear until it reaches a specified limit .At this limit it will not raise the pressure through added pedal effort,but maintain the pressure as set by the spring to the rear.

A proportioning valve ,depending on setting,will sart off with 2 distinct differing pressures to the front and the rear.This will be maintained throughout the braking action..

So,limiting valve~equal pressure front and rear up to a piont for the rears only..
Proportioning valve~differing pressures from the beginning of the braking process...
Hope I did not screw with your thread.

[junglejustice]

Quote:

Originally Posted by dretceterini The idea of more pistons per caliper is better is, IMO, like saying mine is bigger than yours.

[junglejustice]

Quote:

Originally Posted by Barryh ...the std. little valve under the rear is not a proportioniong valve. It is actually a pressure limiting valve,ie:it will maintain the same pressure front and rear until it reaches a specified limit .At this limit it will not raise the pressure through added pedal effort,but maintain the pressure as set by the spring to the rear. A proportioning valve ,depending on setting,will sart off with 2 distinct differing pressures to the front and the rear.This will be maintained throughout the braking action.. So,limiting valve~equal pressure front and rear up to a piont for the rears only.. Proportioning valve~differing pressures from the beginning of the braking process... Hope I did not screw with your thread.

[nikosd]

Nice work from Group2/Girodisk !

The problem is the price, which is really off the roof ! Even Tarox (similar solution with 6-pot) is cheaper. If you have some time, you can make such a kit for your 75 with less than 1.000 euro with brand new brembo/wilwood 4-pots and floating disks. Just done such a kit at that price in Europe. Could go even lower. A proportioning valve is not difficult or expensive to fit and gives you a lot of possibilities for setup. I understand Group 2 has done a lot of work on their kit (it's obvious), but the price really needs revising instead of advertising in my opinion

Nik

[Barryh]

John,The difference is as in the rough diagrams..
An adjustable proportioning valve will just have differing pressure rises for the rear.Diagram shows a fixed rise..