[SexyLex]

I just purchased a set of BAer +2 Rear Rotors (2-piece) for the Z and someone told me this:

I hope that the fronts are +2 as well... otherwise the ABS is going to be working overtime and the car would be very unstable braking for corners.

I would definitely say that +2 with the stock calipers is for looks only. I can see that the increased torque arm of a +1 on stock calipers is a fair upgrade, but if you are going +2 you probably need more pad area. Those brakes are just going to overheat and fade during track use.

Is this gonna be an issue for daily driving?

I dont intend to track the car but if I do, I'll swap the rotors w/ factory/NAPA ones.

 

[Blue Angel]

ABS will be working overtime during hard braking for sure... with a larger rotor diameter the rear brakes will be generating alot more braking force. Maybe a proportioning valve could correct this?

I don't know what the heck that guy means saying you'll need more pad area to stop overheating/fading during track use??? Fact is the car will not be balanced under braking.

The only way that those larger rear rotors would help is if Chevy had seriously under-utilized the rear brakes the way they are set up from the factory, but I seriously doubt it looking at the phenominal braking performance the 'Vette is capable of. I'd be sticking with stock sized rotors, fer sure!

 

[DJWorm]

It will NOT effect the braking. There will NOT be any problem with the ABS. A brake proportioning valve is NOT needed. A different brake balance spring is NOT needed.

The reason is that the Z06 has an automatic electronic brake proportioning valve and system that automatically checks and changes the brake proportioning about 60 times a second. It will adjust for any changes in the system.

The only caveat is that if you install larger calipers that includes a larger caliper piston surface area then you may have to install a larger master cylinder when you reach a certain limit.

 

[RalphP]

It will NOT effect the braking. There wil NOT be any problem with the ABS. A brake proportioning valve is NOT needed. A different brake balance spring is NOT needed.

The reason is that the Z06 has an automatic electronic brake proportioning valve and system that automatically checks and changes the brake proportioning about 60 times a second. It will adjust for any changes in the system.

The only caveat is that if you install larger calipers that includes a larger caliper piston sutface area then you may have to install a larger master cylinder when you reach a certain limit.

I would like to understand how this system works. Unless it monitors ABS activation (won't happen in normal driving) then how would the automatic proportioning system gather the necessary data to make proportioning changes? In other words, how would it know that the rear brakes are applying increased stopping torque due to the larger moment arm caused by the re-positioning of the rear calipers? - unless they start locking up.

BTW: I passed on the supersized rears since they are $$$ and they weigh more :NoNo: and I wanted to stay consistent with design for performance only. Having said that - I'm sure they look cool!

 

[DJWorm]

The automatic brake proportioning system is independant of the ABS system and has nothing to do with it. It uses different inputs from/on the universal communication bus such as wheel speed sensors, wheel position sensors, steering position sensor, brake solenoid activation, individual brake line pressure, master cylinder pressure, brake pedal position, output data from the ABS and its sensors, etc. etc.

The automatic brake proportioning system first debuted on the '01 Z06 as did the Universal Communication Bus Architecture Format. The individual computers do not have their own dedicated sensors but rather; the UCBAF allows each individual computer on the Corvette to use any and/or all sensor data it selects off the Bus. All the sensors feed coded data into the Universal Communications Bus and each computer selects the data it needs from the communication buffet.

It is so good that many racers have found that they do not need to install a manual brake proportioning system if retaining the OEM brake system and if they do the system is actually downgraded.

The only downside in the OEM brake system as it is used in racing is the dreaded "Ice Mode" program in the ABS system.

 

[RalphP]

Thanks, but I still don't see how any of the sensors you mention would respond to a change in rotor diameter/caliper moment arm. Not disagreeing with you, just curious as to how it would accomplish this.

 

[DJWorm]

The automatic brake proportioning system is also independant of the Traction Control and Active Handling, so it works when they are OFF, but uses many of the same sensors. It has algoythyms of expected wheels speed reaction when the brakes are applied. It monitors the wheel speed and brake system 60 times per second and makes adjustments to the brake solenoids and brake pressure to each wheel.

Thus if it would see a wheel slowing down due to some kind of increased braking force as compared to the others, wether it be an increased caliper moment arm or change of traction due to a pavement change or condition it will adjust that wheels braking power and proportion the other wheels brakes to it.....60 TIMES A SECOND!!

You could probably put four different rotors and calipers and pads on four different size wheels with four different tires and the car could still be driven and stopped ...although not optimally.

Evidence of the automatic brake proportioning working so well, is when larger rotors and brakes are added to the front, such as 14" Wilwood's with 6 piston calipers, and the OEM's are retained in the rear. The proportioning system sees that and increases the rear proportioning to balance the car and the rear OEM pads wear out sooner. But the car stops sooner in a shorter distance but remains balanced. Likewise putting larger brakes on the rear will be sensed, and the proportioning system will balance the car.

 

[SexyLex]

Wow, very interesting & informative.

Thanks!!!

 

[RalphP]

Thanks: So it must rely on the wheel rotation sensors to measure small variations in wheel rotation speed. If the back brakes are too heavily biased, then they must "scrub" before they completely lock up and the rotation sensors can detect a small speed difference and compensate. 60hz isn't really much bandwidth in my world, but it must be enough to do the job. I don't know the exact diameter of our rear tires, but at 60 mph I figure they are doing about 13 revolutions per second so the system gets about 4 samples per wheel revolution.

 

[DJWorm]

Your assumptions are almost correct:

At 60 MPH your traveling 1 mile/min or 5,280 Ft/min

OR 5,280 Ft/min//60 sec/min = 88 Ft/sec

OR 88 Ft/sec X 12 IN/Ft = 1,056 IN/sec

OEM rears are 26.6 in dia
OEM fronts and Hoosiers & Kuhmos are 25.5 in dia.

Therefore:
OEM rears have a circmfrence ( 2PiR Or DPi) = 83.56 In
OEM Fr/Hoosier/Kuhmo = 80.11 In

OEM Rears = 1,056 In/sec//83.56 In/Rev = 12.63 Rev/sec
FR/H/K = 1,056 In/sec//80.11 In/Rev = 13.11 Rev/sec

60/12.63 = 4.75 samples /Revolution
60/13.11 = 4.58 samples /Revolution

Although you downplay the 60 Hz sampling. The processing and communication is much faster (probably 1-2 GHz) because it is also making corrections and revising Brake proportioning at 60 Hz.

Therefore it is changing and adjusting the Brake Proportioning Bias & Balance almost 5 times every revolution of the wheel at 60 MPH. That's an adjustment in less than a quarter revolution or about every 75 degrees of revolution.

At Watkins Glen (long course) for example that means the Brake Proportioning Bias and Balance is sampled, corrected, revised and adjusted:

4.75 samp./Rev X 12.63 Rev/sec X 60 sec/min X 1 mile/min X 3.54 mi/Lap = 12,742.41 Sample Times/Lap !!

Let's assume you would only be braking 1/3 of the time, and that's only when an adjustment would be necessary. That's still:

4,247.47 Adjustments/Lap !!!!!

I would be very lucky as a driver if I could make 1 brake proportioning adjustment per lap using a manual system.

 

[RalphP]

Great explanation - thanks. So, given the Nyquist rate for sampling of 2 samples per revolution, at 60 mph the system can make effective corrections after only one wheel revolution. 120 mph would be about the limit and at higher speeds, corrections would take place over more than one revolution of the wheel. Not bad.

I guess this means that we can also get on our brakes harder in corners before the car becomes unstable or a wheel starts locking up. Maybe this is part of the reason that I hear the Vettes can beat the Vipers at the track? You can brake later?

 

[DJWorm]

Correct, except for the dreaded "Ice Mode".

 

[ScDFACHE]

I just purchased a set of BAer +2 Rear Rotors (2-piece) for the Z and someone told me this:




Is this gonna be an issue for daily driving?

I dont intend to track the car but if I do, I'll swap the rotors w/ factory/NAPA ones.

Call Hal Baer at Baer Racing. I have their Pro+ brakes on my Z06 and none of what you mentioned has ever been an issue - either potential or actual.

VIPER EATER

 

[TexasRedZ06]

Correct, except for the dreaded "Ice Mode".

Can you confirm that this safety feature in our ABS system is turned off when you are in Comp. mode?? I don't race my Z, but it would be nice to know should I try some track time.

 

[RC45]

Exactly what the symptoms whn this ice mode kicks in?

Rapid pulsing of the brake pedal from ABS activaiton even when accelerating out of a bend and not on the brakes?

I remember in the early days when I drove my car really, really hard through the back woods one day - I came out of a bumpy bend and as I crested a small rise under acceleraiton, the brakes kept engaging in rapid succession... not like when Active Handling kicks in - but more like an insane super-ABS session - it was rather weird and unnerving.

 

[DJWorm]

Ice Mode

Selecting Competition Mode or turning OFF the AH & TC does NOT disable the ABS or the ICE Mode program within the ABS.

Ice Mode is an algorythm in the ABS that looks for sudden and rapid deceleration of one or any or all of the wheels. If it sees a time interval that is too short between application of the brakes and lock up it can assume that you are driving on ice. It will then limit the next brake application to 35% and you will have a high stiff pedal trying to restrict you from applying the brakes too agressively.

This situation can be mimicked on the race track or AutoX course when using very sticky race tires (R or A compound) and very agressively braking and getting into the ABS. If the application to lockup time is too short the ABS will activate the ICE Mode. The problem occurs in the NEXT corner when the driver attepts to apply the brakes and finds the hard stiff pedal. This can be very unsetteling as the ABS and brakes worked perfectly in the previous braking zone and corner. AND there is NO warning that the ICE Mode has been activated and will be limiting the brakes in the NEXT corner. Fortunetly ICE Mode can be overriden by forcing the pedal to the floor but an uninformed driver will be surprised and most likely scared to death and lap times will suffer.

You can either choose to override ICE Mode or avoid it by changing your driving style and avoiding the ABS while braking as much as possible. Note that ICE mode is NOT necessarily activated in ABS but only in ABS when the activation to lockup time is too short.

I have only experienced ICE Mode once, while one of my co-drivers experiences it all the time. Our drivng styles are completely different. He is more agressive, brakes harder and does have quicker lap times.

I do not know if Chevy has modified the algorythm, since we and other racers have complained about it, but it would seem a good thing to eleminate in Comp Mode or with AH & TC OFF.

 

[SexyLex]

DJWorm,

In your honest opinion, do you see any benefit or downside in using these rotors for street driving?

T.Y.

 

[DJWorm]

No, except that you might loose the emergency brake. Do they have an internal drum for the E brake??

And they will not cause any problems with the ABS or Proportioning system as I have outlined above.

 

[Blue Angel]

If the caliper is relocated and acting on a larger disc the car has no idea; there is no CPS (Caliper Position Sensor) in a Corvette, or any car for that matter.

When the car is cruising down the road it has no idea that the caliper has moved and is acting on a larger disc.

Under normal braking (where the tires have FULL traction and no slip angle to the road) the car STILL has no idea that the caliper has moved and is acting on a larger rotor.

Not until one or both of the rear tires start to lock up and slide relative to the road surface will the car realize that a correction has to be made. This is usually accomplished by the ABS system, though you seem pretty sure that there is a computer controlled proportioning valve at work here to reduce line pressure to the rear brake calipers totally independantly of the ABS system.

I am not a Corvette expert, so there may indeed be a proportioning system that is adjusted by the car's computer (or its own?), but I will stand by my comment that the car will need to correct for the larger rear rotors and can only do so once slipping is detected, and that slipping will happen sooner if the brake is applying more braking torque to the wheel than with the stock diameter rotor.

I may not be a Corvette expert but I am an Engineer and, as such, I usually require concrete evidence that something exists. Do you have a schematic of the braking system that shows this proportioning system? A GM part number? Maybe I can learn something about my car here.

Also, no car on the road comes with a 1-2 GHz computer for operating any of it's drivetrain systems. The new 500hp V-10 BMW M5 was applauded in one article I read for having an ECU capable of performing "staggering" levels of computation... over 200 MILLION calculations per second! Wow... the most expensive 5-Series ever comes with a 2.3 MHz processor! What a deal, and what TECHNOLOGY! Where's my credit card...

I also don't see why this computer controlled proportioning system would adjust five times per wheel revolution if the car wasn't braking... if I'm at WOT in third gear headed down the straightaway of a racetrack, why would the braking system be adjusting to or compensating for anything at all? What is there to compensate for?

I'm not trying to be a pain in the A$$ on purpose, I just need more than a bunch of wheel speed calculations to convince me that there's something working on my braking even when I'm not.

 

[DJWorm]

Well I am NOT going to do your homework for you, but I will point you in the right direction.

The fact is that the Automatic Electronic Brake Proportioning System is a Dynamic system as it IS analysing and making adjustments ALL the time whether braking or not. In my analysis example of a lap at Watkins Glen I said that it was possible that the system could sample and make more than 12,000 adjustments per lap but that we would assume that braking would only be 1/3 of the time and that we would assume only +4,000 adjustments per lap. That assumption was incorrect and the real correction rate is actually closer to 12,000 per lap. Here's why:

Even though in a racing condition the AH and TC may be shut OFF, the sensors they use are NOT and the algorithyms they use are still active and inputting both the raw sensor data and the AH & TC data outputs into the Universal Communication Bus. In addition the BCM uses Yaw and Pitch Accelerometers and Stability Control and other data to calculate Side Slip Angle Rate and even calculates Pavement Coefficient of Friction Estimations, continuously. So the Brake Proportioning System is not only seeing its own data, Master Cylinder and Individual Brake Line data and Wheel Speed Sensor data from braking when it is actively braking but is constantly being updated with all this other data and it is making adjustments in anticipation of braking using the other data on the universal communication bus.

In short the brake proportioning system is in fact dynamic and is constantly updating whether braking or not in response to all the other sensor and calculated data on the UCB. It also doesn't need to know where the Caliper is in relation to the rotor or what is torque as applied...as it changes anyways and is variable according to pad material, temperature, brake coefficient of friction, tire grip, etc. It is basically an "Outcomes Based System" and only cares what the final result is and makes final adjustments according to how the car is actually braking. It basically only cares what the braking difference is BETWEEN wheels

In addition the brake and brake proportioning system has been upgraded with Bosch's 5.3 Hydraulic Modulator which is more than just a solenoid and can modulate the fluid pressure in response to the brake proportioning system and ABS. So the system is capable not only electronically but hydralically as well.

Porsche & BMW have been using a similar system since 1998 BTW.

F1 has been using it longer.

Here's a brief synopsis on this site:
http://www.z06vette.com/01.php

If you need more info do an internet search under
"Corvette Brake Proportioning System"