johnny c

IF the brakes went from 100% fine to OMG NOTHING! And then where 100% fine seconds later, then that was a computer trying to kill you. I hate factory ABS systems, And not just because if the ice mode.

ABS,
Factory abs is intended for little old ladies to keep control of the car during a rain storm. Motorsports was never in the ABS meeting at GM. To all of my drivers that bring street cars, I tell them to pull the ABS fuse. It is more headache then solution. The GT-R guys always ignore me but after a few sessions I have miata’s out braking them. Bosch makes the current top level motorsports ABS system. The bosh operates 10 time faster than a OEM abs. it operates so fast there is no sharp change in pressure at the pad. It also works to a %. The Bosh can calculate that at a given moment it will deliver 75% of the supplied line pressure to prevent a wheel locking up. A OEM ABS will detect wheel lock up and goes into a ON-OFF-ON-OFF-ON-OFF-ON-OFF-ON-OFF- program until the wheel slip is gone, or there is no more line pressure. The problem a OEM abs creates is it drastically shortens the life of components. I wouldn’t be surprised if your wheel spinning on the rim was from a factory abs. it also makes your pads life shorter and I have seen brand new (very expensive) rotors crack from it. Imagine getting a rotor up to thermal capacity and then hitting 6x a sec it with iron hammers (pads). for my racers that like the rain put the factory abs on a switch. In the rain the rotors won’t get hot enough to cause trouble.


abs failure photos.

johnny c

Morning Robert.
Before I can get into your question I have a few more questions. When you say ceramic do you mean Carbon ceramic, or parts store ceramics? IF it’s parts store ceramic pads get rid of them. Those are not meant to be on the track and I’m surprised they live 20 min. That would also explain the inconsistent braking characteristics. For pads: a Corvette c5/c6 with new generation 200qutg tires and better I would recommend the PFC 01 compounds. The new generation 200qutg tires are the Dunlop drz, hankook rs-3v2, toyo R1R, BFG rival and rival s.

johnny c

Let’s talk Rotors.

There are allot of different aspects when it comes to a rotor.
What is it made from (Iron, Steel, Aluminum, Carbon ceramic, Carbon Carbon)
Where is it made
Is it 2 piece (hat made from aluminum, Rotor ring made from iron)
if it is 2 piece does it float?

Not wanting to spend all day I’ll try to keep the answer short, and focus on the standard parts store rotor.
Standard rotors that you find on Rockauto, Autozone, and so on come mostly from the peoples republic of China. They are covered and machined with oil, the material to make them is not as pure as it should be, and are never made engineered for racing. allow me to explain.

The machining process for Chinese rotors involves blasting the machining surface and tools with a cooling oil. This it to kelp keep the tooling parts cool, this lowers maintenance costs on machines. Then factory workers will wrap the rotors with an oil impregnated paper. This oil paper is in an attempt to prevent rust during shipping, the paper does its job well. The problem with using so much oil is that, it will impregnate itself into the iron, the oil will come out under braking. Most of the time when you see issues creating and keeping a transfer layer, the oil inside the iron is causing that issue. The impurities in the rotor are kicking the transfer layer off. Racing companies like PFC, Brembo, AP, will cut the rotors "dry". Dry means to machine the parts without any oil. It is more expensive to do this but will increase the rotors ability to obtain and keep a transfer layer. It will also increase performance. Anyone that has experienced a rotor get better, is from the oil is fully cooked out. The problem with that is a rotor should be good when it come out of the box till the last day it’s used.

- this photo is from WP a big brake kit manufacture. They have no idea what they are doing.

Next is what a rotor is made from. Iron is easily one of the best materials used for rotors. Size for size an iron rotor will outperform a carbon ceramic rotor. if you have two 14" rotors one in carbon ceramic and one in iron, the iron one will generate a more consistent and higher TQ output. Not to go too far off track… but that is why you see 15-16" carbon ceramic rotors on oem vehicles. The oem manufacturers need the increased a carbon ceramic rotor’s size to get the increased performance. Carbon ceramics will outlast an iron rotor. ...sorry back on topic, right iron.. Iron is one of the most dense materials in the universe. also how pure the rotor casting is makes a considerable difference in braking performance. rotors that are casted in china are known to have excessive impurities, and are often labeled incorrectly. anyone that has dealt with 304 *Chinese* stainless will know what I’m talking about. these impurities will have a decreased effect on braking performance. I like to find Rotors manufactured and casted in the USA or Canada. the US has a higher standard of casting. again PFC, AP, and brembo all are manufactured in the USA, GB, or Italy.

finally the engineering in the rotors could take year to explain, so I’ll focus on balancing only. When a rotor gets hot it cones, it beds, and it looks like a wave. it's never still. The material is constantly flexing. think about a top fuel dragster tire in slow motion.. it's not 100% the same but it is close. that rotor is constantly trying to keep itself together and not explode. in order to stop a rotor from shaking the wheel all manufacturers will balance them. Top Motorsports brake manufacturers will balance the rotor by cutting the entire outer perimeter of the rotor on a lathe. this ensures that when a rotor is at thermal capacity, there will be no places of excess or minimal material. it makes the rotor stronger, and more resistant to cracking. Part store rotors balance the rotors by finding the heavy spot on the rotor and cutting that off.

what not to do.


In motorsports this is a huge no-no. the hard edges give a place for cracks to start, the material has a thin spot on the rotor, and it means that the material that is spinning is not balanced through the assembly. This thin material can lead to more coning (drag) and it can lead to a cracked rotor.

In conclusion, :P. is high quality rotors a waist? Like tools good quality parts are never a waste. On average a motorsports rotor will outlast a parts store rotor long enough to justify the price. Parts store rotors can work, they also let allot of people down. If it was my money, paying for my track day, I’m putting the parts on my car that will insure that I have a fun weekend. I’m not looking not fight the $30 rotor that costed me $800 of track time. Allot of people might say "they worked fine for me". Truth of the matter is 80% of the motorsports population knows how to build a motor, 10% know how to build a braking system. Remember that when you’re in the pits taking advice from other armatures.

When looking for Rotors, Find something with a curved vein, manufactured in the USA,GB,Italy or australia... if you can.

lefrog

If I'm not mistaken, if you do that on a C5 you will lose the rear proportioning valve. I'd rather run with it, a rotor is cheaper than a flat spotted slick.
For most of us, as long as the ABS works it does a good enough job. There is unfortunately no real affordable solution to upgrade the stock C5 ABS unit.

One thing I noted you didn't cover so far was brake cooling. Would your brake pad choice change depending on how good your brake cooling system is?

johnny c

The corvette proportioning valve should be fixed. The engineers built the torque vectoring system into the drivetrain and not the brakes. Pulling a ABS fuse will simply not allow the abs system to activate.
Sometimes when you crack a rotor it will take the tire with it. It also might take the calipers, the wheel, and if you’re going fast enough you’ll find a wall. At that point it’s all about what kind of cage and harness system you have.

Brake cooling is never a bad idea. Nobody short of a F1 team has ever said “I over cooled my brakes”. Brake ducts will make all the components you have last longer, and it might even prevent brake fluid from vaporizing.

Robert R1

These are the carbon ceramics that came on the c6 z07 package, zr1 and now the c7 zr1.

johnny c

right, sorry I overlooked the z07, Generally a poor release is due to drag in the system. example: a dragging caliper. It could also be a worn hub, that is out of round. most of time when the braking gets worse threw out a session I’ll lean more towards rotors overheating and starting to deform. But! that you have carbon ceramic those dissipate heat so much faster, (and they are floating) I wouldn't think deformation to be the case. Talk me threw a braking event. When does the release get bad? Example: is it in the beginning of the session, or towards the end? When does the abs kick on? Is it kicking on when you drive over an object like rumble strips, or does it kick on in the first 1/3 of the turn. To break down what is going on over the internet I need a slew of information. Most of the time I’m diagnosing the driver as much as I am diagnosing the chassis.

I would first check your hubs. lift the car and grab the wheel at 12 and 6. wiggle and feel for a “thunk”. then grab the wheel at 4 -n- 10. Do the same, feel for a “thunk”. If you feel it on one wheel then it’s the hub and should be replaced. I like the SFK hubs. They are expensive but are tough and will last. if the hubs check out OK, next I would check the calipers. with iron rotors in the pits, I would just run around with a probe and see if there was a spike in temperature. With carbon ceramic rotors that is not possible, they cool off too quickly. We’ll need to stick temperature tape to the calipers. What you’re looking for is one caliper to be significantly higher than the rest.

96CollectorSport

The 01 - 08 Corvettes with Delphi ABS will shift almost all of the brake bias to the front of the car if you pull the ABS fuse - at least that's the way it feels. They have "dynamic rear proportioning" so the ETBCM / ABS valve body controls the brake bias. So pulling the ABS fuse really messes these cars up bias wise. We've tried running with the fuse pulled and it's a nightmare.

johnny c

ugh that makes life very difficult. we'll need to build systems on paper first. Trial an error will almost be completely eliminated because the system will be constantly changing the bias. there must be a way to send it fixed signal so it won't move.

ErnieN85

The 09 & up use a Bosch system I haven't tried to pull the fuse on mine.
I'm pretty sure it has dynamic rear proportioning also
mine is 75% street car so a full race setup is out

johnny c

the bosh system is out for 99% of people. it costs $10k to buy, then you need to rent a bosh engineer (fly one in from Germany) to set it up, oh and he won't show up to a track day, you'll need to rent the track for the day. then he will only fill 2 of the 18 channels.

so we'll just need to work around it. we'll just need to treat ABS engaging as a serious issue that it is.

Robert R1

The slow release/binding happens in long braking zones where you're scrubbing off a lot of speed. Turn 7 and 11 at Sonoma/Sears. Turns 10 and 14 at Thunderhill are the biggest offenders.

The abs happens when applying the brakes in the 100-120+mph range and slowing down from there. Thunderhill T1 is a great example. The car is at 140-143mph range and slowing down to about mid 90's. ABS will kick in pretty much most of the time. It does happen in the first 1/3 of braking but once it kicks in, it's hard to dial it out (if that makes sense).

However, braking from slower speeds and I can slam on the brakes (I'm generally progressive. the slam was just an example) and the ABS never kicks in. Example would be turn 4 at Sonoma. Coming down 3A in the high 80 mph range and slowing down to high 40's, the car just halts and brakes smoothly.

If there is something in my driving I need to adapt to play nice with these brakes, I'd be happy to! Let me know if I can provide additional details.

zigspeed10

What brake pad compounds are used in professional motorsports? I'm curious if the commonly available pads that we use are the same ones the pros use.

What factors determine the choice of rotor size? Is it just the thermal capacity requirements where once you have that met anything larger is just extra weight or are there other advantages to larger rotors?

johnny c

good news is I don't think it's you.
Do you have any brake cooling? If not you might want to add it. if so, you might want to increase it. It sounds like there is a significant amount of drag in that system. I would apply temp stickers to the calipers to see if you can isolate what side is dragging. If the temp stickers show nothing then it’s just how the system was engineered.

Temp stickers. [IMG]

[IMG\]

With high speed abs it sounds like the car is lifting. It has been documented that the C6 ZRI chassis will have 85lbs of lift (F) and 30lbs of lift in the rear @ 140mph. A cheating way to gain some front downforce is to lower the nose. I would also look into a splitter, and maybe a small spoiler.

Everything I have listed here are educated guesses and should be tested.

jtmck

Let me see if I understand this.
In the 01-08, there is something in the ABS box that when activated allows the rear brakes to work and if you pull the fuse it mechanically shuts off the rear brakes?

I have a 1998 and I thought that pulling the fuse simply, by default, gave you regular braking.

Am I wrong here?

Really good discussion on brakes.....

johnny c

Brake compounds used by pros today are Padgid (made in Germany) , PFC (USA) and Project Mu (Japan).
everything else is just playing catch up.


There are 3 ways and only 3 ways to Change braking tq in a system. Rotor Size, Pad compound, and Hydraulic advantage.

Rotor size,
Increasing rotor size is the best way to increase Tq in a system with minimal handicaps. You can put a very large rotor on to a car and this will increase tq with a very minimal effect on modulation. Iron rotors are heavy. That needs to be kept in mind also a larger rotor needs a larger wheel, also heavy. Rotational mass is 4x as important as unsprung weight. So if you can shave 15lbs off a corner (multiply by 4 corners) -60lbs in rotational mass, 60x4 =240. Your car will behave like you kicked your fat brother out of the car.

Pad compound,
Discussed dealer in pads the pads Torque is another way to change overall tq in a system.

Hydraulic advantage.
Give me a lever and a place to stand and I will move the earth- Archimedes 225BC. A hydraulic system is just a liquid version of a lever. The master cylinder is smaller than the caliper’s pistons. This creates a ratio to magnify pressure that is compensating distance. For example the mc will move .5”, the caliper’s piston will move .05” the pressure applied will be 100lbs, the pressure at the caliper will be 1000lbs. we can manipulate that pressure to our advantage to get a higher or lower line pressure all while compensating distance traveled. Great you think to yourself, I’ll just make the pedal move 50” and I can get rid of my booster. That’s not the best. A pedal moves on an arc. Once that arc travels past 90* to your hips your body loses efficiency. So that distance does need to be taken into consideration.

To circle back and answer your question how to size a rotor. When I’m picking out rotors I look to the opposite axle. Balance is key, remember the story I told about crashing in autocross in the pad section. That balance is THE MOST important part in the entire system. I don’t want to see a 355mm rotor with a 275mm rear rotor. That car will have a hard time slowing down. The other things I take into consideration it where the weight in the chassis is. A rear engine car will have a larger rear rotor then a front engine car. A larger rotor will live longer. On my track day guys I try to shove a huge rotor and endurance pads under a car. It might cost a few hundred bucks more, but the longevity will pay it back.

Bill Dearborn

No. The 01-13 C5s and C6s had dynamic rear proportioning. That means the ABS controller controls how much brake bias is applied by reducing the pressure at the rear wheels. If the EBCM fails there is no control and no proportioning other than the difference between front and rear piston areas and rotor diameters. Theoretically, when the ABS goes by by you should get maximum brake pressure in the rear (ABS reduces brake pressure and can't do that when it isn't working). That is generally too much and you get the situation where the rear wheels are locking up too soon. The 97-00 cars had a mechanical proportioning valve at the output of the master cylinder. DRM used to sell a spring kit for that valve which increased rear brake pressure thus shifting brake bias to the rear.

The advantage of dynamic proportioning is it eliminates a component and replaces it with code. Also the more grip you can get in the rear the system will detect a reduction in wheel slip and allow more brake pressure to be applied in the rear.

Bill

johnny c

we hope. on most street cars the prop valve is set up to kill as much rear fluid pressure as it can. that way when grandma slams on the brakes it just locks the front tires, and doesn't send her spinning off into the trees.

Bill Dearborn

With DRP the valve isn't required which cuts a part out of the bill of materials, saves a few pennies per car. If you do that across a few million vehicles it adds up to some serious money. In GM's case that adds up to about $1.5M per year that goes toward the bottom line. Eliminate a few other parts by replacing them with code and you can get even more profit.

Bill

Robert R1

I have stock cooling and my Z07 and it doesn't have the aero package so I only have the small chin spoiler as the regular Z06's. However the owner before put a ZR1 rear spoiler on the rear which is likely creating even more lift. I'm always fighting understeer in the car also.

The cooling is stock also. I'll look into getting the ZR1 front splitter and add some cooling ducts to the car to see if it helps. Seem like a good plan? Since I have the mag shocks, I'd prefer not to mess with the rake of the car. It's at stock height.

I will get the stickers as the above don't address the binding issue. Thank you!