Does anyone have any braking questions.
 

Johnny C is the majority of my real name. I'm a "brake guy" by profession and by hobby. I have an obnoxious amount of brake tech swirling around my noodle. If I crammed that info into a Book, nobody would read it. It's some of the driest information anyone could imagine. If and only if you have an issue with your brakes would you pay attention. I find the best way to educate the public is by starting a discussion.

About me: I'm a former PFC factory Rep. I've worked with top racing teams like Joe gibbs racing, Ganassi, Rum bum, Irish mikes, so on, and so on. I've been in the motorsports world professionally starting in 2006. I've worked hand and had with teams and engineers to build braking systems and to fix issues with braking systems.

If you having an issue with your brakes, please ask. Or if you are looking to upgrade your brakes, please first ask. The majority of club racing related braking issues I come across, are from individuals who tried to upgrade their system without an understanding of how a system works.


Disclaimer: I am not a sponsor, so I will not be offering anything for sale. I am doing this solely for the education of the community, a way for me to give back.


Cliffnotes:

[QUOTE=Johnny C @ OG;1589997012]Johnny C is the majority of my real name. I'm a "brake guy" by profession and by hobby. I have an obnoxious amount of brake tech swirling around my noodle. If I crammed that info into a Book, nobody would read it. It's some of the driest information anyone could imagine. If and only if you have an issue with your brakes would you pay attention. I find the best way to educate the public is by starting a discussion.

About me: I'm a former PFC factory Rep. I've worked with top racing teams like Joe gibbs racing, Ganassi, Rum bum, Irish mikes, so on, and so on. I've been in the motorsports world professionally starting in 2006. I've worked hand and had with teams and engineers to build braking systems and to fix issues with braking systems.

If you having an issue with your brakes, please ask. Or if you are looking to upgrade your brakes, please first ask. The majority of club racing related braking issues I come across, are from individuals who tried to upgrade their system without an understanding of how a system works.


Disclaimer: I am not a sponsor, so I will not be offering anything for sale. I am doing this solely for the education of the community, a way for me to give back.[/QUOTE
Lots of brake stuff going on here :D
Do you work at OG?
If so any Wilwood pads in stock (6617) or (7416)
I have not seen them on the OG site

I do. but again i'm not looking to sell stuff as current sponsors will get mad. i'm just trying to give back to the community.

I've seen a lot of brake topics with bad information. lots of guessing involved and limited testing. I also see a lot of "It works for me". I seriously get royally mad at "it works for me" solutions. when i see that quote it tells me is that " I don't know what i'm doing, so i took a stab in the dark, and i'm not dead so it must be fine."

When comparing various pads it's almost impossible to find anyone "in the know" who will share mu data from a brake dyno. If someone is looking for the pad with the most "bite" how do you choose?
I understand that there is more to a set of pads than just bite, but it would be nice if someone would share some info for comparisons sake.

Johnny,


I have a GS with stock brakes.... Looking for a rotor/pad combo that's 70% street 30% track/AX. Took me 5 sessions at COTA over the weekend to warp the stock stuff.


What would you recommend if you didn't want to break the bank? Seen varying opinions on the topic.


Thanks in advance.


Chris

Your right. Anyone that knows about brakes won’t say peak Mu (coefficient of friction). I know what peak Mu is of regular used pad compounds I also know how and where to apply what system. You see if we let that information get out everyone will just want the pad with the most Mu. Pad Mu is not equal to horsepower. More is not better, more Mu is a lot worse. A little back ground story in 2004 digital cameras where just becoming main stream. The mega pixel race was on. 2mega pixel was better than 1. 4 was even better because the images where larger. Once the megapixels got past 7 there was no real benefit to a daily consumer. Hell, you can print a billboard with 5 mega pixels. The camera marketing people kept jacking the pixle count up to 10-15 hell I’ve even saw 20 mega pixel. All the while the consumers didn’t know what they were buying. They went mad with gimmie gimmie gimmie pixel count. We don’t want the same thing with brake pads. If you have a system with too much Mu it can become dangerous. Companies that are brand new will post Mu in hope that people will buy it without knowing what they are getting, just to make a sale. The companies that have been making pads for the last 30 years know to keep Mu chatter down and recommend the right pad. Pads brake down into 3 main dynamics (listed in chronological order): Bite, Tq (Mu) (coefficient of friction) , and modulation.

More to follow….

Bite.
The majority of people think a high bite is good. Again Brakes are not the same as horse power, More is NOT better. We are trying to build a balanced system, not a monster. I’ve heard the Wilwood rep at events talk about “huge bite”. I have beef with wildwood FYI. Another time for that story. High bite does have its place but road racing is not it, allow me to explain. Bite will be reflected as a spike on a dyno graph. It’s the characteristic of the pad when it first comes in contact with a rotor. The pad compound and rotor slot profile will affect the pads Bite. Generally manufactures have their own bite characteristics. So a hawk dtc-60 will have a similar bite as a dtc-70, same goes for PFC and for Padgid. When picking out pads you want to find a pad with soft bite. “Why?” you might ask, and I will tell you. This initial application of the brakes is the only time you can be vigorous on the pedal. If you have a pad with softer bite you can really jump on the brakes. It will help keep the tires cohesion with the track. A higher bite pad will have a greater tendency to lock up a tire and flat spot it, flat spots cost money. The pads that have soft bite are the higher priced pads the pro’s use. Brands like PFC, Padgid, and Project Mu. Brands that have a very high initial bite I recommend for drifters. These are the people that want to very easily lock up a system. Brands for them are wildwood and hawk.


Mu, Torque, coefficient of friction.- all the same thing.
Tq of the pad happens during the deceleration process. This is the time while the brake is applied. Tq is the pads bread and butter. This is where people like to get themselves in trouble. Remember this isn’t horsepower, more is not better, and less won’t make the car easier to drive. When I give classes I start out with a question, I ask “what stops the car”. 90% of the time People shout out “the brakes”, I say “WRONG!! the tires stop the car”. It’s a cheap move, but it quickly gets my point across. For picking out a pad we want to match the TQ/Mu levels to the tire being used. The big mistakes I see are, using too much TQ FOR THE TIRE, too little TQ FOR THE TIRE (see a trend?), not balance the system. The PFC 05 compound is a ultra-high torque race pad. Example: on a corvette with the 05 compound matched with a set of BFG rivals or Hankook RS3 they would smoke the tires regularly. That car would also lose all Modulation (covered later). The pedal would turn into a light switch (off/on). This is the main reason Mu numbers are not published. Brake manufactures don’t want you running out buying the top shelf, and having a chassis that can’t take it. For those pads I would want to see a good amount of downforce, a big +285mm slick tire before I could recommend them. On the opposite side of the coin too little tq. I see this a lot with track noobs, and people that are a bit timid. The noobs sometimes just don’t know any better and just run street pads. The people that are timid think that a lower tq pad is better for someone who is learning. Low Tq pads that get overpowered by the tire can very quickly melt an entire braking system. Low Tq pads have a tendency to leach heat into braking components. A lot of time when I have customers that are boiling their fluid, they will have a pad that has too low of tq. Again we need to match the pad to the chassis. Generally padgid yellows and PFC 01 is a good combination for a normal track driven corvette.
The final issue I see is balance. The single most important thing you can to increase braking performance is to balance your system. An example story. I had ordered a bbk for my car. All big brake kits come with crap $2 pads. unknowing I took those pads to a track day and proceeded to smoke the hell out of them. I had an autocross the next weekend so I ordered up a set of HP+ for the front only. Took them out and beaded them on the street, everything felt fine. A reminder that I had cooked Chinese pads in the rear of the car. I line up at the autocross for the start, I charge down a good size straightaway, I reach for the brakes and got nothing but smoke. I locked the front tires and proceeded to fly off the track and into a berm. What happed is I increased the Tq of my front brakes somewhere in the 100% range, but the rears where completely lacking. I increased the TQ but decreased the overall performance of my chassis. When buying race pads don’t forget about the rears, they are 50% of your system.

Modulation
You will feel modulation when you lift off the pedal, it’s the release characteristic. This characteristic is the most noticeable. It’s also the most dependent on the chassis! Another short story. In 2010 I was racing in the 24hours of lemons. We had a ford escort with 205 (tiny) falken 615k. the owner called up Porterfield and just ordered the most expensive pads they had for that car. Going into turn 1 the brakes where strong, very strong but all the time I made in brakes, I lost when I couldn’t keep up the momentum. Entering the turn the modulation was a light switch it went from 100% on to 100% OFF. Forget about trail braking, that would be impossible. What effects modulation? The pads will have their own characteristic, generally an over tq pad will kill modulation. So it’s very important to have the correct compound.



hold for updates

Ok, here are a couple of problems that have been baffling me for a year. I have a C6Z with Wilwood W6A calipers in front and W4A calipers in the rear. I have their 14 in G37 material 72 Vane rotors at each corner. On track I have been using the Wilwood A compound in the front and the H compound in the rear.

My two issues are:

I am getting spinning of the tires on the rear rims under braking. This has occurred with two different sets and sizes of rims. One setup was with aftermarket Z06 repro 18x12 wheels with GTI Compound Continental Slicks mounted and the other was with CCW 18x13 wheels with Hoosier A6s mounted. There is less spinning of the tires on the CCWs but there is still some.

My second issue is a sometimes the car doesn't slow well from high speeds. This happened 3 times over two events last year. This year I was backing out of the throttle before the braking point and pumping the brake pedal to try and ensure I didn't get the same problem again. For example last year with the Conti Slicks I came into T1 at VIR at speeds close to 150 mph and the brakes worked fine. Two laps later I came into the same turn closer to 140 and when I hit the brake I got a hard brake pedal but not much stopping power. My rider and I went off the end of the track at about 90 and the first thing he said to me after we came to a stop was why didn't you hit the brakes?

Have I chosen the wrong compound? Does the tire slippage on the rear wheels have anything to do with my intermittent no stop situation? Am I getting into what the autocrossers call Ice Mode?

Bill

You mentioned pfc. They used to offer a really nice two piece caliper front brake setup for corvettes to comply with grand am rules. How come they no longer offer that?
The kit they do offer is a monoblock. Why on earth do they insist on powdercoating those calipers where as all the race level calipers are nickel plated?

Like I s said previous I can’t recommend anything. Due to non-sponsorship. I can say this. Street pads are built to do one thing, Be quiet. Squeaks are 92% of warranty work that oem’s do on brakes. Any street pad that is built the main focus is on how quiet it is, everything else is secondary. Also Street pads to maintain a level of quietness use fillers to dampen vibrations. I have no clue what thee fillers are but they are flammable. Being at the track as often as I am, I do see brake fires more then I should.

Race pads, in order to be stable at elevated temperatures ALL race pads have a high iron content. That Iron turns into dust, that dust gets on your wheels, and when it gets wet it will rust. If you like your wheels it is imperative you clean that dust off after an event.

You’re talking about running at cota, you’re going to need real race pads. I have yet to see any pad that can do double duty that can take high temperatures and not kill a set of wheels. Yes I have tested Hawk Street/Race pads, and Carbotech bobcats.

I’m sure that Kit is still available somewhere, lost in some obscure part# book deep in the bowls of PFC. But the Mono-block kit is better let me dive into that below. I don’t think c6’s are legal for Grand am anymore.
They don’t sell nickel coating for street kits because it’s royally expensive to get them coated AND road salt will tear up nickel coating. The Powder coating is less expensive and a lot more hardy, the red can turn gray with extreme track use, get the yellow ;).


Calipers are only as good as how strong they are. There are plenty of other features that go into but the stronger the caliper is the better it will perform. Caliper flex Is a huge issue… and screw it I’ll also cover Pistons.

Caliper Flex,
This is when the brake caliper thinks it’s a butterfly. All different manufactures this happens at different times. I have a 350Z track edition with 4 piston brembos. I could modulate the pedal at a stop and hear the caliper flexing on the pad’s backing plate. The most evident clue that you have a flexing caliper is pad taper. You’ll see that the pads are not worn evenly. “so what” you might ask yourself A Caliper that creates a pad taper is a caliper that flexes, that flex will create drag. 370z sport brakes are notorious for doing this. the 370-sport brakes are complete garbage and they heat up brake fluid very quickly. People that Don't know braking systems like to blame the fluid, as that is the component that failed. When in actuality it's the caliper storing the heat like an oven and inserting it into the fluid. some people might remember the 370 that a journalist drove into a wall during the z's release. I think the journalist blamed the brake pads. shows you how much an auto journalists know about brakes. Anyway I digress... A flexy caliper. A 2 piece caliper is only as strong as the bolts holding it together a mono block caliper is much stronger as it much more contact points threw out the caliper body.

PISTONS. omg pistons drive me mad. I get asked all the time "should replace my piston with stainless pistons"... STOP!! the pistons need to be made out of the same material as the caliper is made from. I have no idea who invented the stainless piston but that guy needs to kicked in the balls. I've had to fight this topic for a while. If your caliper expands at a different rate than your piston then you have a higher chance for those pistons get locked in the bore. this is especially true if you're near the end of pad life and the pistons are really hanging out. the excessive tolerance causes caliper failure and leaks. yes stainless does transfer heat less than aluminum but replacing the piston with stainless is not a good idea. Instead, if you are having heat issues try an insulator. plenty of circle track shops carry insulators.

Read this if you read nothing else.
And one more thing about PISTONS. The Amount of pistons you have means almost nothing to performance, in fact having more pistons than 4 the performance gets worse. I was having lunch with a brembo engineer. We were discussing having trouble fluid pressure consistent across all 6 pistons, and when they stepped up to 8 pistons the problem magnified. The perfect amount of pistons to have is 4. Anything more than that you’ll start to have problems keeping the fluid in the pistons consistent. If the piston area is equal between a given 4 piston and 6 piston the 4 piston will be more consistent. They only time we stepped up to a 6 piston was for space restraints. That was mostly in the nascar cup cars. They had 15” wheels and we were trying to fit a 13” rotor ergo we had to use a 6 piston to get the piston area. ALL of my SCCA GTA cars run 4 pistons. The scca kick down points for people running 6 pistons. It’s a stupid rule that gives an advantage to people that know how to build a system.

Afternoon bill,
The tires spinning on the rim is a tire/wheel issue. I would consult a contental engineer. If you go to an imsa race their engineers are all over the place. That would be an excellent time to pick their brain. My only guess would be that your using your factory ABS. Factory abs units work 10x slower than a bosh motorsports ABS. and the factory abs will punish all the components. Most of the time we see cracked rotors as a result of a rotor at thermal capacity and then playing patty-cakes on it.

Let me ask a few more questions about your flying off the track. Where you getting any warning signs? Example: Was the pedal feeling funny before this? After the incident did your brakes come back, if so.. how quickly?

I have a question. I have a C5 Z and I currently have a AP T1 12.8" kit along with the stock rears. Should I go to a 355mm system in the front, do I need to upgrade the rears too? The rears are so small on a C5 Z but I often hear things like weight transfer, the rears don't do much, etc.

I feel like if you upgrade the fronts you should upgrade the rears too. Otherwise I just feel like you're unbalancing the system even more. I didn't do this with my AP kit but it's the same size as the original C5 setup.

What are your thoughts on this? Do you feel like you can just have a large kit in the front or would you get even better braking with a balanced setup such as ST60/ST40?

When I’m balancing a braking system I’m looking at the cross weight. Corvettes have a very good tendency to be 50/50 if not better. With cars that are that balanced the rears are doing a hell of a lot. Hell on the rear engine cars we’ll install larger rotors on the back then we will on the front. But to answer your question. If you’re looking at a 355mm kit you will definitely want to upgrade the rears too. Stock rotor size is a 12.7” (323mm). upgrading to a 355 is almost a 10% increase. That’s a lot for the rear components to make up.

That sounds like Ice Mode, Bill. The track crests at the 4 marker in the brake zone for T1. If you apply the brakes there as the track falls away from the car, you can easily meet the conditions that trigger ice mode -- three or four wheels locking up simultaneously. I datalogged an Ice Mode event with my Aim Solo DL, so I can show you what happens to all four wheel speeds. Essentially the car puts all the brake bias rearward and lets the fronts rotate freely for steering on ice. Hard pedal, no ABS events. Algorithm expects the user to pump the brakes, so you really can't release the brakes and make it go away before you go off track. Stay left when exiting the track in T1, there is more run off that way and a sand pit!

Hi Bill,

Try using hairspray next time when mounting your wheels. This has helped with the slippage with my tires, and more recently my Finspeeds have a knurled bead which also keeps the tires from rotating.

Also, I used to experience ice mode frequently with my car as I tended to late brake a lot. But, I have since changed my braking points and habits so to avoid any issues with ice mode.

That's consistent with my experience. I first went with the LG/Wilwood 12.8 kit up front (very similar to the AP) with C5 Z06 stock rear calipers. A year later (just a couple months ago) I added the Wilwood 4 piston kit for the back and it made a very noticeable difference. I get into ABS a lot less, reduced my braking zones, and became more consistent. Also going a lot more weekends between brake jobs.

The brakes didn't give any indication of an issue before or after the off track excursion other than the grass picked up in the front brakes was burning as I drove back onto the pavement. The only reason I say the pedal was hard is because it didn't feel any softer than previous braking efforts.

Yes, I am using the factory ABS. The car is a street/track car VS a dedicated track car. Since the rear tires were spinning with two different sets of wheels and two different sets of tires I was wondering whether that was triggering the ABS since the rear rims/hubs would have stopped turning while the tire kept turning until the ABS released the brake pressure to allow the rim to start turning. If that happened quick enough with alternating rim stoppage and turning maybe the rear brakes weren't contributing their part in slowing the car.

Bill

That is about where I was hitting the brakes. Lifting off the brake isn't the most natural thing to do when coming into that turn. This year I am a little spooked driving into the corner as fast so lift off the throttle to keep the speed below 140. If there are cars ahead of me I try to give myself some cushion so I don't run over somebody just in case it happens again. So far I haven't had a repeat off course.

Bill

Firstly, thank you for sharing your knowledge with us. It's greatly appreciated.

I run a 2011 z06 with the z07 package that has ceramic brakes. Car is stock with poly bushings running Michelin sport cups (now cup 2's). Fluid is Castrol Srf. Car is aligned with -2.8f, -2.0r, 7.8caster, no toe front and 20 total toe in rear. Shims are used to keep the alignment from drifting.

The wear tapered, esp the fronts. My front to rear wear ratio is 3:2 I know come guys say they can do 2:1 or 3:1 but I haven't been able to. Longer runs destory pad life. While the performance of the brakes is ok during long stints, it comes heavily at the expense of pad life. We're taking full tank sessions which is around 19-20 laps.

My biggest issue with the pads is ABS kicking in without any predictability. I can literally do the same thing each lap but it'll go from good smooth braking to abs intervention without any reason. Also the brakes will sometimes continue to feel like they're slow to release even after I'm fully off the pedal. Due to this inconsistent behavior, I've pretty much limited myself to braking in a straight line so I can better control the unpredictability. Your thoughts?

Tire wear doesn't seem to have much of an effect of the condition. The burnishing procedure is done on each pad set.