Z4M Brake Bias and New Pads

[Shipkiller]

Since we had five MC's at the track today, I was able to talk to some really experienced drivers in the MC. I was also able to talk to the driver of the 'DogBones' Z4MC race car, which as some of you know is no more. I can't remember his name right now. For clarity, I'll find out tomorrow.

As we talked, I related that when I get into heavy braking, the rear end gives me a little shimmy which can be a little disconcerting. This issue has always been there and is NOT caused by the splitter.

He (Dogbones driver) said that they had the same issue on the race MC and the reason that this happens is that there is not ENOUGH braking force on the rear wheels.

He recommended to go to a different pad on the rears and that should clear it up.

I run CoolCarbons and not a dedicated track pad.

Now, what I am wondering is can I get a better/more aggressive street/track pad for the rear than what I am using now?

Or just go to a track pad setup for on the track?

Just musing and wondering.

[jmillet]

Originally Posted by Shipkiller

Since we had five MC's at the track today, I was able to talk to some really experienced drivers in the MC. I was also able to talk to the driver of the 'DogBones' Z4MC race car, which as some of you know is no more. I can't remember his name right now. For clarity, I'll find out tomorrow.

As we talked, I related that when I get into heavy braking, the rear end gives me a little shimmy which can be a little disconcerting. This issue has always been there and is NOT caused by the splitter.

He (Dogbones driver) said that they had the same issue on the race MC and the reason that this happens is that there is not ENOUGH braking force on the rear wheels.

He recommended to go to a different pad on the rears and that should clear it up.

I run CoolCarbons and not a dedicated track pad.

Now, what I am wondering is can I get a better/more aggressive street/track pad for the rear than what I am using now?

Or just go to a track pad setup for on the track?

Just musing and wondering.

If you plan on doing more than a couple of HPDS events a season then bite the bullet and install high temperature pads for track driving. There are several good brands on the market and everyone has their favorite. I've gotten great performance and good wear longevity out of the Performance Friction PF-01 pad.
YMMV

[Caddyshk]

Jay - I think its more to do with the balance of the car under heavy braking - mine does it too. Adding more braking force to the rears could be problematic... I actually burnt the rear pads off the car two years ago so I don't personally believe its brake bias...

[johanness]

But if Dogbones recognized the issue in his race-car MC and cleared it up with beefier pads in the rear. . . You'd think it'd be a logical 1st step w not too great a cash outlay

[Caddyshk]

Originally Posted by johanness

But if Dogbones recognized the issue in his race-car MC and cleared it up with beefier pads in the rear. . . You'd think it'd be a logical 1st step w not too great a cash outlay

Have you seen the video where he wrote that car off?

[johanness]

Link?

[Caddyshk]

Hard to find - stills...

[Finnegan]

RE: stills. Yikes! I"m glad he "ran away" from the crash but geez it's amazing he did.

Ship, have you talked to either Turner or Zeckhausen? From what I've read altering the brake bias is a very advanced configuration/set-up. I have no personal experience, but if I were thinking about it I'd give those guys a call and get opinions. The advice sounds like it's worth trying but as for which pads would best achieve that goal those guys may have some ideas/experience.

[Caddyshk]

Originally Posted by Finnegan

RE: stills. Yikes! I"m glad he "ran away" from the crash but geez it's amazing he did.

Ship, have you talked to either Turner or Zeckhausen? From what I've read altering the brake bias is a very advanced configuration/set-up. I have no personal experience, but if I were thinking about it I'd give those guys a call and get opinions. The advice sounds like it's worth trying but as for which pads would best achieve that goal those guys may have some ideas/experience.

X2

[inTgr8r]

+1
playing with the bias is not something I would want to do w/o expert info.

[onelove]

Every car is going to react differently to changes, suspension setup and weight transfer as well as tires are going to effect your braking just as much as a pad swap, so before taking advice based on what racecar x or y uses, need to evaluate the whole setup.

I would definitely invest in a track pad setup first and see if the problem persists.

[Caddyshk]

Its not a "problem". I would argue a benefit because the feedback is telling you you're on the edge...

[onebluemcm]

Lets just get the facts straight. The guy Ship (and MFGJR, and several others) met at the track is team owner, of the former Z4MC Grand Am car. He has driven E36 and I think E46 M3s, among other non BMW cars, and owned the former Z4MC in addition to several 996 P-cars. Also ran and raced a bunch of cobra kit cars and a driving school in that car. Just trying to keep people honest. Anyways, he's got a long history of driving, and then owning teams. Was mentored by Tom Milner of PTG.

This "tail end gets squirrelly" issue is quite the sensation for sure. Regarding the race car, it's hard to make much of a comparo to a street Z4MC. Front brakes were modified to fit in a 17" Forgeline wheel. The front end was a Performance friction set up - caliper and rotor. Rear was a PFC rotor or a stock cross drilled CSL rotor with M-caliper and obviously a different pad.

I think the point being made on Saturday (I was there too, spectating; pure coincidence that Mr. Marcus was there as well - we had different agendas...he happens to be a close friend, I was on crew with the team for two years, yada, yada, yada) is that fiddling with bias is not the way to go on a street car. Getting the rear brakes to bite a bit better, with a fully, normally functioning ABS system taken as a given here, should settle down the car. He made reference to a GT500 Mustang they have been working on for the past month. This car has had easily $50k of suspension and chassis mods done to it. He made reference to the same "squirrelly read end under braking" in the GT500; I'm sure we all know this is a way front end heavy car compared to any BMW chassis, and loads of straight line power too. They had just had this car to VIR the weekend prior to weekend for a shake down after completion of the work. This car had the same thing, and they put a slightly more aggressive rear pad on as compared to the front and it supposedly settled it down. I have no reason to think it didn't work, but I wasn't there.

The main idea: use a slightly more aggressive rear pad for more initial bite, compared to the front, and a change should be noticed. Running a more aggressive pad all around is not the idea - the idea is to have a slight difference in initial bite between the front and rear, regardless of what pads are being run. This is the theory, in practice it's hard to find the right balance of pads - this was an eternal struggle with the Z4MC Grand Am car. Also, though we went through what seemed like every pad combo known to man in the Grand Am car, I'm sure there were other combos that never got tried. It's trial and error and there are many, many combos - just look at how many compound types are available!

To this day I still wonder how much of it is sensation. It's still about the only chassis out there where you sit as far back as you do. Maybe it's just one of those chassis where you have to brake a little harder sooner and make up for it getting on the throttle sooner. The chassis definitely can be made to hook under acceleration out of the turns.... I recall the drivers saying it was a complete hoot to trail brake in....

Originally Posted by Caddyshk

Have you seen the video where he wrote that car off?

No video in existance. The only thing that comes close is a lucky photographer with a high frame rate camera was overlooking the roller coaster and captured it - that's where the You Tube "vid" comes from. I was there, witnessed the wreck, talked with Davis afterward, it sucked more than anyone can imagine because of what the car stood for, on top of the monumental loss of a race car.

[Shipkiller]

Ok,

I am NOT looking to modify the bias of the braking system. Too costly and problematic.....

The most cost effective way to get rid of the 'squirm' would be with a different pad in the rear.

After today on the track, I am not going to do this.... It seems the 'squirm' that I have been feeling over the last couple of HPDE's is now gone.

It does seem that if you get into the brakes harder, as onebluemcm ponders, and in a more linear application, seems to have corrected the issue.

I plan on continuing the use of the CoolCarbons until I wear them out or something else necessitates a change. Then I will research a good track pad to put on for each HPDE.

The talks we all had at the track were some of the best I have been around. Just a bunch of Z4M drivers, all with different levels of experience, throwing ideas around.

I did see and sit in, a MC with a full roll cage that did not cut out any of the trim. The driver also gave the the contact info to the guy that built it....

I'll post it later. Just got back and I am dog tired............

[onebluemcm]

Glad to hear it was a successful, safe, fun time. Been reading about horror stories out there - wrecked M5s, P-cars, instructors going off hard - I need to stop, getting 'fraid to drive it out the dang driveway!

[onelove]

Originally Posted by Shipkiller

I did see and sit in, a MC with a full roll cage that did not cut out any of the trim. The driver also gave the the contact info to the guy that built it....

I'll post it later. Just got back and I am dog tired............

Definately snap some pictures! I'm looking to do this before my next event and so far everything is telling me to cut out the bulkhead like the Studie cars, however at that point there is no turning back should I ever want to sell her.

[Shipkiller]

The person who designed and installed the roll cage was:

Mcmahan Autosport, Akron Oh.
rollcageguy.com



I did not take pictures. sorry. I did not take a picture all weekend.

He has two race seats and I did sit in the seats. This setup is NOT for a daily driver. Way too hard to get in and out of on a regular basis.

We talked about his roll cage, then we talked about my front splitter. He wants one....

[onelove]

Originally Posted by Shipkiller

The person who designed and installed the roll cage was:

Mcmahan Autosport, Akron Oh.
rollcageguy.com



I did not take pictures. sorry. I did not take a picture all weekend.

He has two race seats and I did sit in the seats. This setup is NOT for a daily driver. Way too hard to get in and out of on a regular basis.

We talked about his roll cage, then we talked about my front splitter. He wants one....

Because of the door bars or the seat position ? I'm looking to just do a back half cage to alleviate this ?

[Shipkiller]

Originally Posted by onelove

Because of the door bars or the seat position ? I'm looking to just do a back half cage to alleviate this ?

It was a backhalf cage. The seats are the reason that you could not make this a daily driver. The seat tops were very aggressive. The seats were not Sparco's or Simpson. They were a different brand and I can't remember the name. He said that they were a much better fit for a MC than the others.

He also related that you really need to use the VAC motorsports mounts. It just simplifies everything.

[The HACK]

My 2 cents.

I used to run Cobalt XR3s up front and Cool Carbon R/Ts in the rear out of necessity, since the XR3 rears were too thick to fit in the rear (another long story that I'm not going to bother you with). Used to be, on California Speedway's high speed oval, I would get some serious rear end instability especially when we run with the chicane on the front "straight" to turn 2 transition, since you have to brake moderately hard, and if you're stupid like me, trying to hit 140+mph before braking, you would have to be braking REALLY hard to make the artificial chicane.

With the XR3 front, Cool Carbon R/T rear combo the rear end comes "loose" a few times. I chalk it up to the fact that I was trying to brake very hard on a slight bank going straight, but from discussion with fellow instructors it appears NONE of them have that problem. So I sort of ignored it and basically extended my braking zone and not try to be the 140+mph hero thinking the shorter wheelbase must be to blame.

Last year I swapped out the Cobalt for Hawk DTC-60s when the front Cobalts were less than 40% left. Luckily the DTC-60 rears fit the caliper housing just fine so I've been running the same compound front and rear. And surprisingly...None of the squirminess on the high speed bank returned. Brake as hard as I want at speed up on the bank and the rear end feels just as planted as ever. In fact, a pleasant side benefit is that all my tire pressure were EVEN front and rear. When I was running the XR3/CoolCarbon combo the front tires almost always are 2-3 PSI higher no matter how I played with the tire pressure. With the DTC-60 they were SPOT ON.

My theory? The XR3s had much higher brake torque and therefore were forcing the front tires to do most of the work when braking, and far more weight transfered up front than necessary thus resulting in the rear becoming somewhat "squirmy" when braking at a higher threshold.

In my opinion, it is best NOT to mess with the factory "bias" unless you know exactly what you're doing. While shifting the brake bias up front with my combination of pads works for a certain style of driving (it worked GREAT for autocross), same pads all around yield the best result in my experience.

[Shipkiller]

I went back and reread my first post.

I am still trying to figure out how anyone thought I was going to change the brake system bias??? I made no mention of it...

I only talked about pads and going to a grippier pad on the rear.

[Caddyshk]

Stare into my eyes