Pad fade normal?

[ABenLauda]

Hey folks,

I ran 2 back-to-back 30 min sessions and 10 min into the 2nd session, I had pad fade. Entering a braking zone, I squeezed the brakes hard and the car did NOT scrub speed like it used to (in the last 40 min) and I took her straight into the grass. Is pad fade normal? I'm on OEM rotors/calipers and PFC11 pads. This is the 1st time I'm doing 2 x 30 sessions back-to-back with no cooldown, so I've never experienced this before.

NOTE - This was not fluid fade as my brake pedal was decently firm throughout the session.

What's the solution to this?

Any advice is greatly appreciated. TIA.

[SYT_Shadow]

Pad fade doesn't happen on pfc11s, but two sessions back to back with a CS is way too much for a stock system

If you don't want to spring for a bbk, get the girodisc rotors that will extend the oem brake life

[NYG]

PFC11 will operate up to 1500F so you didn't get pad fade.

This is VERY likely boiled fluid and your firm pedal is the result of your stainless steel brake lines.

Unfortunately, this is something you will continue to struggle with until you upgrade to a BBK or you can go the more difficult route and establish airflow to the front brakes. The entire front grill is a wall of radiators so that won't be an easy task without penetrating into the front bumper and I doubt you want to do that to your MY2020 CS - I didn't.

You can attempt to mitigate the heat generated by doing a couple of things:
1. Switch to rotors with less mass and better ventilation
2. Switch to a less aggressive pad - the PFC11 stops harder than any other pad that I've used
3. Switch to a less grippy tire if you're using an R compound

But IMO, those will just be a waste of time and a detriment to performance. Lack of airflow and the front calipers are just not up to the task.

[ABenLauda]

Originally Posted by SYT_Shadow

Pad fade doesn't happen on pfc11s, but two sessions back to back with a CS is way too much for a stock system

If you don't want to spring for a bbk, get the girodisc rotors that will extend the oem brake life

Can I upgrade just the fronts to girodisc and keep the rears OEM? Any braking stability issues with this?

Can I still use OEM calipers with girodisc rotors?

[SYT_Shadow]

Originally Posted by ABenChod

Can I upgrade just the fronts to girodisc and keep the rears OEM? Any braking stability issues with this?

Can I still use OEM calipers with girodisc rotors?

I believe, but am not certain, that Girodisc makes an oem conversion kit. The fronts are where most of the braking takes places, so I would prioritize that.

The conversion kit continues to use the rest of the OEM setup, so the calipers and pads do not change.

I would also try to get some titanium shims for the calipers. With that plus girodiscs you are in a good place. Maybe you'll need those high temperature brake seals someone sells for the OEM calipers.

At the track this weekend there was a reasonably fast GT4 and he was already using a full girodisc conversion despite his braking system being more track ready than what you get in a F8X. The M4 CS has way, way more power and weight so the demands on the braking system are massive. It sounds funny, but it's not easy to picture an OEM system that can take what the F8X delivers.

[NYG]

Originally Posted by SYT_Shadow

It sounds funny, but it's not easy to picture an OEM system that can take what the F8X delivers.

^ this.

And if you're on stock suspension, lack of stiffness on your springs will overload the front even more.

Extremely fast + moderately heavy + soft springs + weak calipers - air flow = Thermonuclear Brake

[HA55L3R]

Originally Posted by ABenChod

Can I upgrade just the fronts to girodisc and keep the rears OEM? Any braking stability issues with this?

Can I still use OEM calipers with girodisc rotors?

I'm currently using the girodiscs (only in the front) with titanium shims, pfc 11 pads, racingbrake dust boots and cooling ducts. They do a much better job at cooling than the OEM rotors and my pads are lasting longer. No stability issues and the brakes don't fade as quickly.

The stock brake system doesn't like being overworked, it helps to dial it back a lap or two mid session to give things a chance to cool down

[CanAutM3]

Originally Posted by ABenChod

Hey folks,

I ran 2 back-to-back 30 min sessions and 10 min into the 2nd session, I had pad fade. Entering a braking zone, I squeezed the brakes hard and the car did NOT scrub speed like it used to (in the last 40 min) and I took her straight into the grass. Is pad fade normal? I'm on OEM rotors/calipers and PFC11 pads. This is the 1st time I'm doing 2 x 30 sessions back-to-back with no cooldown, so I've never experienced this before.

NOTE - This was not fluid fade as my brake pedal was decently firm throughout the session.

What's the solution to this?

Any advice is greatly appreciated. TIA.

As another possibility, is it possible that the car was not completely straight (steering wheel still slightly turned) when you started braking when the event occured?

I’ve learnt that the ABS/CBC does not like hard braking while turning. I have a corner at my local track that has a very short braking zone and if I make the mistake of being hard on the brakes before the car is well settled in a straight line, the ABS will prevent hard braking regardless how hard I press on the pedal. Quite unnerving

[r4dr]

There's a fair amount of misinformation in this thread... if the fluid boiled, you wouldn't have the "pushing hard on the pedal but the pads are just sliding" feeling. Air will feel like air regardless of if your lines are SS or OEM, lol...

You can certainly do front Girodiscs only, they are direct replacements for stock so no changes in brake bias or anything like that. They will help but that is a mitigation approach -- you're just punting the problem farther down the road.

Which is fine for DE sessions, but may not be fine for something like endurance racing. Do some cooldown laps if you must. It's tempting to go ham for 60 minutes of lapping with no break, but without ducting these cars will hit a wall at some point. Metaphorically, not literally. Poor choice of words, perhaps.

[BMMMW14]

Throwing in my 2 cents here... had a very good result in switching from stock rotors to Girodisc on my F80 tack car. Two days at the Glen, running each time until out of fuel, and it's the first time the PFC 08 pads didn't crack and wear was far lower than prior. Agree with comments above with those pads, pad fade is unlikely. That with fresh Motul 660 and led to no problems... granted this is now down to ~3,450 with cage. The extra 2mm of thickness and huge amount of vanes led me to give it a shot over dropping $9k on a full race system. You can see the difference pretty clearly in the first pic, sorry don't have a close up of it mounted. Happy for now.

[NYG]

Originally Posted by r4dr

There's a fair amount of misinformation in this thread... if the fluid boiled, you wouldn't have the "pushing hard on the pedal but the pads are just sliding" feeling. Air will feel like air regardless of if your lines are SS or OEM, lol...

In general, you're correct but a soft pedal is not exclusively the compression of air in your lines. The expansion and stretching of rubber lines reduces hydraulic pressure significantly which also affects how much of the air you can actually compress. So if you apply the same pedal force, a stainless steel brake line with air will have higher hydraulic pressure than a hot rubber line with air. It's not misinformation, it's classical mechanics.

I'd agree with you in 99% of cases but overheating a PFC11 is not an easy task even on the F8x.

[CanAutM3]

Originally Posted by NYG

In general, you're correct but a soft pedal is not exclusively the compression of air in your lines. The expansion and stretching of rubber lines reduces hydraulic pressure significantly which also affects how much of the air you can actually compress. So if you apply the same pedal force, a stainless steel brake line with air will have higher hydraulic pressure than a hot rubber line with air. It's not misinformation, it's classical mechanics.

I'd agree with you in 99% of cases but overheating a PFC11 is not an easy task even on the F8x.

The pressure/force does not change. It's the displacement that changes.

[USSEnterprise]

NYG and Shadow always swear OEM system isn't up to snuff. It's pretty much the only topic on the board I disagree with them on (OK, other than shadow's blind unproven love for the G80 lolll). OEM system is perfectly capable AS LONG AS YOU GET THE 6 PISTON FRONT AND 4 PISTON REAR M2C calipers and then upgrade to Giro Disc rotors. I have the CCB system that has the gold 6/4 piston calipers and switched out carbon rotors to Girodiscs. I cannot overheat my system even if I tried.

Before spending all the cash on a BBK, I would just get the 'factory BBK' and if you are really keen, get the girodiscs. Girodiscs pay for themselves in the long run as you only replace the rings. Again, this is if you do 20-30 track days a year or more.

Here's a really good post by a member that breaks down all the M2C caliper options (he even quotes a thread I made on this topic haha). https://f80.bimmerpost.com/forums/sh...&postcount=173

He says all the varieties of the 6 pot calipers have SS or Titanium pistons (as opposed to aluminum). That's very telling, if true. Caliper pistons make a HUGE difference in heat management.

In every single race bike I have, swapping out the aluminum caliper pistons to SS is one of the first mods. Adding titanum or aluminum shims with radiator fins between pads and calipers is another mod - see second pic below. I spend a ton of time managing braking system heat on bikes, so here's a few pics.

[m4forum]

If there is a topic i am getting familiar with is BBK. There are a lot of good advises already on this thread but I can help with some of my experiences.
I have experienced brake loss at Watkins Glen on back straight which was cause of extreme high temperature on stock brake system and as consequence brake fluid boiled. I had the temperature sticks on my calipers to confirmed that. Potentially you experienced the same issue.

What is the solution : increase thermal capacity of your system AND heat dissipation which can be achieved by:
1) increasing rotor thermal capacity -> limited to rotor size on stock
2) increasing heat dissipation where the heat is generated -> Girodisc can help due number of vanes.
adding cooling ducts can help but needs to be done correctly. 90% what I see posted on the forum doesn't do much as there is 90 degree bent on the circuit which drops the air speed by 67% so no much air gets where it needs to. I measure it and tested what doesn't work. At Watkins Glen I had my initial braking cooling including the rear ..... didn't help much as I boil Motul 600.
2) improve thermal barrier between pads and brake fluid. here you can replace the original aluminum pistons by SS (Racing brakes have them). Also can add pad shims. It should help with the pedal feel

The major question is ho much improvement you need based on tracks, skills and tires used. It will all depends and most likely only you will be able to answer based on the improvements can achieve with the alternatives listed.

Personally I believe stock M4 system can be improved but not enough to handle Watkins Glen on R compound and laps below 2:08. M2C can be a good alternative at $4.5k but will restrict you from using 18" tires what is a big deal for me. I decided to go with BBK on front only (allows me 18" tires) but with M2C on rear so total I spent $6.8k and have system that should be capable of handling more that what I need.

[NYG]

Originally Posted by CanAutM3

The pressure/force does not change. It's the displacement that changes.

So you apply a force to the brake pedal. The fluid displaces toward the pistons right?

Compressing air requires energy right?

Deformation of the rubber line requires energy too.

Now instead of having an applied force and a single reaction at the piston you have an applied force + compression of fluid + hoop deformation.

[NYG]

Originally Posted by xxaarraa

OEM system is perfectly capable AS LONG AS YOU GET THE 6 PISTON FRONT AND 4 PISTON REAR M2C calipers and then upgrade to Giro Disc rotors.

Lol, I love you too bro but that's not OEM.

Shadow and I probably have a lot of the same experiences partially because we like PFC pads. Those mf make a serious pad.

[CanAutM3]

Originally Posted by NYG

So you apply a force to the brake pedal. The fluid displaces toward the pistons right?

Compressing air requires energy right?

Deformation of the rubber line requires energy too.

Now instead of having an applied force and a single reaction at the piston you have an applied force + compression of fluid + hoop deformation.

Yes, and energy is a function of displacement:

Energy = Work = Force x Displacement

But you cannot confuse force and energy. For a given force applied to the brake pedal, the same amount of force is applied on the brake pad regardless of how much the fluid compresses or the lines expand, that's basic fluid dynamics. Energy gets transfered to the compressed fluid and expanded lines but it does not alter the force being transmitted, just like with a spring. The pedal will however travel farther for a given force when there is more fluid compression and/or line expansion. That's why the pedal gets long/soft when the fluid boils. At the extreme, the pedal travels all the way to the floor before being able to transmit sufficient force to clamp the brakes. That's when fluid fade becomes scarry .

[CanAutM3]

Originally Posted by xxaarraa

NYG and Shadow always swear OEM system isn't up to snuff. It's pretty much the only topic on the board I disagree with them on (OK, other than shadow's blind unproven love for the G80 lolll). OEM system is perfectly capable AS LONG AS YOU GET THE 6 PISTON FRONT AND 4 PISTON REAR M2C calipers and then upgrade to Giro Disc rotors. I have the CCB system that has the gold 6/4 piston calipers and switched out carbon rotors to Girodiscs. I cannot overheat my system even if I tried.

Before spending all the cash on a BBK, I would just get the 'factory BBK' and if you are really keen, get the girodiscs. Girodiscs pay for themselves in the long run as you only replace the rings. Again, this is if you do 20-30 track days a year or more.

Here's a really good post by a member that breaks down all the M2C caliper options (he even quotes a thread I made on this topic haha). https://f80.bimmerpost.com/forums/sh...&postcount=173

The main drawback of the 6/4 piston OE solution with iron rotors is a rather non negligible ~35lb increase in unsprung mass. A good aftermarket BBK will offer similar if not better performance without the weight penalty.

[m4forum]

For the front there is a big increase in weight but for the rear not.
Stock M4 rotor + caliper : 28.32 lbs
M2C rotor + caliper : 28.15 lbs

[swagon]

ITT: seasoned track bois for whom no stock brake sytem is enough.

I think if your name is not Kubica and don't do one-hour plus stints at 10/10ths, the OE iron kit is enough.

I'm a track newb and still managed to cook OE pads on a rainy day with DSC on. Just Ferodo pads and a fresh BMW fluid made a very noticeable difference; now I've got RBF660 in. Girodiscs next as OE rotors are getting past their prime and I like a bit of weight saving.

Also, personally, I see no fun or point in hammering down the straight at 150 mph only turn into a 30-mph chicane if I'm losing more time in another sections of the track. Might as well lift off, let things cool down a bit and manage to also travel back home at the end of the day.

[CanAutM3]

Originally Posted by m4forum

For the front there is a big increase in weight but for the rear not.
Stock M4 rotor + caliper : 28.32 lbs
M2C rotor + caliper : 28.15 lbs

Not sure where you're getting your info, but I find ~34.4lb for the big M2C rear brake (rotor+caliper+pad). The M2C rear big brakes sure aren't lighter. Comparing "blue" stsndard F8X iron brakes to "grey" M2C brakes:
Front +11.5lb per corner
Rear +6lb per corner
Total +35lb

[USSEnterprise]

Originally Posted by CanAutM3

Not sure where you're getting your info, but I find ~34.4lb for the big M2C rear brake (rotor+caliper+pad). The M2C rear big brakes sure aren't lighter. Comparing "blue" stsndard F8X iron brakes to "grey" M2C brakes:
Front +11.5lb per corner
Rear +6lb per corner
Total +35lb

I think 35lbs is way too high of an estimate.

I weighed my girodiscs vs CCBs. Here: https://f80.bimmerpost.com/forums/sh...5&postcount=20

So, 6 pot/4 pot calipers and steel rotors are only ~46 lbs heavier than carbons. Which means they cannot be 35 lbs heavier than OE 'small' steel brakes. Otherwise, it would mean you are saying OEM 'small' steel brakes are only 10 lbs heavier than carbons, which is simply not true.

The smaller calipers and steel rotors will be lighter than M2C OEM BBK, but not that much lighter. My guess is its about a 10-15 lbs weight penalty at best. Which on a 3650 lb car, not even a pro driver is likely to notice.