AP Racing, Freaky Parts, 996, Cooling? School me on BBK to help pad consumption

[George Hill]

I'd put money that most all stock calipers, brass or (especially) stock bushings, have this movement to some degree when there are no pads installed.

I would agree, the spring clip helps counteract this but the solid guides I would think shouldn't need.

I am no expert on the solid guides so I don't have an opinion on them in this situation. But just as an interesting note on pad taper or to compare these are my DTC-60s with stock rubber guides, lol.

[Pklauser]

Yea Bimmerworld actually says to forego the spring clips with their guides. Appreciate that comparison! I'd say those look nearly identical to my taper. Mine also have radial taper, from the inside of the rotor to the outside, not sure if you have that as well. Are you tracking with the rubber guides?

[George Hill]

It does have some slight radial taper but nothing as much and significant as photographed.

Yes, rubber guides and this is a 330 rotor/caliper, but the uses the same M3 pad. The car does have an S54 and will do 140+ at CoTA so I feel it is relevant. I had stayed with the rubber guides as I was concerned with stiction from brass guides, but I can't imagine it would be worst than this, lol.

After seeing these pads though I am now looking into changing my braking setup and will likely go with a radial mount caliper.

[Pklauser]

Here's my taper for reference. IMO as bad if not worse than the rubber guides.

[mrgizmo04]

You can never fully escape taper. I had some slight taper on my st40 kit, I had taper on 996 kit, I know people get taper on AP kits as well. I haven't seen radial taper much though.

With brass guides you have to relube them pretty frequently. Yours almost look like they get jammed and don't slide freely and then they twist the whole caliper.

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[mrgizmo04]

To talk about cooling...

Most important part of a brake setup for cooling is the rotor. It is the only "air pump" that actually evacuates the heat. Sure you want a bigger rotor (more iron mass/more heat capacity like increase in thickness, not necessarily only bigger diameter), sure you want a pad that 1) is made of material that can handle the heat and doesn't melt at 500 degrees like street oriented pads and 2) is physically larger to increase heat capacity. Increasing heat capacity is good to a point because at some point it still gets oversaturated (think of filling an espresso cup with water vs a mug with water, mug can hold more water but at some point it still gets full) and heat dissipation rate is lower than heat generation, so you need heat evacuation, where the design of the rotor comes in.

Stock non ZCP rotors I would argue are better at heat evacuation than CSL rotors due to weird semi floating CSL design and hat curvature. All the air you point at a CSL rotor hat just deflects it back and it is actually hard/impossible to force the air into the small space between the hat and the ring to the two inner rotor faces to get the heat out.

Heat transfers in 3 ways, but in brakes mainly via conduction and radiation. Radiation is where you put your hand next to a stove (not touching it) and you feel the heat radiating. Rotors and pads radiate a lot of heat but there needs to be an open path for that heat to go. This is where removing (or at least trimming) the dust shields helps a lot and having wheels with more open spoke design also helps. This is super important for the rears since there is no easy way to cool them due to parking brake surface. Conduction is when you put a lighter on the end of a rod and in a few seconds your hand holding the other end starts getting burned, since the material you are holding transfers the heat through it. From the surface of the pad in contact with rotor, you get conduction via 1) the pad to the backing plate to the piston to the fluid 2) rotor surface to inner veins to hat.

You want heat barriers, or parts that would slow down conduction, ones that have poor thermal conductivity. Aluminum is very good at conducting so therefore a very poor barrier. Titanium is very good barrier, steel is ok, aluminum is poor. Most calipers use aluminum pistons - cheaper to produce but will conduct heat easily and help boil your fluid. AP I believe use steel pistons to help fight this. I use titanium shims (a plate that is shaped like the backing plate that sits between the pad and the pistons). Hardbrakes.com, girodisc make them for different pad shapes.

Back to the rotors and pumping heat out. Proper bbk designs have a hat that mounts to the outside of the rotor so that all the air that makes it into the hat can be pumped out via rotor veins between the two rotor surfaces, evacuating heat from both inner and outer surfaces and cooling them. CSL rotor/e90/f80 design is pretty bad at this as I mentioned before (listing e9x and f8x since I know folks "upgrade" to those). Forcing air into those rotors helps cooling (entire system like rotor, pad, caliper, fluid, not just rotor) tremendously and makes the rotors and pads last a lot longer. This is where convection comes in. Normally blowing air onto internal surface of the rotor is a big no no as that only cools one side and bends the disc since exterior surface stays hotter which results in stresses and cracks. What I found with CSL rotors is since they have swiss cheese design, blowing air onto inner surface actually makes the air blow though to the outer surface as well (at obviously lower rate) to cool them. Not ideal, but it seems to work. That said I run Vorshlag deflectors, which are tall enough to route air into the center wheel bearing as well as inner surface (I trimmed my dust shield). I used to run hoses to the center of the hat, but per explanation above CSL rotors would not get cooled enough due to hat design. I saw 100-200 degree cooler temps switching from hoses (granted I ran 2" routed via underbelly which became a pain to remove the underbelly) to Vorshlag deflector. With a proper BBK that has good rotor design (ST40, AP) you might not need hoses or extra air forced into it since the rotor hat/vein design is efficient at evacuating heat.

I will say though as a general observation from my personal "testing" that even when I ran ST40 (which has efficient rotor), running extra cooling prolonged the life of the pads and rings. Granted YMMV, and your track sessions could be different, but I run mainly open days where your session can last hours with just a break for lunch. For "regular" 20 min sessions you prob won't need extra cooling (like example of espresso cup vs mug), a proper bbk might have enough capacity for a short stint. Do use readouts/paint/fade/feel/etc to guide your decisions.

Last point I'll mention is brake less. VERY hard to do when your brain is constantly trying to protect you and you doubt that the car will make it around the bend. You should brake harder but shorter and in a lot of places where you "comfort" brake you can stop doing it. Trust the grip, it's there, find it, it's a journey.

Ok, per usual, I don't know what I was babbling about, hope some of it makes sense.

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[mrgizmo04]

On the topic of extra thick pads and other setups.

Brake setup that runs cooler and more efficiently will make components last longer. Whether you achieve that by getting a 380mm 6pot kit with thick pads to increase heat capacity or more efficient kit (proper vented rotor even something like Girodisc for stock setup over CSL/e9x/F8x rotor), or force ducts/hoses/deflectors to shove air at it, can all at the end of the day perform equally well.

It is also a dynamic spectrum for how YMMV throughout the life of the kit. You get a new kit, run it on track and things feel awesome and you are super happy. Fast forward x events into the future when the discs are a mil or more thinner, the pad is below half life and the heat capacity of your kit naturally decreased. You might start experiencing problems. Up to you to find optimization to the problem - replace pads/rings a bit prematurely because you start having issues at half life, look at additional cooling, add thermal barriers, upgrade to a bigger/"better" kit, etc. Ideally you want to optimize for not having any issues when rings get to min thickness and pads only have a smear left of material, but not many get there.

It is a personal journey, so there is no single answer, (like everyone should not just buy AP, for most it is overkill). Energy your brakes have to dissipate is .5*m*v^2. You might lighten your car, you might get more comfortable with the track and your speeds will increase but you can also be more comfortable and rely on tire grip and rotation, you might add aero (and drag that will slow you down) and might not need brakes (as much).

Braking technique is a very complex topic, it's not just mash as hard as you can as late as you can. Release is most important to settle the car on entry, so there is a lot to be gained getting coached on good technique. Speed Secrets Ross Bentley has some good materials on this.

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[elbert]

Mine also have radial taper, from the inside of the rotor to the outside, not sure if you have that as well. Are you tracking with the rubber guides?

IME radial taper with the stock setup is normal. What happens is the outer portion of the friction ring gets hotter than the inner part -- thus it expands more and is subject to more wear. As things cool down, you will see it as uneven radial wear.
This becomes much more apparent as the rotor wears and has less heat capacity.
I had this happen with brass bushings

I would also recommend you consider replacing your pads at the halfway point (or just past it) with the stock single piston setup.
As the single piston extends out of the caliper, it (and the pad) will move around more.
edit: It is also at that point I tend to see more issues with the "tabs" or "ears" of the pad binding on the caliper and bending, not sliding like they're supposed to be doing. Boots tend to get torn up more too as they're extended.

I am a firm believer of replacing the rotors and pads together. If one goes, the other gets replaced too. If the one part is in reasonable good condition, keep it as a spare/backup.

[mrgizmo04]

On the topic of cheap BBK kits from Freakyparts or Signaturewerks and the like. They used to offer more kits, some of them got taken down...

I am not going to badmouth or spread any information I got second hand from trusted sources, but I invite you to do some deep research into the weeds of other forums and Facebook groups. Some key questions like how/where the parts are sourced, how they are made, how they are cast (!), are they actual Brembo off the cars they are claimed to be off, how they are turned to be radially mounted, who got paid to pump these "kits", etc.

There is a reason these Alibaba kits are cheap. I am going to park this as food for thought here. There is a huge movement in BBKs that folks want mainly for looks, of course companies will find a way to satisfy the demand.

Also a lot of stories of cheap AP kits making rounds that don't fit or work properly that are not directly from Essex.


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[Pklauser]

On the topic of cheap BBK kits from Freakyparts or Signaturewerks and the like. They used to offer more kits, some of them got taken down...

I am not going to badmouth or spread any information I got second hand from trusted sources, but I invite you to do some deep research into the weeds of other forums and Facebook groups. Some key questions like how/where the parts are sourced, how they are made, how they are cast (!), are they actual Brembo off the cars they are claimed to be off, how they are turned to be radially mounted, who got paid to pump these "kits", etc.

There is a reason these Alibaba kits are cheap. I am going to park this as food for thought here. There is a huge movement in BBKs that folks want mainly for looks, of course companies will find a way to satisfy the demand.

Also a lot of stories of cheap AP kits making rounds that don't fit or work properly that are not directly from Essex.


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I think the value of the forum is to share information like that. If you have trusted sources saying the Freakyparts kit is bunk, please do let us know where to find that info.

[r4dr]

As far as I know, the Freakyparts Megane RS caliper kits are legit. Where it gets sketchy are these other outfits which take GM Brembos (readily available for cheap), machine the lug mount portion off, and drill into the caliper body to convert it to a radial mount.

100% sketchy and I wouldn't trust that. There are a ton of garbage BBKs out there.

[Pklauser]

As far as I know, the Freakyparts Megane RS caliper kits are legit. Where it gets sketchy are these other outfits which take GM Brembos (readily available for cheap), machine the lug mount portion off, and drill into the caliper body to convert it to a radial mount.

100% sketchy and I wouldn't trust that. There are a ton of garbage BBKs out there.

Yea I think the one thing that's maybe sketchy is that the brackets use bolts instead of studs. I've heard that generally studs are more reliable in this application, hence Essex using them in their AP kits. But also our floating stockers technically use bolts in the form of the sliding pins sooooo

[heinzboehmer]

The reason I suspect my rotors are tapered is that when I put on my street pads, I end up with a rust ring in the center of the outside face of the rotor. The street pads themselves do not appear tapered. Another interesting data point against wheel bearings, not saying they aren't contributing at all, is that my pedal is garbo even just going straight down the road without double-tapping.

On the subject of brass bushings. This is how much movement the calipers have on the Bimmerworld brass bushings. Maybe I'm misunderstanding something, but this seems like a lot, and doesn't seem like they would do a great job of preventing taper.

https://youtube.com/shorts/f9TZ4fejAy0?feature=share

Swapped pads today and remembered this thread. This is the play that my stock calipers have with no pads, ECS bronze bushings and sliding pins torqued to spec: https://youtu.be/Kl0GjZjVaAI

There is some play, but nowhere near as much as on your car. You can see in the video that most of the play is between the bushings and the caliper, which is what I expected.

[Pklauser]

Swapped pads today and remembered this thread. This is the play that my stock calipers have with no pads, ECS bronze bushings and sliding pins torqued to spec: https://youtu.be/Kl0GjZjVaAI

There is some play, but nowhere near as much as on your car. You can see in the video that most of the play is between the bushings and the caliper, which is what I expected.

Wow! That's immensely different! I emailed Bimmerworld and they effectively told me to pound sand, I bet they'd be very interested to see your video. Are those the ones that need to be pressed into the caliper like these? https://www.ecstuning.com/b-ecs-part...003326ecs01~a/

[heinzboehmer]

Wow! That's immensely different! I emailed Bimmerworld and they effectively told me to pound sand, I bet they'd be very interested to see your video. Are those the ones that need to be pressed into the caliper like these? https://www.ecstuning.com/b-ecs-part...003326ecs01~a/

Yep! Those are the ones I've got