E92 M3 AP Racing BBK Review (long)

[JAJ]

Originally Posted by rldzhao

One question I've always wanted to ask...

Has anyone experienced pad knock back with the AP Kit on the M3?

Not me!

I had something like it on the stock brakes, but the AP's have been very consistent.

[AP Racing - Chris_B]

Originally Posted by rldzhao

It's because the caliper is now fixed. When you go through corners your discs will deflect and push away the pistons. If the 'knock back' is significant enough you will feel like your brakes aren't working until you step on them again (or more).

Single pot sliders have inherent slack built in so that you cannot really feel the knock back as much.

I would definitely want to hear if anyone is having that issue. It would be completely unexpected as the calipers and strap drive discs both have features to eliminate pad knock back.

There are other offerings on the market that I do hear negative feedback on when it comes to knock back. All I can say is that over many years of development, there are certain tweaks that can be made to avoid it altogether. Well, at least until a wheel bearing starts to go!

The AP Racing calipers used in the Ferrari Challenge Stradale series in Europe are sold in two variants: Tight course (no knock back, but with some very light drag) and high speed course (no drag with some knock back allowed). Teams will run different calipers depending on which track they are running at.

[prodigue]

Where can I order the AP BBK (front and rear) for the E92 M3?

I'm considering between AP and the Alcon Super Kit (380mm)

[STALKER]

Originally Posted by prodigue

Where can I order the AP BBK (front and rear) for the E92 M3?

I'm considering between AP and the Alcon Super Kit (380mm)

I got mine from RennSpec.

[dawgdog]

Originally Posted by prodigue

Where can I order the AP BBK (front and rear) for the E92 M3?

I'm considering between AP and the Alcon Super Kit (380mm)

I purchased mine from WheelSto.

[Neil McRae]

Chris B - your help here has helped me decide to go AP - many thanks.

[RickyBobby]

Originally Posted by AP Racing - Chris_B

It would be completely unexpected as the calipers and strap drive discs both have features to eliminate pad knock back.

Curious what features are in the AP calipers for knockback. Ironically, I ran your AP knockback springs in my stoptech's. They helped, but did not completely eliminate the horrible knockback from the weak nissan hubs. Nothing like coming out of the corkscrew and having your pedal go the floor at the next brake zone.

[Simon@RENNSpec]

Originally Posted by prodigue

Where can I order the AP BBK (front and rear) for the E92 M3?

I'm considering between AP and the Alcon Super Kit (380mm)

PM sent!

[gr8000]

Originally Posted by Simon@RENNSpec

PM sent!

Can you please also send me pricing for the AP slotted BBK kit shipped to Athens, Greece? Please quote pricing seperately for the front and rear kits and a combined quote as well.
Thanks

[AP Racing - Chris_B]

Originally Posted by RickyBobby

Curious what features are in the AP calipers for knockback. Ironically, I ran your AP knockback springs in my stoptech's. They helped, but did not completely eliminate the horrible knockback from the weak nissan hubs. Nothing like coming out of the corkscrew and having your pedal go the floor at the next brake zone.

Oh yeah, turn 9 can pucker the seat cushion if you get a strong run out of 8A and the first half of pedal is surprisingly absent! There is some runoff, but it quickly runs out since the exit is off camber. Not that I have ever had an issue there....

I can't go into all the details, but many years of seal and groove machining variations have essentially eliminated knockback. We often hear that complaint on the ST kits (especially from the Subaru WRX crowd -- much worse than the Nissans), which has *thus far* been cured 100% of the time after moving up to AP.

Chris

[sparkyg]

Dam, such great info Chris, as always thx for being a contributor

[Neil McRae]

Thorney Motor Sport in the UK does AP Racing.

[swamp2]

Chris: How about a more detailed description of "knock back"? What is a design causes it, what does it really feel like. What is really happening with the various wheel and brake components. What designs reduce or eliminate it and how does that work? Thanks in advance.

[AP Racing - Chris_B]

Originally Posted by swamp2

Chris: How about a more detailed description of "knock back"? What is a design causes it, what does it really feel like. What is really happening with the various wheel and brake components. What designs reduce or eliminate it and how does that work? Thanks in advance.

Simplified version (?): Disc brakes perform best when the pads rub lightly on the rotors while the car is moving. This produces almost zero drag (but not exactly zero!) and allows inputs from the driver (pressing on the pedal) to have the most immediate action. As soon as the master cylinder piston starts moving, pressure is built in the brake circuits. This pressure causes the pistons to push the pad's friction material up against the rotor to slow the car. In an ideal world, no work or motion is lost when the driver starts to apply the brakes.

In reality, a whole bunch of stuff is going on to reduce brake system effectiveness and feedback to the driver. The object of the game is to mitigate all these nuisances so the driver doesn't notice the deck is stacked slightly against him.

An issue that has significant ill effects is pad knockback. This is when some action or another has pushed the pads back away from the rotor. Since there is no residual pressure in the brake lines (nor do we want any), the pads will stay away -- or "knocked back" -- until the driver pushes the pedal again. Only now, the first part of the now very soft pedal travel gets used up moving enough fluid to bring the pads back in contact with the rotor. Once in contact, line pressure will begin building to make the brakes work again. It is a very uneasy feeling to suddenly have a soft pedal when it was all good just a moment ago. If there are no mechanisms in place to bring the pads back in contact with the rotor, the pedal problem reveals it's ugly head.

Major causes of pad knockback:

1. Wheel bearing flex: Under heavy cornering, all wheel bearings flex. Some just a little and some way too much! Since the rotor is attached to the hub/spindle assembly, the rotor goes where the inner race of the bearings go. The caliper is fixed to the upright, which stays in line with the outer races of the bearings. When the bearings flex in a left hand turn, the rotors will tilt to the right with respect to the upright. This pushes the pads on the right (front left inner and front right outer) back into the caliper slightly. A right turn does the same to the opposite pads.

2. Cornering G-force: In some professional formulas I've been involved in that use significant downforce, cornering loads are often well over 3g's. If a pad weighs a 1/2 pound, that is now an equivalent of 1-1/2+ pounds pushing the pistons back into the caliper (plus the damned bearing flex!).

3. Vibration and/or shock: In some rally or off-road vehicles, the violent nature of the road surface can jar the pads back into the calipers.

4. Rotor runout: If the rotor is starting to wear unevenly or is no longer in near-perfect alignment with the hat or hat section, the friction surfaces can start to slightly knock the pads away from the rotor.

5. Rotor coning: When some rotors are very hot and run at very high speeds, they will expand in a non-uniform manner. They will start to "cone" around the hat section. This is one of the primary reasons all real race cars use floating, 2-piece rotors. On the street, there are more options to fix this, such as the strap drive system.

Fixes:

1. Design and develop components that reduce or eliminate pad knockback. They may cost a little more, but well worth it. AP has been doing this for years by experimenting with seals, seal grooves, anti-knockback springs behind the pistons and other stuff. Larger, stiffer bearings are a huge expense for most vehicles. Even so, some of the WRX (5-100mm lug pattern) guys move up to the STI hubs (5-114.3mm lugs). The larger, stiffer STI bearings are worth the hassle. Audi A4, Lexus IS300 and late-model Pontiac GTO are more examples of less than ideal wheel bearings.

2. Tap the pedal with the left foot after cornering heavily and before you intend to use the brakes again. This is fun to watch on the track when you are behind someone battling this condition. Well, you might not be behind them for long as most passing occurs under braking.

I vote for solution #1.

OK, this wasn't such a short answer, but I hope it helps. I'm out for a 3-day weekend, so keep on motorin'! May you all enjoy yours, especially if you are working your way closer towards your next deeper brake marker...4...3...2...1(!).

Chris

[swamp2]

^ Great, thanks.

[STALKER]

So I want to get some OEM 18s for my winter set up.
I think it was on this thread, that EU style OEM 18s clear the APs without a spacer, and the North American spec OEM 18s do not.

I contacted Tischer BMW and they say style 219 has one part number, for here and there. So are the style 260 the EU ones?

I don't want to run spacers.

Any help would be appreciated.

Thanks.


EDIT----After some digging. Evan@Tischer was able to come up with the style 260 part numbers. These are the EU spec 18s.

36102283750, fronts, 419.32 each
36102283751, rears, 457.30 each.

[STALKER]

Another Q.
Will the rear OEM 18s clear the front AP BBK with out a spacer?
18x9.5 et23.
Im will most likely get style 260, not style 219(EU VS NA), so it might have a touch more clearance, if any at all.

[Robwe46m3]

Is there any particular reason people are choosing Ap racing over Brembo? i thought that Brembo makes the AP kit???

[STALKER]

Originally Posted by Robwe46m3

Is there any particular reason people are choosing Ap racing over Brembo? i thought that Brembo makes the AP kit???

Brembo owns AP. Diff kits.

I was set to go with Brembo first, but I found more feedback on AP kit, so I ended up going with AP.

[Robwe46m3]

So there are more E9x owners that choose AP over Brembo? Are AP cheaper?

[STALKER]

Originally Posted by Robwe46m3

So there are more E9x owners that choose AP over Brembo? Are AP cheaper?

To be specific, there are lot of owners that have the 380mm Brembo kit, and few run the 365mm kit. I want to run 18s for track and winter, so I needed to get either the 365mm Brembo kit or the AP kit.

AP 368/356 kit is more expensive then Brembo's 365/35 kit. Not by much though.

[AP Racing - Chris_B]

Originally Posted by Robwe46m3

Is there any particular reason people are choosing Ap racing over Brembo? i thought that Brembo makes the AP kit???

AP Racing and Brembo are completely separate business units that compete with each other in several areas and not in others. They are both owned by the Brembo Group (at least since AP was purchased in 1999) and exist in different countries with completely separate management teams. AP Racing is more geared towards racing and low-volume specialty manufacturers. Brembo also does some of this (quite famously in some arenas, I might add!) and is better suited to higher volume manufacturing.

Stillen is the supplier of the systems being referred to here and has been in the brake upgrade business for over 20 years now. They are an AP development partner and system integrator. For some systems, Stillen supplies components back to AP.

Ironically, Stillen was the one to introduce Brembo to the North American aftermarket, effectively creating the industry segment long before most people knew what a BBK was. They made the switch to AP Racing around 1996. The Stillen/AP Racing kits and the AP Racing Formula UK kits are available through at least four forum-supporting vendors.

Chris