"These entries are part of a Special Series on the development of the M3 V8's Bespoke AP Racing Clubsport Brake Kit. 

This specific journal entry tackles the first kit in the lineup: the Clubsport front kit and touches on the development mindset, goals and hardware selection of the kit."
- Matt

My Stripper build objectives

My Stripper E92 M3 is not a track car, it has barely seen the track - and it barely will. Valuations have gone crazy and the unfortunate truth is I can't flush that value down the toilet. 

I aim at creating an ultimate response program for the E92 M3. 

My goal is to optimize for lightweight, OEM+ appearances, improved feel, reasonable cost, easy  access to replacement parts and the thermal capacity for track use should I wish to go ham. 

I've been looking at partnering up with a reputable brake company prior to EuroConnex's existence.

It's a difficult market that covid made a lot of worse.

Most companies were notoriously backordered for over a year and weren't taken on new projects. I also previously attempted a 50+ member group buy with SlonWorkshop only to see it failed due to his inability to deliver the kits en masse. 

HaimusRacing's Development Mindset

Antonio and his team develop parts for their own race cars first, and selling them is an auxiliary objective. The Clubsport kit is a project they began developing for their E92 M3 Clubsport build. 

This has a lot of good, and some bad: he often underestimates how popular his products can be. 

Bigger is better! Eh not quite. 

The market has many six piston kits with 380mm front rotors. The benefits of 6 piston kits is a larger rotor, and bigger pads. This usually leads to more heat dissipation, a mission-critical requirement for endurance racing.

However these thresholds are very rarely met. This isn't needed for most situations: it is more weight, and more expenses. 

Haimus is developing a 6 piston front kit for those who want the maximum thermal capacity for endurance racing. 

For most of us: 6 pistons are overkill. It most definitely is for me.

The development backstory to the 4 piston Clubsport kit. 

HaimusRacing runs and supports various Clubsport cars running in series across Eastern Europe. They notably run their own E92 M3 Clubsport as a test bed for the development of new products. 

They have been running 4 piston calipers upfront on 3 of their racecars which weigh over 1.6 tonnes / 3,500 lbs for two seasons on the track. 

They have hands-on results to show for. 

Antonio's optimization targets with the Clubsport kit 

The main goals for their Clubsport system were audacious:

1. Lightweight
2. Improved braking performance
3. Street friendly and track suitable
4. Superior brake bite and brake feel
5. Improved heat dissipation 
6. Accessible, affordable consumables

The Foundations:
New AP Racing Hardware

In order to achieve their goals, HaimusRacing had to chose the right components. AP Racing was the natural brand to be selected due to their proven quality and HaimusRacing's long standing relationship with the company. 

Caliper selection:
 4 Pistons RadiCal-2 

Antonio's team selected the AP Racing's 4 pot radical-2 CP9540 caliper for key reasons. 

It's light, and strong. 

The caliper is forged 2 piece aluminum alloy weighting in at 3.5 kg. It is engineered with with similar stiffness, clamping force and performance of a racing caliper, but retains its street friendliness. The AP caliper uses high quality, lightweight racing pistons.

It's slightly heavier than a racing application Pro500R who isn't suitable for street usage. 

It's street friendly. 

The caliper is equipped with high temperature piston dust covers, which allow usage of the item in dusty, salty conditions.

The calipers also come with anti-rattle clips. They sit between the pads and and the brackets to dampen noise and vibrations. 

It's cost effective. 

The caliper is also cost effective, while providing all the targets Haimus sought to achieve. Eventual rebuilds have easily accessible parts from AP Racing. 

It has popular pad replacement options. 

The caliper uses the pad shape CP6600D55. For track only use, AP has multiple track focused pad material options. 

My kit was delivered with APF404 pad material. AP describes it as their most track suitable pads that can be used on the street.

This pad shape is available from various popular manufacturers like Endless, Pagid and Ferodo. 

Brand	Reference Number
Ferodo	FRP3083W
Endless	RCP100
Pagid	4345 / 20345

It has extensive rotor ring options. 

The caliper can be used with a wide array of easily accessible performance rotor rings, which are available from multiple companies such as AP Racing, Tarrox, DBA, Alcon and others – allowing us to have many when picking replacement rotors.

It meets specific e9x M3 technical brake requirements.

The overall piston area is 49.56 square centimers. It is a bit smaller than the stock single piston at 56.56 centimers.

The multi-piston AP Racing caliper has much higher efficiency than OEM. They are staggered diameters at Ø38.1mm and Ø41.3 mm. 

The pistons of the caliper sit higher on the rotor than the stock caliper does. Both of these specifications change the center of pressure.

In short, this means improved brake response while slightly shifting the bias to the rear. 

Antonio and I will touch on why they opted for this shift in brake bias in the next journal entry.

Rotor selection:
 AP Racing 362x32mm Semi Floating Rotors 

HaimusRacing's engineering team wanted a rotor size and bolt pattern (PCD) that was supported by multiple performance brake companies for a wide range of performance and cost options. 

A bigger, lighter rotor. 

The size checked all the boxes was the AP Racing CP4542-142/143.  The rotor 362x32mm. It is bigger than the stock rotor by 2mm and wider by 2mm as well. They come in at 7.8 kilograms without the bells. 

With the bells fitted to the rotors, the assembly is approximately lighter by 2kg per side than the OEM rotors. 

Improved Ventilation. 

The Genuine BMW rotors are notoriously poor at dissipating heat and will have accelerated wear under track conditions as it goes beyond its thermal dissipation thresholds. 

A critical selection criteria was the ventilation technology from AP. The 48x venting tunnels within the rotor are much taller than stock, providing increased heat dissipation capacity.

It's street friendly. 

Antonio selected a semi-floating rotor configuration to optimize for street friendliness over ultimate track use.   

The main component to the street friendliness of a 2 piece rotor is its attachment to the bell.  

• The semi-floating rotors are attached to the bells using bolts. 
• The floating rotors use bobbins. 

 

The semi-floating attachment using bolts. 

What are bobbins? 

Brake manufacturers always assume we know.

In short: they're the bolt-looking hardware holding floating rotors to the bells. They are designed to allow for "float" between the rotors and the bells.

Floating rotors are the ultimate in performance as they allow thermal expansion of the braking system under extreme use, reduce chances of warping and slightly reduce pad wear. 

HaimusRacing has experiences with fully floating rotors, notably with a regional rally team. These cars will see dirt, rocks and debris - surely more intensively than the street, but we all get our fair share of crappy road conditions. 

They had the issue of debris and small rocks sometimes getting into the bobbins and destroying the bells. 

Floating rotors will start making noises after a couple of thousand miles with 3-4 track days in between when the bobbins get fully bed in.

The bobbins and rotor bells need replacing every 2-3 rotor changes, adding considerable running costs for track oriented Clubsport owners. 

Most E9x M3 owners know of the infamous pebble-in-the-heat-shield noise often experienced. Bending a heat shield is easy. Replacing expensive rotors and bells isn't.

This rotor is cost effective. 

Haimus was adamant about using a rotor that has the latest ventilation technology, was lightweight, easily sourced while being mindful of replacement costs. 

The rotor rings can be sourced for roughly 595 US. 

 

Up next: we take a more technical dive on brake bias, ABS and real-world results.