24. Performance Friction – Big Brake Kit
You will probably have noticed in some of my reviews that I do drive on the Nürburgring Nordschleife from time to time, as well as on German Autobahn with no speed limits. On the 'Ring but also when braking hard from very high speeds in excess of 170 mph, the brakes of any car are under tremendous stress and have to cope with different requirements than under normal traffic conditions. I had therefor already replaced the stock brake pads with pads from Cool Carbon, which improved the braking response (by making it more linear) and the resistance to heat-induced fading.
During the sportscar driving training of the German car magazine "sport auto" on the Nordschleife in September 2011 where I was doing a lot of rather quick laps on the 'Ring I noticed that at the latest after three fast laps the stock brake system was at its limits, even with the improved brake pads. In particular at the end of these two track days, where the weather was finally dry and I had more confidence in my knowledge of the circuit as well as my car (and I therefor drove faster than before) this was noticeable: vibrations, juddering and squealing signaled that the stock braking system could take no more.
In addition, I knew that I would be upgrading my turbos with RB turbos at the beginning of 2012, resulting in a power bump to more than 500hp. More power = more responsibility errr I mean better brakes required! In particular on a race track a more powerful car also means that you will drive faster in most sections and will therefor have to brake harder at the end thereof (at least as long as the speed in the bends stays identical). Until now I had avoided this last big step of upgrading my car as I knew that a complete brake kit is one of the most expensive investments that can be made for a car.
Which brake kit to take then? There were several alternatives:
- There's StopTech, that has a very good reputation and their brake kit for the 335i was also used by Alpina in their limited edition model B3 GT3. Their kit costs for the front axle (part no. 83.154.6700; 355mm diameter) 3745,- EUR and for the rear (part no. 83.154.004; 345mm diameter) 3103,- EUR.
- Then there's of course Brembo. Their BBK called "Gran Turismo" or "GT" is even available in two sizes as a six-piston kit for the front (355mm and 380mm). It has to be noted though that the bigger diameter results in fitment issues with most wheels, even in 19 inches due to the huge calipers. The smaller version has a list price of 3868 EUR (front) and 3400 EUR (rear).
- Furthermore there is AP Racing who also dispose of an excellent reputation in the brake sector and offer a similar kit for the 335i, again with 356mm and six pistons in the front, but using the stock brake discs for the rear (possibly due to difficulties in fitting the hand brake drum). This Set is sold in Germany among others by ISA Racing and is offered at a list price of 2905 EUR (front; part no. CP5575-09) and 1244 EUR (rear; part no. CP6625-00).
- Finally there is Performance Friction who also have a first-rate reputation for high-end braking systems. Their big brake kit is not cheap either and is quotet at 3600 EUR (front; part no. 1113.0001) and 3400 EUR (rear; part no. 1114.0001).
All of these kits are in principle an excellent choice and a substantial improvement over the stock braking system. At first I had intended to get the kit from AP Racing, as several friends of mine already have it installed on their 335i and are very satisfied with it, even while driving on the Nürburgring. In addition, the AP Racing kit is less expensive and it was possible to further upgrade it by using brake discs from Performance Friction ("PFC"). I excluded Brembo as I found them extremely expensive, and had heard that the availability of spare parts can be a problem with it. The kits from StopTech and PFC are almost as expensive, but I was told from several people independently of each other that PFC uses components of higher quality. The fact which tipped the scales in favour of the PFC big brake kit was in the end that I was offered a used kit that had only by used for one week for testing purposes on a car at a substantial rebate.
Here's a photo of the complete kit (I borrowed some photos from the excellent article from MotoIQ
about the almost identical kit for the 135i):
What are the specific features of the PFC big brake kit?
One aspect that indicates quite strongly to the high-end quality of this kit is the use of a monobloc caliper made out of aluminium. Monobloc kits are usually reserved to motorsport applications and are horrendously expensive for street cars (Brembo offers a kit that goes well into a five figure price, used for example in the Porsche GT3), and it means that the whole caliper is made out of one piece of aluminium instead of two or more pieces being bolted together. An advantage of the monobloc calipers is a far higher resistance against warping, which also means better fading resistance than with two-part calipers. Also, that means that the calipers can be designed smaller, which again is an advantage in weight and compatibility with existing wheels.
Here's a photo of the caliper:
Comparison between stock caliper and PFC caliper:
Each caliper is equipped with four pistons, which may seem paradoxical at first – the standard being rather a 6 piston kit (see above). In principle the more pistons the bigger the pad surface that touches the brake disc, which improves the stopping power. However, other factors also play a role, such as the nature of the caliper (monobloc or two-piece), the size of the pistons etc. PFC has decided to go with a rather unusual design: For each piston there's one small brake pad, which should result in a better initial bite and less taper wear.
You can recognize this feature very well in this photo:
And here are the four brake pads; these are no track-only pads but you can easily use them on a track, as well as in daily driving. For track-only duty it is recommended to use the new PFC08-compound. A replacement set for the front axle costs around 500 EUR:
The rotor has an alloy hat making it about 1.5kg (3 lbs) lighter than stock despite being larger and thicker. The rotor itself is made from a heat and wear resisting, heat treated, high carbon, copper, molybdenum iron alloy. The rotor's ventilation was designed by extensive computer aided airflow, stress and thermal analysis. The directional ventilation system (i.e. the ventilation channels are different for left and right) channels far more air into the rotor, which can mean a temperature difference of between 50 and 100 degrees Celsius. As one can see, the rotor is not drilled, but only dimpled so that there cannot be any fractures between the drill holes, and at the same time also dissipating gases and providing an excellent brake performance in the wet.
Here's a photo of a rotor:
In the following close-up you can see that the bolts simply hold the retaining ring and are not in shear at all:
Another advantage of the PFC kit is that it retains the original rear parking brake which is a separate unit inside the rear rotor, combined with a floating light weight alloy hat:
One of the problems of aftermarket brake kits is that these multi-piston brakes have to use the single hydraulic cylinder of the stock braking system, which due to the bigger surface area of the pistons often results in a poor braking bias and prevents the car's electronic nannies to function properly. That is also one of the reasons why in practice a bigger and more expensive braking system may actually result in longer braking distances and poorer performance of the brakes than with the stock stystem.
PFC however designed their kit exactly around the 335i and its hydraulic system, and the car's weight distribution and suspension geometry were examined as well as the stock hydraulic proportioning. The geometric mechanical advantage of the calipers due to caliper mounting position and rotor size was considered as well to model what the overall brake bias balance would be in static and dynamic simulation. The piston sizing of the Performance Friction calipers was configured using this data to give the proper brake bias.
The installation was done at the same time as my Öhlins coilover at BMSracing e.K. in Leimbach at the Nürburgring. The mounting of the brake kit didn't present any particular difficulties, as the owner of BMSracing had lots of experience with PFC brake kits.
Here's a photo of two calipers – with a bespoke colour in blue:
Installation / front (1):
Installation / front (2)
Installation / front with view onto the caliper:
Installation / rear:
Installation / steel flex brake lines:
And that's how it looks from the outside (1):
The first thing you notice is the turbine-like noise that the brakes make when braking and which is caused by the slotted rotors. I find this really cool and it doesn't disturb me at all – and at higher speeds this is drowned out by other noises anyway.
The pedal feel is far better than with the stock brakes – the initial bite is there, but it is also linear so that with increasing pedal pressure the braking power increases proportionally as well.
The PFC brakes are completely fading resistant. I have not been able to extort any decrease in braking power even when pounding really hard on it during fast laps on the Nürburgring Nordschleife. To the contrary, the harder you strain the brakes, the better it brakes – possibly also a consequence of the brake pads that reach their optimal temperature only after having been used a bit. The same also holds true for several hard brakes from high speeds in excess of 200 km/h on a German motorway – and that really makes me feel much safer than before.
Due to the dimpled rotors, braking under wet conditions is much better than with the stock brakes, which due to their smooth surface often accumulate a water film that subsequently has to be eliminated by the brake pads before they can grab and transmit braking power. This has been much improved with the PFC kit.
There are almost no squealing issues either. With the first set of (used) brake pads that was indeed a slight problem (although nowhere near any full-race-pads-squeal), but this has improved a lot since I had the front pads replaced; now the kit almost does not squeal at all, even at the current very low temperatures.
On a race track, you could of course equip the kit with even more aggressive pads (e.g. the PFC08), but these are in my opinion unsuited to being drivin in public traffic or at low temperatures.
None, really. The only disadvantage is the hefty price tag – including installation you have to count with at least 7500 EUR, and this does not even include (for Germans that is) the work necessary to get it TÜV approved (which is possible but also costs quite a bit). For me however the value for money of this kit is nevertheless excellent, as from other manufacturers you can easily spend double that price to get a kit with similar build and engineering quality. Still, this is certainly only worth the while for those who intend on using their car on race tracks.