It all depends! The first generation MINI Cooper S brakes as sold here in the USA in 2002 are just OK for most street applications. But as is true with all production cars the MINI Cooper S bakes are still a compromise!
From the beginning of production in 2001 until the introduction of the 2007 MINI Cooper S, the brakes in the MINI Cooper were the sake as that found in the MINI Cooper S. As the weight of the cars is the same it was not considered important that the much faster MINI Cooper S needed any better brakes. The problem lies in the fact that with the additional horsepower, people like to use it. Thus we drive faster and need to stop more often from higher speeds.
A street driven MINI Cooper S can expect the stock brakes to last 2 or 3 years depending on driving. The stock MINI Cooper S brakes suffer from only a couple of problems. The first one being brake dust. The stock brake pads are of a compound that seems to shed every time they are used. Thus the wheels of the car are always coated in a black dust. Most MINI Cooper owners change the brake pads for this reason long before the material itself wears out. From my experience the EBC Green Stuff pads are the one to use; no dusting and actually stops better than stock.
The second biggest problem with the stock MINI Cooper S brakes are the rotors. But this is a rather unfair statement as the typical brake rotor replacement is due to owner choice or drive abuse and not a design failure. The design of any brake rotor requires it to sustain some very high temperatures. And for the most part the stock rotors do an OK job for the non-aggressive driver. But even a driver that does not think he is aggressive can destroy a set of brake rotors by poor driving techniques (Braking techniques). Most rotors will warp long before they ‘wear out’. A warped brake rotor is not notable when as you are stopping the car you feel a little vibration in the steering wheel. A warped rotor can often occur under racing condition but still is common on street cars. Any number of circumstances can cause it. If you live in a hilly area and are prone to ridding your brakes down hill and then happen to run through a large puddle of water that could instantly cool the rotors, they could warp. If you use your brakes enough to get them hot and them simply sit an idle for a few minutes with your foot on the brakes, again the rotors could warp. An upgraded MINI Cooper S brake rotor as sold by Mini Mania with slots or holes will decrease the tendency for this to happen.
With the introduction of the John Cooper Works performance upgrades for the MINI Cooper S, the brakes also received some attention. The upgrade kit was an option on all models soon there after. With the introduction of the new 2007 model year for 2007, the previous optional JCW upgraded brakes became the stock brakes on all MINI Cooper S models.
So the now ‘stock’ brakes are indeed an upgrade from previous years and thus do work better on a real street car. But, sadly the reality is that if you ever have a chance to even drive a few laps on any sort of race track, it will fast be evident that a ‘big brake upgrade kit’ is a very welcome addition.