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      04-03-2014, 09:39 AM   #21
ChipB
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Drives: 2015 M4 'vert, 2014 X5
Join Date: Nov 2010
Location: Naperville, IL

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Quote:
Originally Posted by rhonig View Post
Your mods look great! Is there a great improvement in the braking ability of the vehicle with the ///M brake kit?
Atomic80 didn't answer this, but I'd be surprised if the answer is yes. There are several factors that affect the ability of the brakes to slow the car:

1. Tires. In almost all cases the limiting factor is tires. If you jam on the brakes in an emergency stop so that ABS kicks on, that means the tires are sliding - in other words the power of the brakes is overwhelming the traction available from the tires. So to improve braking the first step is to improve tires.

2. Brake Pads. Under repeated high speed braking it's possible for the brake pads and calipers to get very hot. Stock brake pads are a compromise design to keep the brakes quiet, effective at all reasononable temp ranges likely to be encountered on the street, and reasonably priced. But under the high heat of repeated hard braking they can get hot enough to lose friction, and you may get "brake fade." So the 2nd step in improving braking performance is to get higher performing brake pads, realizing thet you may have to sacrifice some quietness and cold temperature operation. Many of us swear by after-market pads such as Hawk High Performance Street (HPS), which povide a bit of improvement in this area without sacrificing in any significant way on noise or cold temp operation.

3. Brake fluid. Also under repeated hard braking - like at the race track - the brakes may get hot enough to boil the brake fluid, also contributing to brake fade. So third step is to switch brake fluid to a high temp formulation. The downside to this is that high temp brake fluid is more hygroscopic than regular fluid, and consequently you must flush the brake fluid at least once per year. I woud recommend this only for the most aggressive canyon carvers.

4. Brake calipers. The last and least effective change to improve brake performance is to switch from the stock calipers to a multi-piston design, and also to consider a larger brake rotors and pads (a big brake kit). Larger rotors have more thermal mass, so can absorb more energy from braking with less temperature rise. Multi-piston designs can provide a more even clamping force of brake pad to rotor, and may give a better modulated feel in braking. This may be important at the track, where most braking is at threshhold level, but generally is not noticeable on the street. No one's running an X5 on a race track, so a BBK really doesn't do much for the X5.

So at the risk of sounding a little negative - there really is no practical reason to swap out the brakes from stock. Really the only reason to consider it is for the looks. Same reason why drilled or slotted rotors are so popular on sport cars and larger diameter wheel on all sorts of vehicles - it's the look! And yes, I admit - they M brake kit does look sharp!
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