Big Brake kit.

[Clark Kent]

This discussion will probably go down the same path as the steering damper threads. A lot of argument about benefits but ultimately a personal decision.

The point about stopping distance I make and Powerbrake claim is one of before and after upgrade. That's on a heavily loaded vehicle or towing when the factory brakes are working hard. For all the reasons stated a BBK should hold up better in those conditions by being less affected by heat due to improved dissipation. That translates to better comparable stopping distances by virtue of having less or no fade at the bottom of a long downhill (versus factory brakes). I'm talking of course about the useful ability to still have enough brakes left to be able stop at the bottom of the hill. Not the 60 to 0 style minimum stopping distance figures that auto review websites like to quote.

My input is about the lack of objective data from the manufacturers but I'm from an engineering background so that's a given. It's not hard to stick a deceleration meter on the windscreen and get some numbers and run some temperature tests as well. Alcon and Powerbrake must have done those tests as part of their own validation. But none of that matters. If you like what you're hearing here and elsewhere then go for it

 

[C-Mack]

In terms of an outright reduction in braking distance I doubt a Big Brake kit is going to offer much of a difference. The entire hydraulic system is designed to generate the same amount of pressure and move the same volume of fluid regardless of the caliper type hanging off the end of the circuit. To increase pressure and volume would require a redesigned master cylinder and all associated plumbing and valving.

Stock system is more than capable of locking up the wheels at any point so the tires coefficient of friction with the road is the ultimate determinant of stopping distance. Now in terms of heat dissipation the thermal mass a big brake kit should offer some benefit. Take two Grenadiers loaded to max and perform 10 repeated stops from 60 mph and in theory the vehicle with the bigger brakes should experience less overall brake fade.

With regard to initial brake bite the larger diameter rotors offer more leverage but only up until the point of tire lockup but feel and modulation might be improved giving the sense of higher performance or more stopping power. But this brings up a larger point about how subjective all of this can be. Like most aftermarket products they are engineered to fit a specific application and may be tested on a sample vehicle for functionality. Most engineering work would have been done on a brake dynamometer in a controlled environment to generate base performance numbers not out in the wild in various weather conditions, vehicle weights, terrain types, towing, driving styles, long term durability, etc…

Big brake kits aren’t going to stop your Grenadier like an F1 car or produce enough braking force to stop the world from rotating but should offer better heat management and less fade during repeated and prolonged use such as on steep grades or with a heavily loaded setup where any increase in safety margins would be welcome.

 

[parb]

That is my use case, heavily loaded and driving on mountains and climbs.

 

[AWo]

That all is physics, proven physics and no one can evade physics. Just have a look at racing. They use larger break surfaces solely for heat dissipation. That of course leads to better braking in terms of you can longer use the standard brake power. For braking force they change the brake disc to carbon or ceramics and other very expensive stuff because its friction coefficient is much higher that steel (and they cope better with heat).

It all may look complicated, but it isn't.

With a smaller brake pad the pressure applied to the brake pad is higher, but the surface which acts is smaller. By changing to bigger pads the pressure per square mm is reduced, but the the surface areas is larger. That equals out.

That is also expressed in the formula for friction:
Friction FR = friction coefficient of the material μ x Pressure N - there is nothing about the surface area size.

Now let's check how braking power is calculated:
Let's start at the main braking cylinder. The driver pushes the pedal and generates Force F onto the surface of the main brake cylinder piston A. This force is applied to the brake fluid:

Brake Fluid Pressure P = Pressure Power F / Surface Area of the main cylinder piston.

At the wheels Pressure P presses onto (larger) pistons therby multiplying the force:
Brake Force F = Brake Fluid Pressure P x Brake Piston Surface A

Let's take some real world numbers. Strong braking can generate 180 bar of pressure. We have a wheel braking piston surface of 40 mm2 and 22 mm2 at the main braking cylinder piston.

180 bar = 3,960 N / 22 mm2 at the main brake cylinder (3,960 N is the power pushing onto the piston, so the power the driver applies and the leverage which is applied, typically 4:1 or 6:1).

As the brake fluid pressure is the same everywhere in the system the brake cylinder pistons at the wheels are the factor which makes up the braking force:

7,200 bar = 180 bar x 45 mm2 at the wheel brake piston.

Change the piston sizes and you got it.

Nothing to argue here. Physics don't care about arguments. Or simply try to get hold on someone who is in this business and have a chat.....

AWo