High-Tech Braking Systems
The Latest Developments in What’s Stopping You!
h The disc brake as we know it was first patented in 1902, but it failed to gain acceptance in the U.S. until the early 1960s, when vacuum-assist power brakes made the pedal effort acceptable for the American driving public. European automakers had adopted disc brakes in the 1950s, rapidly following Jaguar’s dominance in the 1953 24 Hours of Le Mans race, thanks in no small part to the car’s four-wheel disc-brake system.
Disc-brake systems can be divided into two key components: the friction side, which is the hub/rotor and caliper clamping system, and the apply side, which includes the pedal, pushrod, booster (if any), master cylinder, and hydraulic lines. In more modern vehicles, a third system has been introduced: electro-mechanical controls like antilock braking systems (ABS). Originally, ABS was developed to rapidly modulate brake pressure to prevent locking up the brakes or tires, putting an end to uncontrolled skids. Relatively simple ABS systems have morphed into complex car-control and hydraulic-force application systems for elec-
tronic brake force distribution (EBD), such as anti-skid, stability control, and yaw control. By 2020, all new vehicles will have some form of automated emergency braking (AEB), along with a sensor, ECU, and algorithm-based predictive brake assist— and, yes, fully autonomous vehicles are coming soon.
One of the most interesting technologies on the horizon for enthusiasts will be integrated brake controls (IBC). An IBC uses a smaller, high-pressure pump that replaces vacuum pumps, vacuum boosters, or hydro-boost units. It is a compact unit that functions similarly to drive-by-wire throttles, weighing about 11 pounds less than the units it replaces. The control system will come from the OEs, much like GM and Ford crate engine/ trans combinations or the after- market’s adapted electronic-transmission controls like those from TCI, HP Tuners, FiTech, and Holley. This will allow enthusiasts to add ABS, stability control, and other similar features to their classic cars and rods with far less fabrication and hassle.
On the friction side, two major elements are driving the technology: 1) the need to absorb and dissipate more heat due to heavier, higher-horsepower cars and trucks, and 2) the need to reduce weight to improve suspension control, steering response, and fuel economy.
In both cases, technologies developed for racing are trickling down into the enthusiast’s budget. The first such technology was aluminum calipers, made possible by improved materials such as 6061 and
7075 aluminum alloy and, more recently, 2618 forgings—the same alloy used in racing pistons. The next technology wave was the multi-piston caliper, which allows for the use of larger, curved pads with more swept area. More pistons of graduated size allow for finetuning of brake pressure across the pad face. However, more pistons add cost and machining complexity. While 8- and even 12-piston calipers had been developed at one time for cost-is-no-object racing, 6-piston calipers remain the gold standard for high-end sports cars like Ferrari, Ford GT, and the ZR-1.
The other major friction-side development was bigger rotors enabled by bigger wheels. Much like using a 1/2-inch breaker bar instead of a 3/8-inch ratchet, a larger-diameter rotor provides greater mechanical advantage for the same pressure applied at the caliper. However, bigger rotors mean more weight, so two-piece rotors with aluminum hats have become the serious upgrade for hot rodders looking to offset the necessary increase in rotor mass. For relatively little money, a two-piece rotor with optimum materials will not only look great but can also remove as much as 8 pounds per wheel, which helps acceleration and braking. As wheels have grown, so have rotors—now up to 16 inches on many trucks,
SUVs, and high-end cars.
Large rotor diameters have brought about the next evolution: floating rotors.
As rotor diameter and thickness have increased to keep up with today’s faster and heavier cars, increased rotor mass has exacerbated the effects of differential rates of heat expansion. To allow for that, rotors—or more often the rotor hats—are now slotted to allow the materials to grow radially while still being safely retained to prevent or minimize side-to-side motion. For street use with acceptable noise levels (the two parts can rattle under some circumstances), two approaches have been used: T-shaped bobbins that lock the hat to the rotor and more complex CNC-shaped rotor stanchions typically combined with anti-rattle clips.
The T bobbin is more compact and simpler to produce, saving some cost and allowing for tighter fitments. The stanchion style, while substantially more expensive, is better for eliminating or reducing noise, and due to its increased size and flat versus round sides, it can support 1.125-inch-thick rotors in 15- and even 16-inchdiameter sizes. The stanchion style is used almost exclusively for carbon-ceramic brakes due to its greater surface and clamping area.
01] ZF TRW’s integrated brake control (IBC), introduced this year, replaces the electronic stability control system, vacuum/booster pump, and the associated cables, sensors, switches, electronic controllers, and vacuum pumps with a single unit. IBCs also provide faster response, particularly for automated emergency braking triggered by onboard proximity and radar sensors. That faster response can mean a reduction of 10 to 20 feet in overall stopping distance, often the difference between stopping just in time and a crash.02] This prototype 12-piston racing caliper was attempted in the late-1990s, but the complexity of six individual pads, guide rods, and tiny pistons overwhelmed the intended benefits. 03] These calipers illustrate the growth in size of brake calipers over the last 20 years. Caliper size can increase as wheel size increases, allowing for larger rotors, calipers, and greater swept area. These larger calipers also show how racing technology has improved the brakes available to the performance aftermarket, with graduated piston sizes and castellated (slotted) pistons, or as shown here second from top, two-piece pistons with crenelated (complex, FEA-designed) milled caps.
04] These OE and aftermarket pads illustrate the effect of larger caliper size and increased swept area over the past two decades. Pads can be identified and purchased by application and cross-referencing using the Friction Materials Standards Institute (FMSI) numbers. From bottom to top: The pad shape and size used in Baer and Wilwood compact four-piston calipers, FMSI 480, the then-revolutionary 1984 C4 Corvette PBR pad, FMSI 412, Gen 4 Camaro, FMSI 731, C6 Corvette, FMSI 1247, and an FMSI 1405 pad used in aftermarket racing and ultra-performance street calipers.
01] Here is a 2015-and-later Mustang GT Performance Pack rotor and a similarly sized, two-piece replacement rotor. The replacement two-piece rotor weighs 7.9 pounds less, which helps reduce stopping distance and lap times. It has curved vanes for better cooling and uses NAS S287 fasteners(see sidebar, above).02] On these 14-, 15-, and 16-inch rotors, we see the three types of two-piece rotor attachments: the fixed T-shaped bobbin and the stanchion-style bobbin.03] This two-piece, slotted rotor shows the T-style bobbin components used to fasten the hat to the rotor in lateral attachment; they still allow for differential growth due to heat in the radial dimension.04] The Corvette Z06/Z07 package’s carbon-ceramic brakes; note the floating rotor hardware and the small drilled holes. These holes are more for fashion than function.05] This stanchion-style bobbin shows the precisely machined dimensions, the 0.0001-inch tolerances, the anti-rattle retaining clips, and a plain rotor for this road-race-only application.