Junkyard Caliper Upgrades a good idea?
Mark Valskis from Brembo North America helps explain what goes into a properly designed big brake system. Upgrading the brakes on Honda Civics to Type-R calipers and rotors or bolting up the bigger 300ZX brakes to S13s and S14s are classic examples of upgrade paths that have proven to be both affordable and effective for grassroots enthusiasts. But more recently I’ve noticed a trend where some hard parking import enthusiasts are bolting huge multi-piston calipers and rotors off of European exotics like Porsches and Ferraris to their Subarus, Mitsubishis, Hondas and Nissans. This may look cool in the coffee shop parking lot, but as I learned when upgrading to the 1-inch Type-R master cylinder from the original 13/16-inch CX model master cylinder on my EG race car (which made a huge difference in brake pedal feel and firmness), there’s a lot more to properly upsizing your braking system than just adding larger-diameter rotors and increasing the number of piston in your calipers. According to Mark Valskis, engineering manager at Brembo North America, The first thing to consider in regards to the brake system is safety. There is a very large misconception that any caliper can be used on any vehicle, as long as it can be made to physically bolt up in some manner. However, there are vast differences in braking systems between vehicles, and often in ways that would not be predicted. For example, a Subaru WRX has approximately 30 percent more brake piston area than a Porsche 911. Taking a caliper from that Porsche application and applying it to a WRX (all other things being equal) would result in a 30 percent reduction in braking torque and a significant (and very unsafe) shift of brake balance to the rear of the vehicle. Understanding the importance of rotor thickness, not just diameter, and how this can impact performance and safety is also a key element to factor in when doing any sort of custom retrofitting of brake parts not designed for your car. A fundamental consideration is the brake disc thickness, Mark says. In a great many cases, we see calipers being used on discs that are thinner than what they have been designed for. In these cases, once the pads and the disc have worn, the first thing that can happen is the brake pads move past the abutment surfaces on the caliper, resulting in damage or brake failure. It is also possible that the pistons move completely past the seals in the caliper, resulting in complete and catastrophic brake failure. Just like the rotors, the calipers are also designed for specific operating conditions, so bolting them up to an entirely different chassis can also be problematic, if not downright dangerous. The caliper bodies themselves are built to withstand the structural requirements of their intended application, Mark says. We have seen instances where calipers are being used far outside the bounds of their design loads. The ABS system is also designed to function optimally only within the parameters of the original braking system.
By using components that are well outside these bounds, especially as it relates to fluid volume which is impacted by caliper piston area, caliper stiffness and so on the ABS system performance suffers. Mark also made the excellent point that custom retrofits, like we’re starting to see more of, also involve producing a caliper bracket adapter, a component that needs to be designed, analyzed and tested to prove its integrity for the system’s lifetime. Mark elaborates, Even if the components chosen to adapt are appropriate, without this very important detail being properly designed, the system could also be extremely unsafe and experience a catastrophic failure. The primary benefit of upgrading to bigger brakes is, of course, greater fade resistance and improved modulation, rather than one-stop braking distance. As we experienced firsthand with Project G35, where the undersized (non-Brembo) OEM brakes were quickly overwhelmed by the heat buildup produced by track testing, only when we upgraded to significantly larger brakes (in this case AP Racing front and rear BBKs) did we see consistent braking performance lap after lap. The BBKs provided the ability to efficiently convert, store and dissipate the kinetic energy (in the form of heat) being produced during repeated and heavy deceleration. As to the question, How big is too big? when it comes to upgrading a braking system for high-performance use, Mark from Brembo responded, While mass in the brake disc is generally beneficial to the performance of the braking system, clearly it is not to the other performance parameters of the vehicle, such as acceleration, ride and handling due to the effects of increased unsprung mass. The brake disc mass must therefore be properly balanced with other performance considerations. In many cases, depending on the vehicle in question, it’s possible to reduce the system’s overall weight while increasing the thermal capacity of the brake disc. This is possible due to multi-piece brake discs and high-performance, fixed-mount aluminum calipers in place of factory one-piece discs and cast-iron sliding calipers.
Mark then expanded on the topic of brake system sizing by adding, First, we should dispel the myth that more equals better as it relates to components of the brake system, calipers in particular. Simply increasing the number of pistons in a caliper does not make for a superior caliper. The number of pistons in a caliper is a function of optimization for a particular pad shape and piston area, and for the most part, has little direct bearing on the performance of the braking system. Likewise, increasing the piston area is not the mark of a superior brake system. We often see ads or statements expounding upon X percent’ increase in piston area or braking power. The fact is that in almost every circumstance, this is to be specifically avoided. Given that Brembo is the global leader in braking system design, a fact proven by its dominance at the highest levels of motorsport, as well as being the factory choice on many of today’s highest performing road cars, we asked Mark for a little insight into how the company goes about designing its BBKs.
The design of a Brembo GT braking system first begins by an analysis of the original equipment braking system and the pertinent vehicle parameters. This includes the dimensions of all of the original braking system components, including piston area, pad area, disc diameter, thickness, annulus width and air gap. The most pertinent vehicle parameters are the gross weight, weight distribution, center of gravity, wheelbase, top speed and vehicle usage, as well as tire size(s). Calculations are then performed in order to determine the best disc size for the application. Brembo has internal standards for this, based on our experience as an OEM supplier, the performance aftermarket and top-level racing. Due to our unique position in this respect, we have performed tens of thousands of road, track and dyno tests on vehicles and have used this data to establish a threshold for the disc thermal capacity. The caliper piston area is selected in order to closely maintain the original braking torque and fluid volumes. Calculations and dynamic simulations are performed to verify optimum brake balance through the full range of deceleration rates and to ensure safety, performance and the integrity of the ABS system. Further calculations are made for the brake pad surface area and volume. Mark then went on to add that, Each of Brembo’s calipers undergo complete functional and structural testing, as well as environmental testing (salt spray corrosion, etc.) to prove its strength and fatigue lifetime. These tests have been performed at values exceeding that of any application that it is to be employed in. Each time a new application is created, the loads are compared to the qualification values to verify that the caliper meets the structural requirements. If an application should happen to exceed the tested parameters, a full complement of structural and fatigue testing is performed at new higher values. Discs have likewise undergone full dyno testing for thermal shock, thermal fatigue, high deceleration resistance, friction coefficient, wear, etc. The disc bells and caliper brackets are designed to adapt the Brembo disc and caliper to the vehicle. Using the results from the braking system calculations as inputs, these components are analyzed using finite element analysis to evaluate the stress levels, and are physically tested to verify fatigue life at maximum applied torque. There is, of course, a lot of very interesting science and engineering hidden beneath the surface of a high-quality BBK, things like material choices and design considerations that maximize caliper stiffness. Look for a future discussion on this very subject, if we’re fortunate enough to tap into the bottomless pool of brake system knowledge housed by Mark and his team of engineers at Brembo.