Your Big Brake Kit and You
Big brake kits are a great way to improve reliability, driver confidence and time on track while also reducing consumable cost (sometimes). In a previous article we talked about the different components of braking systems and various upgrades, the purpose of this article is go to into some of the science behind braking to help understand what to look for when shopping for a big brake kit.
Before I talk about what big brake kits are intended to do, we're going to cover what they don't do. There is a misperception that big brake kits will inherently stop a vehicle in a shorter distance. This is NOT what big brake kits are for nor do they accomplish this in most cases, big brake kits are made to be able to handle the increased heat and wear that comes from repeated heavy brake use. Stopping distance is mainly a function of friction between the brake pad and rotor, and of course the tire's ability to maintain traction under braking. If you wanted to decrease the stopping distance of your vehicle in an emergency braking situation this can be achieved with just a change in brake pads, but bolting up a big brake kit with a similar pad as what's already on your car will not make it stop faster. So with that out of the way, let's get into what they we want to evaluate when considering a big brake kit.
Thermal Mass - Thermal mass is a key metric when talking big brake kits. If the brake system can't absorb more thermal energy, then it's not really a big brake kit! In some cases there are common upgrades to use brakes from another vehicle as a means of a "big brake kit", like is popular with TL Type S Brembos on many Hondas, but the rotor that gets used isn't any larger or is even smaller than the original rotor in some cases. This type of upgrade does help with better pad wear due to a fixed vs floating caliper, but it does not increase thermal mass of the brake system.
The rotor is responsible for absorbing the majority of the heat generated in braking, so in order for the rotor to be able to handle more heat, the size (either diameter or thickness) needs to be increased. In my opinion, the best way to increase thermal mass is through increasing rotor thickness because increases diameter will change braking bias (which is our next subject) and also may require an increase in wheel diameter to accommodate. How much more thermal mass you need entirely depends on how hot your existing brake components are getting, this can easily be determined with special temperature stickers on the calipers and temperature paint on the rotors.
Braking Bias - One of the most important yet least disclosed details on big brake kits is how much they affect braking bias. Simply put, brake bias is how much force is transmitted to the front axle versus how much goes to the rear axle when the brakes are applied.
This is important because it will affect how the car behaves under braking, most notably which axle will lock up first under heaving braking. Bias can be altered by changing a few variables which affect the resulting braking force at one axle. These variables are caliper piston area, (effective) rotor diameter, and brake pad compound.
With most big brake kits, caliper piston area and rotor diameter are different than the factory caliper and rotor, so these need to be balanced appropriately in order to keep from bias being changed too much from the factory bias. The main reason you want to keep bias relatively close to factory bias is because of the anti-lock braking system (ABS), which is a computer system that controls brake fluid pressure going to each wheel in order to reduce the chances of a wheel locking up under braking. This computer is calibrated for factory bias, so changing bias too much can cause undesirable results from the ABS module.
4 vs 6 Piston Calipers - Something that often gets misconstrued is that higher piston count is synonymous with more braking force, and thus a better braking system, but in some cases a 6 piston caliper offers no benefit over a 4 piston caliper. The purpose of multi piston calipers is to apply more even pressure across the length of the brake pad. Whether a 4 piston caliper is adequate or 6 piston caliper is more fitting depends on the length of the brake pad. Brake pad length is tied to pad shape which will depend on the caliper being used and often goes hand in hand with rotor diameter.
My rule of thumb is that a 4 piston caliper is plenty sufficient for rotor diameters up to 340mm and any rotor that's 350mm or larger is best suited with a 6 piston caliper. Using a 6 piston caliper on a rotor smaller than 350mm means adding unnecessary unsprung weight onto the car as well as more points for failures or leaks, and using a 4 piston caliper on a rotor larger than 340mm increases the likelihood for uneven pad wear.
Brake Pad Area - There are many many different brake pad shapes on the market. In some cases with aftermarket calipers there are multiple shape options that can be used, usually because there are various annulus height options. The main takeaway from pad area as far as performance is concerned is that the larger the pad area is the longer life the pad will have. This is due to the braking force being distributed over a larger area, which results in slower wear.
Floating vs Non Floating Rotors - This is something not talked about too often but it is very important for getting good even brake wear on track. There are two ways to construct a 2 piece rotor, floating and non floating. With non floating rotors the friction ring is bolted straight to the center hat, and outside of being lighter it performs very similarly to a 1 piece rotor. With a floating rotor the friction ring is located to the center hat with small inserts called bobbins. The bobbins allow for some play between the center hat and friction ring, this allows the rotor to expand more evenly as it sees the extreme temperatures found on track. 1 piece rotors and fixed 2 piece rotors are much more likely to have uneven brake pad wear with track use because they can't expand uniformly like a floating 2 piece rotor can. Another advantage is they are less likely to cause pad knockback issues compared to fixed rotors. The downside to floating rotors is they make a lot of small clicking noises when the brakes aren't hot so they are not a great option for a daily driven car.
Straight vs Directional Vane Rotors - All big brake kits come with vented rotors. What this means is the center of the rotor allows air to pass through it, this greatly increases the rotor's ability to shed heat compared to a solid rotor. But not all vented rotors are created equal, the size of the air gap greatly affects how much air can pass through the inside of the rotor and an even more important factor is how the center in constructed. For the rotor to remain strong and handle braking pressures there has to be structure in the center of the rotor and this come in the form of vanes. Straight vanes are typically what is used in factory rotors and the one upside to them is that they can be used on either side of the vehicle. Directional vanes are better though. While they are side specific, when the vanes are angled, it turns the rotor into a more efficient air pump and the amount of air that passes through the rotor goes up considerably. This is made even greater when the directional vanes are curved too!
Consumables - Consumables are an often overlooked aspect of big brake kits but it's one of the most important in my opinion. Consumables for brakes typically means brake pads and rotors. Nearly all aftermarket calipers used in big brake kits will use pad shapes that are not found in OEM applications, which is neither good or bad, just something to be aware of. With the majority of aftermarket big brake kits a non factory sized rotor is used, this means you may only have one or a few sources to get replacement rotors, and that can mean at a higher price, but ideally it also means you don't need to replace rotors as often because the larger rotor should live a longer life than the factory sized rotor.
Wheel Clearance - Wheel clearance is a huge factor for many people when shopping brake kits because nothing makes for a worse feeling than dropping thousands of dollars on brakes only to find out that your wheels no longer fit. Most big brake kits are considerably worse on wheel clearance than factory sliding calipers because fitting a second set of pistons on the outboard side take up a bunch more space, it's just the nature of the beast. I included this section because it's something to be aware of when you're shopping for brakes and ideally the company selling the brakes has a fitment template you can print off and cut out to check with your wheels before you buy so you can make sure you know what you're getting into prior to installing a big brake kit.
Dust Boots - Or lack thereof. Dust boots are a standard components on all OEM calipers, but are rarely found in aftermarket big brake kits. The reason for this is dust boots can't handle long term exposure to the ambient heat that brakes generate on track and they crumble away. If you're using your car for a lot of street driving and it's not a dedicated track car, having dust boots will help the piston seals live a longer life. This is one of the main reason we use EBC calipers in our brake upgrades, it allows us to offer a street caliper that uses dust boots and is still capable of moderate track use, as well as a track version which doesn't use dust boots. For those that feel a caliper with dust boots makes the most sense for their uses, titanium pad shims do a good job to help extend dust boot life if being exposed to high heat like on track.
Piston Material - Piston material is a big factor in how well a caliper will resist heat transfer into the brake fluid, the three most used materials for pistons are aluminum, stainless steel, and titanium. Most OEM fixed calipers utilize aluminum pistons, as do many aftermarket calipers in big brake kits. Aluminum pistons are preferred for street cars that see year round use because they have the same thermal expansion as the caliper body. Where aluminum pistons fall short is on track, because aluminum transfers heat really well it doesn't do a great job of keeping brake heat from getting to the brake fluid and boiling it. Combining high brake temps with repeated high pressure stopping (like on track) can also cause aluminum pistons to soften and deform if the piston isn't thick enough. If the deformation is serious enough it can cause seals to wear out prematurely or fail.
This is why stainless steel is often utilized on more track focused calipers. Stainless steel does a much better job of insulating the brake fluid from brake heat. It also doesn't soften when exposed to high temperatures found in brakes, but because it doesn't shrink at the same rate as the caliper it is possible to have piston binding issues if the car is driven in extreme cold temperatures which can wear out seals, pistons and caliper bodies in the worst case. Stainless is also a good bit heavier than aluminum so the caliper weight goes up with stainless pistons. The street version of EBC calipers use aluminum pistons, and the track version use stainless steel pistons.
The last material used for pistons is titanium, it is the best choice for brakes used on track as titanium transfers heat even less than stainless steel, doesn't soften when taken to high temperatures like aluminum, yet isn't much heavier than aluminum. The major downside of titanium is its substantially higher price, which is why it is only really utilized in very high end racing calipers, but I felt it was worth mentioning here.
And that bring us to the end, hopefully this helps you figure out what option on the market makes the most sense for you when you're shopping for your next big brake kit. If you have any follow up questions to anything you read here leave us a comment below or shoot me an email at austin@wunderladenracing.com. If you're looking for a big brake kit for your 8/9/10/11th gen Honda Civic we offer our own brake kit that offers unparalleled versatility, and for our Evo customers we have something in the works for you too! Thanks for reading along, stay tuned for our next blog post!
- Austin and the Wunderladen Racing team