How to design a BBK for any car

So you want to design a BBK (big brake kit) for your own car. It could be a street, race, rally or any other motorsport discipline car. In this post I´ll be going through more of the design aspects for street car, but there will be one focused more heavily on race cars later.

Big brake kit usually just called BBK for short is a "kit" that consists of the following parts to allow you to run larger brakes.

BBK consists of:

• Larger diameter brake discs.
• Either larger one piston brake calipers or multiple piston calipers.
• Adapter brackets to adapt the new calipers to your vehicle.
• Not all kits, but suitable brake lines for this conversion.

Now that you know what you need for your BBK to work. Next up there is some design aspects that need to be taken in to account.

Most important one being what is the law in your country? Can you run custom brake kits on the street or do they need to have for example TUV certification. If this is the case then just buy a BBK from big company. As this would get really pricey for just one set of brakes.

If you are free to modify your brakes then next question is the packaging of the brakes. How much room you have to work with? What type of wheels will you be running? Which ET? How much back spacing the wheels have behind the wheel spokes?

These are all questions you need to have answers for before designing, or just design the brakes and find wheels that will fit around your brakes.

When it comes to the brake calipers you will have few options regarding this upgrade. First option that is the most budget friendly is to look for 1-piston calipers. These can often be found with bigger piston diameter with even matching carrier bolt pattern making adapters obsolete. Then just give them some better brake pads and you are ready.

A "true" BBK usually has either 4-pot or 6-pot brake calipers. Meaning the brake calipers have 4 pistons, 2 pistons on each side of the caliper or in 6-pot they will be having 3 on each side. These calipers can be found on some of the heavier cars or with higher power levels such as M-cars, AMG, RS, etc. Or on vans, pickups like Hilux.

Depending on what brake calipers you land on. Next is to check which type of mounting they have. 1-piston calipers are always mounted with carrier that allows the caliper slide freely. Giving the affect of having piston on both sides. Some 2-piston calipers are also carrier mounted when the pistons are on same side. These are particularly common on heavy vans.

Calipers with opposing pistons. Have two common types of attachment. They can be either radial or axial mounted. Brake calipers found on production cars more often have axial mounts even on the multiple piston calipers. This can be beneficial when designing the adapters, but it can also make the design more complex. Depending on the size of the brake disc and location of the original brake caliper.

Now you have your brake calipers that you would like to be using. Next up is to figure out what size of brake disc is designed for them. This is usually easy to find out. Specially if you have the part number for the calipers. Find out the disc size and thickness. Both measurements usually have little bit of flexibility. For example you could raise disc size from OE 300mm to 330mm usually with out much of a penalty. Or if the thickness of OE is 30mm you could use 28mm thick disc, but not 32mm with out having to modify the brake pads (remove material).

Have found the size of the brake disc that you would want to use? Let´s for this example go with 340x28mm brake disc. You have calipers that fit this disc size properly and pads that require no extra work. If you are working with budget try to find discs that have correct offset, bolt pattern and centering hole. If these can´t be found there are two options. One is to get a disc with correct offset and have a machine shop machine the disc to fit your application. When taking this approach make sure the disc has smaller centering hole than what you need. Bolt pattern can usually be easily adapter with out risk of weakening the face of the disc.

Other option is a step away from 1-piece discs and go for 2-piece. This means you would have removable disc part and "top hat" part that bolts to your wheel hub with correct offset. These are relatively easy to design and manufacture even by yourself. Just use good quality aluminium and wall thickness of around 6mm. On cars that rarely see any track use I wouldn´t see point in going for floating 2-piece construction as they tend to be noisy, but if your car is track day weapon then why not.

Now you have your caliper and disc combo that you can almost "bolt-in". Next up is the design of the adapters that will tie this combo in to a working brake setup. You have to determine where your caliper needs to sit in correlation to the disc. Then measure the differences between the mounting locations and sketch out a adapter to fill this gap. Take note of the mounting style of the caliper. Does your caliper has through hole or threads? Do you need to offset the caliper from the original mounting location?

For material use good quality aluminium or steel. When using aluminium think about how you will be changing your pads. If pad replacement requires removing of the caliper maybe use steel threads like helicoil, to prolong the life of the threads. Also keep in mind how you will install the brake kit. Do you need access to the mounting bolts in which order?.

Often when changing brake calipers. You will need to also change your brake lines. This change should be taken account when designing. What type of connector does the new caliper have? Is it a banjo bolt while original was something else? Also you might need longer lines. Often custom lines are needed or connector adapter. Try to avoid using adapter in your brake lines as they only make more points of possible failure.

When going to custom brake lines. I would recommend going straight to steel braided lines as they give better brake feel and don´t swell even when exposed to extreme heat.

What else you will need for your brake kit? What mounting hardware will you use? If the calipers are radial mounted. Make sure your mounting bolts clear your wheels inner diameter. Use bolt with proper grade (recommended grade 12.9)! Also use loctite on the adapter bolts and/or safety wire.