Buying a big brake kit? Read this first!

Let’s talk about big brake kits for a bit. For the purposes of this article, we’re going to refer to any upgrade in rotor diameter and caliper size as a “big brake kit” or BBK for short.

Not a week goes by that we don’t get a question on the forum (or on one of the many Facebook groups that I and my staff administer) from someone asking about installing a BBK on their car (or truck).

The quick and dirty answer is, in 90% of cases, you simply don’t need any such thing. I know, I know – that response ruffles the feathers of every fanboi who learned everything about cars from the Fast and Furious franchise, and their defensiveness comes spewing out like braps out of a fartcannon.

It usually sounds like this: “But my favorite car, the [insert supercar make and model here] has 15″ drilled and slotted discs and massive calipers.“

That’s neat, Scooter. You don’t own a Porsche 911 Turbo S, you drive a Civic. Or a BRZ. Or a Corolla. The point is, that car on the poster on your wall has those brakes for reasons, and those reasons don’t apply to you. We will, however, talk about factory BBK applications later, but let’s get the basics first.

The old rule of thumb is this (and it’s the same for older AND newer cars):

• If you can lock up the brakes on your car on dry, clean, flat pavement under a panic braking situation (and I’ll bet you can), then stopping distance will not improve (and may even get worse) with a BBK.

• If you can engage ABS on your car on dry, clean, flat pavement under a panic braking situation (and again, I’ll bet you can), then stopping distance will not improve (and may even get worse) with a BBK.

Obviously, both of these statements assume you don’t have other issues with your braking system, such as air in the lines, faulty ABS sensors, leaks, glazed pads, a bad master cylinder, a bad booster, or incorrect adjustment of pedal engagement. If any of those apply, you don’t have any business shopping for blingy parts, you need to make your brakes function the way they were designed. Stop reading now, and come back after you fix your brakes.

OK, but let’s say you have more mechanical aptitude than the average slobbering F&F fanboi. Maybe you’ve successfully passed a Physics class, and you’ve even got a few track events under your belt. Sweet!

You may have learned a term called “threshold braking,” and you may even think you’re skilled enough to always apply your brakes at the threshold of lockup (or ABS engagement). The problem here is this: That threshold that you learned about (defined as the razor-thin point between not breaking traction and breaking it) is not only unlikely to do you any good in a panic stop on the street, but more importantly, it’s not controlled by the brakes at all.

We learned in Physics that when attempting to stop the rotational motion of a spinning disc, we want to grip it at the outermost edge, and that a larger diameter disc will allow for more stopping power. This is based on the premise that, as you increase the size of the rotor, you are able to move the clamping force further from the center, and therefore you increase the leverage of the forces acting upon that rotor (in this case, the caliper and pads), making it easier to stop.

The missing piece of the puzzle here is this: Let’s assume the rotor can be stopped instantaneously, kind of like a bicyclist jamming a stick between their spokes. BAM! Assuming the rider is strapped to the bike, what happens next? You guessed it – a skid.

What this means is very simple, but can be incredibly difficult to grasp, especially for the uninitiated automotive enthusiast. The ultimate determinant of braking efficiency is NOT determined by your pads, calipers or rotors, but by your tires. Read that again, and commit it to memory. See, your brakes aren’t touching the ground. Your brakes simply slow or stop rotation of the wheels, so your braking force becomes irrelevant if there’s not enough friction between the tires and the road.

A higher coefficient of friction between your tires and the road equates to reduction in stopping distance. Let’s say that again, but more succinctly: Better tires reduce stopping distances significantly. The caliper and pads can clamp the rotor sufficiently to induce lockup – we’ve already established that. But the tires do the actual work of stopping the car – and if the tires don’t stick, you get skidding or ABS engagement, both of which are indicative of insufficient friction at the tire / surface interface, AND translate to you hitting something.

OK, so by now, you’re mad that we’ve scientifically debunked your plans for blingy drilled rotors and massive shiny calipers, and you’re looking for any excuse at all to spend that money on something more glamorous than sticky tires. All right, let’s discuss what a BBK does bring to the table – but don’t get too excited, because it STILL may not justify you dropping a fat wad of money.

1. Bigger brakes (larger rotors, larger pads, larger calipers) are better at resisting what is commonly called “brake fade.” Brake fade is a loss of braking effectiveness due to excessive temperature of one or more brake system components. I’ve heard drivers talk very convincingly about experiencing “brake fade” (usually when they’re explaining why they rear-ended another vehicle in traffic). They’re misusing that term, so don’t be one of them.
   
2. Bigger brakes heat up less and dissipate heat better. Let’s go back to our Physics lessons: A larger object has more surface area. As such, more surface area means better heat dissipation. For an equivalent stop, with all else being equal, larger brakes allow for more consistent stopping distances (and more consistent pedal feel) time after time under hard use, such as a track environment. But let’s go back to the beginning of the article, and remind you, you’re not driving a track car. This is your daily driver, and real-world brake usage is absolutely nothing like the usage that occurs on, say, a road course. One panic stop isn’t going to generate enough heat to matter.
   
3. Bigger brakes CAN increase clamping force AND do so further from the center of rotating mass. That’s all well and good, except some of that increased braking power is lost, because the brake system has to slow down more rotating mass, the larger, heavier brake discs. So, again, your net gain may be decreased or even nullified.

Now that we’ve crushed your hopes and dreams of “killing the game” with your flashy BBK purchase, we’re going to add salt in the wound. A BBK may actually increase your stopping distances, which is exactly what you were trying to avoid. Why is that?

Well, going back to our discussion of dissipating heat, we can’t assume that ALL heat is inherently bad. In fact, certain brake pad formulations are designed for optimal function ABOVE a given temperature. So, while your BBK is doing a great job dissipating heat, you’re asking the pads to do something they’re not designed for, which is to grip the rotor below their optimal temperature. Cold pads and rotors can, in some cases, be a bad thing. Oops. You just spent a lot of money to make it worse.

Also, a BBK is, by definition, larger. Larger rotors, larger pads, larger calipers. Everything is bigger. When everything is bigger, everything is heavier. Even the F&F crowd knows that you add speed by reducing weight, right? Well, that’s the simple explanation. But it gets more complicated. See, when it comes to where you want to reduce weight, there’s unsprung and sprung weight, defined as follows:

Sprung weight is everything supported by the springs.

Unsprung weight is everything else: Spindles, hubs, lugs, brakes, wheels, tires.

Decreasing the sprung weight of a car helps your power to weight ratio. That’s why we don’t put a massive audio system in a track car. That’s why we take out our spare tire when we go to the drag strip. Even the most amateur of enthusiasts can agree that reducing the weight of your car makes it accelerate better, handle better, and stop quicker. Science!

Similarly, lower unsprung weight (lighter wheels, tires, rotors, and suspension components) is even more beneficial to increasing performance. This is why automakers are utilizing aluminum extensively in suspension components (even on pedestrian vehicles like a Corolla). Under optimal conditions (think motorsports), every pound of unsprung mass removed is functionally equivalent to roughly 20lbs of sprung weight reduction. For a daily driver or enthusiast street vehicle, this ratio is nearer to 10lbs. But the bottom line is this: Unsprung and rotational weight should be your top priority in weight reduction for better overall performance.

Here’s yet ANOTHER way that BBK can actually work against you, if your goal is to reduce stopping distance. We talked about heavier weight being harder to move. That’s a constant, no matter if we’re discussing sprung or unsprung weight. Less unsprung weight means means better damping control. In other words, the suspension can react faster to driver inputs, as well as changes in road conditions. As an example of this, think about the fastest, most agile animals on Earth – they have small, thin, lightweight legs. They can move them faster. Less unsprung weight means initial turn-in is better, as is steering response and even ride quality.

Conversely, with greater unsprung weight (heavier wheels, tires, rotors, calipers, etc.), when you encounter road surface imperfections (bumps), the unsprung weight will be more difficult to move. This means that more of the bump force will be transferred into the car body instead of being absorbed by the suspension. So the takeaway from this is that increasing unsprung weight makes the ride bumpier, which in turn decreases a tire’s contact patch, and thus grip. THAT has a negative effect on traction – if your tires aren’t planted, they’re not helping your brakes stop the car.

But what about those cars that have a BBK from the factory? I promised you we’d address that, and that one’s easy to answer. The suspension geometry, unsprung weight, and even aerodynamic downforce has been carefully engineered to make that high-performance car perform impeccably with the components they’ve selected. They’re dealing with far more horsepower, far more demanding conditions, and far less margin for error. So, when you see a CTS-V or a GT-R or a 911 GT2 with massive brakes, remember that those components are lighter than what you can buy off the shelf, and they’re designed to make THAT car perform to the level that their owners demand (and, those cars are capable of speeds that far exceed your daily driver, so it keeps the attorneys happy).

OK, so let’s give you BBK fanatics a brake (break?)… Let’s assume you’re thinking, “But I saved up $1300 for drilled slotted 15-inch rotors and calipers that wrap 2/3 of the way around them, and I can’t wait to show them off at the next Cars & Coffee, dammit!“

So what do you do with all this extra money you saved by not buying a BBK? Well, you could go buy some shiny plastic faux caliper covers, but then the rest of us will just point and laugh – might as well leave your lip spoiler protectors on your Challenger.

In all seriousness, I promise you’ll wind up spending most (if not all) of that money on something that might not get you fanboi points, but WILL improve your car’s braking, handling, acceleration, and even comfort. Five easy steps:

Tires: Sticky tires is the single-most important modification you can do to decrease your braking distances. Period. Now, if you live in a place where mud and snow (M&S) tires or all-season tires are commonly needed, this can be more difficult. But, the idea is to look at the treadwear and traction numbers. In fact, most legit tire sellers like TireRack have these specs right on their website, AND some great educational material to help you understand what all the numbers mean. For example, I’m running a set of Hankook Ventus R-S4 tires on my daily. They’re a 200 treadwear tire (which means they WILL wear faster) and have a Traction: AA rating. In comparison, the Bridgestone Driveguard Plus in the same size has a treadwear rating of 640 (which means it’s harder) and a Traction: A rating. You don’t need my help to tell you which one will stop quicker, and I’ll gladly replace my tires every three years instead of six if it means I can avoid an accident.

Brake pads: Changing your factory brake pads to a set of performance brake pads will give a huge increase in braking performance. See, factory pads are designed to be cheap, quiet, and make minimal dust. But a cheap, quiet and clean pad isn’t helping you stop faster. Plan on washing your wheels more often, and opt for a more aggressive pad compound. This varies across brands, but depending on what you drive, there are great pads on the market from several manufacturers. I am a huge fan of the DS2500 line from Ferodo, but Hawk also makes some great aggressive street pads that can handle occasional track duty.

Brake fluid: Good brake fluid will massively improve the stamina of the factory brake system. Most people never even flush their fluid, and that’s a problem. Your brake fluid should be almost clear in color. The darkness is typically from two things: Deterioration of the inside of the rubber brake hoses leaves black particles in the fluid, and absorption of water (humidity) creates corrosion inside the metal lines of your system, coloring the fluid a rust color. Regular flushes are critical to keeping your ABS system happy and preventing expensive repairs. A higher-performance brake fluid can better resist boiling (see ‘brake fade’ above) but can also resist water absorption and maintain a consistent pedal feel.

Stainless lines: While you’re flushing your fluid and replacing pads, swap out those rubber lines on each corner for a set of braided stainless lines. They’re not expensive, they don’t need to be replaced, they’re not susceptible to deterioration or damage from road debris, and the best part is they don’t expand. During heavy braking, your rubber lines expand – they’re dealing with a LOT of pressure. Braided stainless lines provide a more consistent braking feel, and all of your “foot on the pedal” force is going into the caliper, rather than ballooning your soft rubber hoses.

Last step: Find someone who drives competitively on the weekends. Folks that run autocross or road course events are always glad to share what they’ve learned. Ask them about their braking setup… Even the guys with 90-hp NA Miatas put a TON of thought into their braking, so don’t be afraid to ask questions.

I hope this was helpful, and I hope it encourages you to look past the marketing hype and do your own research on the topic. Enjoy, and be safe out there.