Breaking Braking Myths: A In-Depth Guide on All Things Brakes

By Garrett Davis - April 30, 2020

There’s a right way and a wrong way to do anything, and through the fog of relentless marketing hype, that line can get a little hazy. Every brake pad, rotor, and kit says that they’re the best, and that they’re an upgrade from whatever you already have. However this is the real world, and not everyone gets a first place trophy. Brake rotors, and pads are not a one size fits all kind of part. What works for a soccer mom isn’t going to cut it for someone’s truck brakes towing a boat or doing weekend track days.

Braking system overview

TL;DR: On the simplest level, your brakes work by using hydraulic force to press a fixed friction pad (brake pad) against a rotating assembly (brake rotor or drum), converting kinetic energy into heat through friction. This slows that rotating assembly to a stop, and with it, you and your vehicle.

Going deeper

Being a hydraulic system, your car’s brakes take advantage of Pascal’s law of fluid dynamics as its means of force amplification. Pascal’s law basically states that any pressure change enacted on an incompressible fluid will be transmitted equally throughout the fluid in every direction. That makes sense, right? But how do we use this principle to our advantage in a brake kit?

In the diagram above, basically what we have is a U-shaped tube with a piston on each side. The tube is filled airtight with incompressible fluid, so any pressure applied to the one side will be transmitted through the fluid to push the piston on the other side. By making the surface area of the right piston 10 times the surface area of the left piston, 10 times the force will be transmitted to the right piston. 100 pounds of downwards force on the left piston results in 1000 pounds of upwards force on the right.

So to apply this concept for use in vehicle braking (generally speaking), we apply that pressure via the brake pedal as it pushes against smaller surface area pistons in the master cylinder, through the brake lines to the pistons in the calipers, which collectively make up the larger surface area side of the equation.

There are also a few other tricks manufacturers use to give the driver a mechanical advantage. For instance, the brake pedal itself is on a lever arm to multiply the force applied to it similar to how a breaker bar gives you an advantage on tough bolts. Most car or truck brakes these days will have a pedal ratio between 3.2:1 and 4:1. In practical terms, this means that 70 pounds of force on the brake pedal from the driver will translate to 224 or 280 pounds respectively.

After that, manufacturers use brake boosters to give drivers a further advantage. Brake boosters work by pulling vacuum from the engine as an assist in pushing a large diaphragm before the master cylinder, which then in turn pushes the brake fluid out to the calipers. A 7" diameter with -8 PSI of vacuum from the engine will result in over 300 added pounds of pressure going into the master cylinder.

The result of adding these systems together results in thousands of pounds of clamping force at the calipers. So much so that anti-lock brakes became an invention of necessity in order to prevent complete lock-up of the wheels, resulting in loss of control of the vehicle.

Brake Pads and Rotors

Now that we’ve established a general idea of how your brakes work, let’s take a look at the components you’ll be dealing with the most: Your brake pads and rotors.

Your brakes work by way of two forms of friction – abrasive and adherent:

Abrasive friction: When the pads are pressed against the spinning rotor or drum, the crystalline structure of the pad material and even the cast iron disc break down, converting kinetic energy into heat, bringing the disc (hopefully) to a stop. Being that the brake pad is the softer of the two materials, this wears down the pads more quickly than it wears down the rotors.

Adherent friction: As pressure is applied to squeeze the pad to the rotor, some of the pad material breaks apart and reforms, bonding to the surface of the rotor. This process saps energy away from the turning of the disc, spending it to create that bond (along with as heat). This is the method of friction that is used to bed your pads to the rotor.

All modern brake pads use both types of friction, just to varying degrees depending on the application. Semi-metallic pads lean more towards abrasive friction, and therefore are tougher on rotors and create more dust in a trade-off that results in the ability to operate effectively at temperatures. Organic and ceramic pads lean more on the side of adherent friction, the trade-off being that they’re easier on rotors, have better cold performance, and are quieter, though sometimes that is at the cost of high-temperature performance (depending on the formula).

In order to ensure normal, and even brake wear between your pads an rotors, manufacturers recommend performing the process of bedding in your brakes.

This is a process to “mate” your pads to your rotors with gradually increased heat cycles to create a thin, even film of brake pad material on the surface of your rotor. If the rotors and pads are not properly mated with each other, you could end up with brake shudder, squealing brakes, and uneven wear.

How does bedding in your pads pertain to the brake judder you’re feeling in your brakes?

If your rotors have not been bedded-in properly, or they were pushed too hard and lost that bedding, you can end up with uneven pad deposits on the surface of the rotor. At first, this just means uneven grip across the surface, causing the pads to grip, then slip, then grip, then slip, etc, and that’s an early stage of the judder you’re feeling as you brake. At the extremes, if this is not corrected, this can result in uneven rotor wear, and ultimately a “warped” rotor. I use quotes there because the term is a bit of a misnomer (more on that later).

Why are my new brakes squealing?

There tends to be a lot of confusion here due to the fact that most brake pads come with a metal tab that will sound against the surface of your rotor to indicate that your brake pads have worn down to a certain point. So now when most people hear their brakes squeal, they think that they already need to be replaced, but that is often not the case.

What’s happening here is that the conditions are just right for your rotors to vibrate as they pass through the clamping pads, not unlike how a bow being dragged across the strings of a violin work — the main difference being that a violin is a lovely sounding instrument in the right hands, while a squealing brake rotor tends to scream in the key of “ouch.” Not pleasant.

Proper bedding of your rotors can go a long way in reducing this effect, but there are a few other factors that can contribute here. For instance, a layer of rust on your hubs when you install your brake rotors can let them sit against the hubs slightly unevenly, or with some wiggle room, allowing them to vibrate as they turn. Another reason could be your brake pads shifting and allowing play in the contact between the rotor and caliper, allowing the vibration. This can be solved using brake pad shims or some of that brake pad lube they always try to sell you at your local auto parts store (though anti-seize works just as well).

What to look for when shopping brakes:

So let’s get into what you need to know in order to see past those flashing neon “BUY ME NOW” signs and actually find what works best for your specific needs. Hint: it’s probably not the most expensive thing on the market. A takeaway theme here will be to not spend more than you actually need, as those high-end, fancy race brakes are can actually be a real headache for normal street driving.

Narrow down brake pads by how you drive, not by price.

Brake pad choice is similar to choosing a tire. There’s no glory in getting something outside of your driving style. All you end up with is an expensive compromise.

This works both ways, too. You might think you’ll be doing yourself a favor and be safer buying expensive heavy-duty pads for daily driving, but what you could end up with is loud, annoying pads that dust like crazy and have worse cold bite than your stock pads. By the same token, if you’re doing a lot of towing or track days/autocross, you’ll be let down by a light-duty pad that will fade after the first round of hard braking — to the point of being dangerous.

Let’s break this down by use case:

Daily driver:

OEM replacement level is generally all you’ll really need. If brake dust and noise are pet peeves of yours, look into some ceramic pads, as they tend to have better street manners as far as that’s concerned.

Staff picks:

Posi Quiet Ceramic Brake Pads – Hard to beat for a basic OEM replacement pad. These are quiet, last a while, and are all around a safe bet for a commuter.

EBC Green Stuff – If you’ve got a daily driver that’s a little more sporty, or that you might load up and haul things with on the weekend, this is a great pad for someone who works their vehicles a little harder than the average Joe but are still mostly relegated to daily driving duty.

Spirited street/track use or towing:

Here’s where heat resistance starts to become a priority over street manners. Still, with the recommended picks below, you’ll be fine with day to day, but just know everything is a trade-off. Brake pad requirements tend to be pretty similar between towing and track driving. Both need to stand up to high heat over repeated cycles without fading.

EBC Yellow Stuff – This pad is an easy recommendation for anyone looking to take their car to a track day, autocross, or who tows heavy loads in mountainous areas. You don’t want to have to find out the hard way why they line the walls of the track with tires or how effective those gravel run-away-truck ramps are.

Hawk HPS – Generally a little more expensive, but feature Hawk’s own ferro-carbon composite pad material that offers a higher coefficient of friction, fights brake fade, and can be relied on to maintain grip and pedal feel lap after lap.

Let’s Talk Brake Rotors:

Next to calipers, rotors get all the glory. What shows people your car is serious better than some massive brake rotors that are the size of most people’s entire wheels. That look brings us to the elephant in the room, though. Those big brake rotors you’re picturing are drilled and mean looking aren’t they? Well, unfortunately that’s not exactly ideal if you’re looking to get the most out of your car. Let’s get into why:

Drilled and slotted rotors look awesome. They just do.

They look like the Jason Statham of brake rotors, for serious drivers who want to do serious things with their cars. The difference is J. Statham doesn’t crack under pressure, but drilled rotors do. Want an easy way to prove they’re more for looks than actual performance? Google around and look at any real race car’s brakes. IMSA, NASCAR, F1, WRC, you name it. You’ll see slotted rotors sometimes (especially in rally), but never drilled in anything that is competing at a high level.

So why do these serious performance cars like the Mustang GT350R, Porsches, or Ferraris have drilled rotors? The simple answer is that they’re for looks, and that they’re still strong enough that they won’t be a big problem for most drivers on the street. However, if you really push them to their limits, they will crack long before straight rotors will. If they are pushed hard, but not to the extreme, you get some pretty interesting wear patterns as well (more on that below).

So where did drilled rotors come from then?

They actually did come from legitimate racing needs, in fact. Way back in the day of asbestos brake pads (ignorance isn’t always bliss), there was an issue of outgassing with the pads under high heat. The issue is that the bonding agents in the pad would evaporate and create a layer of gas that prevented good contact between the pad and the rotor. The rather rudimentary solution at the time was to just drill a bunch of holes in those suckers and go racing — and that worked pretty well for the time.

The issue is that these days, we no longer use asbestos in our brake pads (no, not even Raybestos pads, despite the name), and with how far material science has advanced in this industry, outgassing is no longer as big of an issue as it once was. Also, pad manufacturers began putting slots down the center of their pads, reducing the need for those holes anyway.

But drilled rotors cool run cooler too, right?

Yes, drilled rotors do indeed tend to run a little cooler than straight-faced rotors, but here are two caveats to that fact:

1. The face of drilled rotor might have a reduced surface area of up to 10%-12%, which means there is overall less surface area for the pad to grip onto, meaning less friction applied in total, and not as much heat generated as a result. The cooling provided by those holes being there does make a slight difference, however, but that can be a bit of an issue in itself.

2. Due to those drilled holes catching air, the surface in those areas cool more than others, leading to cracks. Cast iron rotors expand and contract with heat, and the metal around those holes cools faster than the solid surfaces around them. This means that as the rotors cool, they are contracting at different rates around the surface of the rotor. What’s even worse is that the areas of the rotor that experience the biggest heat differentials are the narrow spaces between the holes of the rotor, where there is less material to spread the stress out across by their very design. It’s a vicious cycle.

That’s how you get cracked rotors as seen above. That cooling is a double-edged sword that, unfortunately, is sharper on the side facing you in the case of drilled rotors. Oh, and that uneven wear pattern I mentioned earlier, check out the rotors on this Porsche I saw at a stoplight just the other day:

So what about slotted rotors then?

Like I mentioned, slotted rotors are in fact found quite often in motorsports, even among serious race teams. There are a few reasons for that, namely the ability to provide runout for water, dust, and other debris (hence their popularity in rally).

Slotted Rotors:

Like I mentioned, slotted rotors are in fact found quite often in motorsports, even among serious race teams. There are a few reasons for that, namely the ability to provide runout for water, dust, and other debris (hence their popularity in rally).

However, slotted rotors are not without their own set of downsides. One issue is that the slots tend to accelerate pad wear, as they cut into the pad material over time. This means that your pads will need to be replaced more frequently compared to using smooth rotors.

Additionally, slotted rotors can be noisier than their smooth counterparts. The slots can create a humming or whining noise, especially during light braking. While this noise might not be a concern on the race track, it can be annoying during everyday street driving.

Smooth Rotors:

Smooth or blank rotors are the most common type of rotors found on vehicles, especially on daily drivers. They offer a few advantages that make them suitable for everyday use.

Firstly, smooth rotors provide consistent and even contact with the brake pads. This results in predictable braking performance and a smooth pedal feel. There are no slots or holes to disrupt the contact between the pad and rotor.

Secondly, smooth rotors tend to be quieter than slotted or drilled rotors. They produce less noise and vibration during braking, making for a quieter and more comfortable driving experience.

Finally, smooth rotors are less prone to cracking compared to drilled rotors. The absence of holes means there are no weak points where cracks can initiate. This makes smooth rotors a durable choice for everyday driving.

Conclusion:

When it comes to choosing brake rotors, it's essential to consider your driving style and needs. While drilled and slotted rotors may offer a sporty appearance and some performance benefits, they come with trade-offs such as increased noise and the risk of cracking. Smooth rotors, on the other hand, provide consistent performance, quiet operation, and durability, making them well-suited for daily driving.

Ultimately, the best choice of brake rotors depends on your preferences and priorities. Whether you prioritize aesthetics, performance, or a balance of both, there are rotor options available to meet your specific requirements. Remember to pair your chosen rotors with compatible brake pads for optimal braking performance.

About the Author:

This article was written by Garrett Davis, a contributing writer for AutoCraze. Garrett is passionate about automobiles and has a deep understanding of automotive technology. He enjoys sharing his knowledge and insights on various automotive topics to help car enthusiasts make informed decisions.

If you found this article informative and want to read more from Garrett, be sure to check out AutoCraze's blog for a wide range of automotive articles and guides.