Give Me A Brake - Brakes and Your Jeep
Give Me A Brake – Brakes and Your Jeep
By Justin Banner
You might not give it much thought and take it a bit for granted, but your Jeeps brakes are critical to its safety and performance both on and off-road.
Cars, trucks, and Jeeps all use brakes. It’s how we come to a stop, slow down, and keep the vehicle from rolling when we don’t want it to. They all work basically the same way: turning kinetic energy into heat energy by using the coefficient of friction between the pad or shoe material and the drum/disc surface to change it.
Are On-Road Brakes Different?
No, not really. The goals are the same even if the surfaces aren’t. However, there are additional goals to achieve by racing cars that most road cars and Jeeps won’t have to bother with. Though, it’s something to consider, too. Reducing the energy required to rotate a wheel and tire.
If you’re familiar with the on-road world, you probably are aware of the term rotational inertia. You’ll hear it a lot from the open wheel, sports car and autocross worlds more than you’ll hear anywhere else. Decreasing the rotational inertia could help with reducing stopping distance by reducing brake fade. It does this due to reducing heat by reducing the brake load and reducing the maximum traction required from the tires during a stop. Why does that happen, though?
The theory is that when you change your wheels and tires to something larger and heavier, you increase the stress you’ve added to your brakes. When you increase the tire diameter, you increase the rotational inertia of the tire by both adding weight and increasing the overall circumference of the tire. So, while you gain height you also add more to stop rotating.
How much does reducing weight at the wheels help? When it comes to braking performance, it’s nowhere near as much of a benefit when compared to acceleration and power production at the wheels. Since you’re trying to take away inertia, slowing the wheel down doesn’t require any power. It just requires an exchange of kinetic energy for heat energy, which is why your brakes work at all. However, it should be mentioned that the less weight your brakes have to slow down, the better your brakes can work and increase their useful lifetime, even if it’s marginally better.
Changing Friction Compounds
If reducing the weight of the wheel and tire combo isn’t going to do much, then what is the next best option to improve your Jeep’s braking? You start with changing the original pads. The Jeep JK’s front pads are a ceramic compound while the rear set are semi-metallic. So, what does that actually mean and how do they compare?
What is this Stuff?
Your pads are made of two parts: the metal backing plate and the friction material – often referred to as the “compound.” The friction material of the pads and shoes are mixed with their adhesive prior to being flowed into a mold with the backing plates made of steel. They are then pressed to their shaped molds before getting sent to an oven.
They are then baked to very high temperatures with their compound and adhesive with the addition of a rough surface on the backing plate to promote adhesion and mechanical bonding. This bonds the backing plate and friction material together in the modern brake pad and shoe. Prior to this method, and in a few extreme cases today, the friction material is pressed into a mold with openings for rivets, which fastened them to their backing plates instead of using adhesive.
Friction material can also be molded into the backing plate itself and use little to no adhesive in what is known as “Positive Mold” technology. This allows pads to have a more consistent density of friction material over the life of the pad as well has use higher pressures to attach the friction material to the backing plate. This also reduces the issue of adhesive gassing, which we’ll discuss later in this article. You’ll notice this type of pad by seeing some of the friction material in holes through the backing plate.
Now, what are each of the common types of compounds?
Semi-Metallic, often mistakenly called or referred to as “metallic,” brake pads are about 30- to 60-percent metal with other synthetic compound mixtures within the friction material. It is a very good material to look for if you do a lot of braking or do very heavy braking. Something like stop-and-go traffic or heavy towing.
This comes at a cost, though. Because of the amount of metal in the friction material it can be harsh on your rotors. These also may not perform as well in very cold temperatures as they won’t generate enough heat to cause friction and won’t bite. At least initially; once you use the brakes several times, they will begin to generate heat and work as they were intended.
This type of compound is used on the rear of your factory Jeep Wrangler. Since the rear doesn’t get used at the same pressure as the fronts, the wear and harshness aren’t as bad as it would be for a front brake pad. The lack of initial bite is also not an issue for the rear as the package is designed for temperatures seen for rear brake use.
Organic Brake Compound
“Organic” pads are made of materials such as fiber, chopped glass, mineral fibers, and even Kevlar mixtures and, thus, the “organic” naming. So, no, they aren’t free range, GMO-free, vegan pads as we’re sure you want to make a dad joke out of.
These pads are usually low-dust, low-noise, and are generally better on the rotors, but they do tend to wear out fast. They are also not good for brake environments that see a lot of heat because of their high-content of non-metallic materials.
Those materials ablate away as you increase the heat and use the brakes more and more. You’ll usually see these advertised as a “low-cost” or “economy option” brake pad as they are inexpensive to produce over semi-metallic, low-metallic, and ceramic pads. Because of their compound, they are good in low brake temperature environments where the brakes aren’t used that often.
Low-Metallic Brake Compound
The low-metallic pads you see on the market are called so because they don’t contain as much steel as Semi-Metallic Pads. Sometimes they contain no steel at all and those contain a lot of the same mixtures as organic pads. However, they perform better because they are mixed with more copper or other types of softer metals. So, these pads will be a little noisier compared to organic but not as much as semi-metallic pads.
They are also not as harsh on rotors as semi-metallic pads are, but again will wear the rotors faster than organic pads. These are, as you can probably guess, in between when it comes to brake temperature environments. They work far better at low brake temperatures than semi-metallic and can stand higher temperatures than organic pads, but that does depend on the material mixture.
Ceramic Brake Compound
The ceramic brake pad is one that uses ceramic compounds along with some other metals like copper in its mixture. These are the stock front brake pads on your Jeep Wrangler. They provide the lowest dust and noise and have the lowest wear on the brake rotors. While they can take higher temperatures, they are not a desirable choice for a high-performance option. Reason being is that they don’t get rid of heat as well as metallic-based friction materials.
These are the best choice for the show Jeep that sees street duty and wants decent braking performance. However, there are also new ceramic compounds coming out of Europe that do feature more metal in their mixtures. This means that show and performance drivers can start having their cake and eat it, too. This idea of a true high-performance ceramic brake pad is coming down the line in non-OE applications.
Full Metallic and Exotic Brake Compounds
Finally, there is the true metallic brake pad compound, usually found in racing brakes. They are made of sintered metals with little to a non-zero amount of synthetic materials in the friction lining. They have a very high fade resistance and very high-temperature tolerances.
This also means they are noisy and are very harsh on rotors as well as require a higher temperature to begin to operate properly. There are also exotic material brakes made from carbon fiber, however these types of pads and rotors need to generate high-temperatures to operate and are best suited for harsh race track environments. Carbon fiber pads also can’t be used unless it’s with a carbon fiber rotor.
There is the Carbon Ceramic brake pad, but it’s not as complicated or exotic as it sounds. It’s essentially a ceramic compound with some carbon fiber mixed into the compound. It’s there to reinforce the compound and not increase brake temperatures by any significant margin over ceramic compound pads.
Shapes and Design Features of the Friction
Brake pads come in many shapes for many reasons. While caliper and packaging design plays a significant role, it’s not the only reason.
A common design among street brake pads is the chamfer, an angled cut seen at the ends of the brake pad friction material. There are several ways a chamfer is done and is designed to prevent high-vibration areas around the edges of the brake pads when they contact the rotor. This reduces the noise and vibrations you can feel while stopping when compared to a brake pad without the chamfer. A pad with a straight edge design on the braking area usually causes a high pitch squeal from a phenomenon called “tip drag.”
As the piston of your caliper begin to push the brake pads into the rotor, the pads begin to bend and fluctuate. This happens in microns of an inch but can create the high frequency squeal as the pad tips bounce against the rotor. This bouncing can create glazing on the rotors and even increase rotor wear. A straighter edge has the tendency to bounce and grab more than chamfered edges which can lead to noise and can cause pad lift. Pad lift is where the friction material lifts off the backing plate and this can cause moisture to build up, leading to de-bonding from corrosion, corrosion of the backing plate, and brake pad failure.
Cuts in the Friction Material
The center cut on the brake pad friction that you see in this picture is designed for three reasons: flexibility, cooling, and venting. Even with the chamfer, the pads will still move and bend on their backing plates. If a solid piece of friction material is used on a pad that moves quite a bit, it can lead to chunking of the friction and even full pad failure. The slot also helps the hot gasses that build up to vent out and help prevent the pads from overheating in hard-use cases.
This same venting will allow the incandescent material – the unburnable debris from pad wear and road pickup – to vent out and away from the rotor and pad for optimal braking performance. In some cases, pads can have more than one cut for the same reasons. It all depends on the design requirements of the caliper and backing plate interaction as well as venting requirements.
Rotor faces come in four distinct types: solid, slotted, cross drilled, or slotted and drilled. How do each of those work and what are the advantages of them?
Solid Face Rotors
A solid face rotor will be the most rigid and can dissipate heat very well. It can take a little more abuse and can also be resurfaced easily from “warping.” It’s the simplest design that all OEs take advantage of because it doesn’t require extra machining or complex work to build or mold it. While it’s simple, it’s still very effective in most high-performance brake systems where debris clearing isn’t an issue and you need to remove heat from the brakes quickly.
Slotted Face Rotors
A slotted faced rotor is designed to keep some of the rigidity and heat dissipation of the solid rotor but create a space for incandescent materials to be wiped away from the friction lining. It can help with some degassing. Those gasses come from the natural breakdown of the adhesive that holds the brake friction to the brake pad as it heats up from use.
This gassing essentially creates a bearing surface between the pad and rotor, like how an air hockey puck works, and creates a form of brake fade because the gasses can’t be compressed. The theory is that the slots transfer those gasses away from the friction and rotor surface along with the incandescent materials to improve braking performance in high-performance applications.
A street Wrangler normally won’t see this and you’ll only worry with this in your Jeep if you happen to race it. However, even in a racing situation, a solid rotor would be the better choice because it will offer the best heat dissipation and strength.
Cross Drilled Rotors
A cross drilled rotor has holes drilled straight across each rotor face that also feature chamfered edges to reduce hot spots at those drill points. The theory of this design is maximum degassing as the venting of the rotor helps pull those gasses away from the rotor surface. The problem you start to encounter with a cross drilled rotor is the reduction of surface area for cooling. This can cause heat stress cracks at the drill points and a loss of rigidity overall for the rotor.
With modern adhesives and pad construction, the requirement of a cross drilled rotor has been reduced to the point that they aren’t used that often in professional motorsports. The exception is environments where having high rotor surface temperatures are needed for brake pad friction effectiveness.
In other words, you don’t need a cross drilled rotor on your daily driver. The brake temperatures won’t be high enough for pad degassing and the pads you are using don’t need that much temperature to operate. If you’re using a full metallic compound on your street car, you’re not doing yourself a favor unless you’re heading for a track.
Slotted and Drilled Rotors
The combination of slotted and drilled seeks to gain the advantages of both: the maximum degassing of a cross drilled rotor and the wiping of the friction surface of the slotted rotor while also retaining some of the rigidity from the slotted rotor design. However, if you’re not experiencing any degassing issues with solid rotors, you’re not gaining much in terms of performance from switching to either version. You’ll also lose surface area that helps with cooling your brake rotors.
Both a slotted and cross drilled rotor will be slightly lighter, but only by a few grams at best. Unless you’re in a Formula Car or have maximized the reduction of the weight of your tires and wheels, losing weight at the rotor isn’t going to be of much use to you and can be detrimental if you don’t buy a high-quality slotted or drilled rotor.
Why Do We Offer Them, Then?
Structurally speaking, there is nothing wrong with using drilled, slotted, or drilled and slotted rotors. A street driven Jeep shouldn’t heat up the brakes to the point that the structural weaknesses become present and cause failure. If you want those rotors because the look cool, that’s fine. If you’re getting them because you want all out performance, you’re better served in other ways.
Losing Weight with a Two-Piece Rotor
If you want maximum rigidity but want to reduce weight, you should consider a two-piece rotor with an aluminum hat. The aluminum hat reduces the weight of the rotor significantly since that large mass of metal is of a lighter material.
You also gain the ability to change rotor faces and material without changing the rotor hats. This type of hat can allow you to work with a custom design by just changing the hat instead of the whole rotor. This does come at a price increase over a single-piece hat and rotor but if you’re going for maximum lightness, price usually isn’t a concern at that point. Again, it’s overkill for the typical street Jeep.
So, how do rotors “warp?” Well, they don’t warp like a wet piece of board does. What’s happening is that the pads are leaving some of their friction material on the rotor surface under harsh braking. Why does this happen?
Notice that “warping” is in quotation marks here. Your rotors do not warp in the sense that wood warps when it gets wet. Instead, what’s happening is that the brake friction material is transferring unequally to the rotor face. This can happen because of unequal temperatures on the surface of the rotor, a hotter spot on the rotor will transfer more friction material onto the rotor surface than the colder spot.
How a Rotor Cools
Rotors come in solid disc or vented disc, with most front rotors being vented. The venting design is a centrifugal (radial) fan type, where – in the simplest terms – the blades create a low-pressure area on the outside of the rotor as it rotates. The high-pressure area between the blades flows in to fill in that low pressure area, which then creates a low-pressure area behind that to pull in more air. Again, that’s over simplifying it. Changing the angle of the blades can increase efficacy but will make the rotors directional. There are also multi-blade designs that direct airflow for better hot spot cooling.
Those hot spots create those uneven surface temperatures that causes friction material to transfer onto the rotor surfaces. This then causes the judder and vibrations associated with “brake warping.” When a technician resurfaces the rotor, they are removing that access material along with the rotor surface to create an even face again. That’s not to say a brake rotor can’t warp, but if it does there’s a whole host of other problems going on and usually the rotor will crack and break before that warping happens.
So, What About My Jeep?
It’s mostly situational when it comes to improving braking performance of your Jeep. If you’re running a street Jeep, staying with the stock setup of a ceramic front pad with a semi-metallic rear and solid faced rotors is your best bet. A lighter tire or wheel and tire package could help, but it will be marginable at best.
If you’re looking to crawl with it, swapping up to a semi-metallic front pad would be better as you’ll be able to use it at a lower temperature than a ceramic with better performance. However, you’ll want to stay with a solid face rotor, even an OEM Jeep one. Weight usually isn’t an issue, but if you want to reduce it, look into the wheel and tires then go to a two-piece rotor.
If you’re in Jeepspeed or anything that gets you up to speeds over 80-MPH in the dirt, you’ll want to switch to a proper racing pad. This means something with a large amount of metallic compounds in the friction material. If you’re struggling with creating heat in this environment with that metallic pad but need the bite this compound gives you, a slotted rotor would be your first step before going to a cross-drilled one. If you want to reduce the weight, consider a two-piece rotor with an aluminum hat.
However, no matter where you go, you can get some of the best brake products from us here at Vicious Off-Road. Rugged Ridge, Alloy USA, Currie, and more continue to be added as we expand our resources to provide you with the best parts in the business for your Jeep!