Everyone is probably familiar with the popular phrase that says: “cropping leads to loosing. In literary Russian it means that an attempt to save money may result in such losses, which many times exceed the inappropriate savings. In cars, one of the clear illustrations of such “croilow” is the economy on brakes, and especially on brake pads. Experienced drivers, however, do not do so and remind that the cheapest pads last less. And the very experienced also say that such economy sometimes ends with braking into a pole or the rear beam of a truck. Maybe they’re being dramatic. Let’s unravel the intrigue and see what the catch might be.
It’s not that simple.
To understand that even something as trivial as brake pads isn’t really that simple, just remember what pads do and under what conditions they work. At a basic level, everyone remembers that the pads press against the brake disc and thus slow it down. But we need to dig a little deeper. Firstly, the pads work at extremely high temperatures: the brakes heat up to several hundred degrees during intensive work. At the same time the pads have to maintain a stable coefficient of friction with the disc over a wide temperature range, not to crack, not to burn, not to crumble, and, you see, not to squeak. The coefficient of friction is a dimensionless value that characterizes the effectiveness of braking. The higher it is, the shorter the braking distance of the car. However, as the temperature increases, as a rule, the coefficient of friction decreases. At the same time the braking efficiency decreases. Brake pads not only have to deal with water and dirt, but also road chemicals. In addition they need to isolate the brake mechanism from heating from the disks: the brake fluid is of course designed not to boil at temperatures up to 230-250 degrees, but the wheels may be heated to higher marks. At the same time the pads should provide an optimal friction coefficient, but at the same time not be too abrasive, so as not to wear out the brake disk excessively. In general, the working conditions are nightmarish, to the point of being mutually exclusive. However, many pads cope with them. How do they do it?
First of all, it’s a design developed over the years. Again, let’s start at a basic level: everyone remembers that a pad is an overlay of abrasion material on a metal plate. The pad is officially called the friction layer – it’s the one that has to do most of the work we listed above. The metal plate is self-explanatory: it’s a steel base that’s attached to the brake mechanism. Between the base and the friction layer is another important element: the adhesive layer that holds them together. This ends the structure of the pad for many people – but what else can be added here? In fact, there is a lot more. The next important layer is the thermal insulation: it is applied to the steel base and is designed to further isolate the brake mechanism and fluid from the heat, in addition to performing a damping role, reducing the level of vibration and, consequently, the risk of squeaking when braking. Another – noise-insulating: it is either a pad or a special high-temperature mastic on the back of the pad. Well, and the finishing layers – anti-corrosive and lapping: the first covers the entire pad, except the working surface, and the second, by contrast, is part of the surface structure of the working surface of the friction material. However, if the thermal insulating layer – a must for large manufacturers of quality pads, the rest – already “optional”: their presence may depend on the technological level of the manufacturer or the price category of pads.
So, we found out that the friction layer has the biggest and the most complicated set of tasks. What does it consist of? There is no single and exhaustive answer to this question. Firstly, because its composition varies from manufacturer to manufacturer. And secondly, even one manufacturer has a great many variations of friction material composition for different tasks, product lines and end users. Nevertheless, it is possible to identify the main substances that allow the friction layer to perform its tasks. These are the bonding fibers that provide strength; elastomers that reduce brittleness; abrasives that increase friction coefficient; lubricants that allow the pad to slide on the disc and reduce unwanted vibrations; and fillers and bonding adhesives that provide a homogeneous structure and a strong bond between the components. If we talk about the composition from a factual point of view, we can mention components such as graphite, steel wool, aluminum oxide, Kevlar chips, nitrile rubber and so on.
In addition to the features of the composition, the friction layer can benefit from design features. The simplest option is a groove on the working surface of the friction material. This groove mainly serves to reduce the internal stress of the material when heated, allows the removal of wear products from the working area and can also be used in the pad design to reduce the likelihood of squeaking when braking. The second design feature of some pads is the removal of a chamfer on one or both sides of the friction liner. This technique allows you to facilitate the running-in of the disc and pad, and to reduce the vibration background, which provokes noise and squeaking when braking.
Does all of the above help the pads do their job absolutely perfectly? Under ideal conditions, yes: if the pad is made according to all the rules, and the operating conditions remain within design limits. In real life, however, things don’t always go as planned and the pads have to go even tighter. For example, a long descent down a mountain serpentine in a hot summer day is a pleasant emotion for the driver and a personal hell for the brakes. Slushy winter, when a mixture of water, dirt, reagents, combustive-lubricating materials and other stuff is accumulated on roads day after day – it is hard time not only for the body, but also for brakes. Well, and trivial wear and tear can not be written off too: even if not to speak about conditions, when a careless rider rolls out the pad to the metal, excessively worn out pad works less effectively. Let’s talk more about why pad quality comes to the fore in tough conditions.
What’s wrong with cheap pads?
In general, the answer to the question “what’s wrong with cheap substandard pads” is simple: literally everything. You can take the list of challenges and problems above and add a minus to each of them. In fact, that’s what we’re going to do now.
First of all, cheap pads are an ineffective composition of the friction layer mixture. In this case we can not even talk about ecology: economy and ecology are almost always mutually exclusive paragraphs. In fact, up to a certain time nobody thought about ecology: at the dawn of their development, in the early 20th century, pads were made of asbestos fibers and phenol-formaldehyde resin. By the end of the last century, however, the carcinogenicity of asbestos had become a well-known problem, so its impending ban became clear to all. Leaders of the industry began to develop alternative compositions: so, Ferodo already in the beginning of 80-s has let out the first in Europe brake pads not containing asbestos. In this century the ban on its use was imposed by almost all major states, so that modern pads, if we do not take into account outright counterfeit, do not have it in their composition.
We have already talked about the composition of the friction material above, but we can add something else. In terms of composition, most modern friction pads can be roughly divided into low steel, semi-metallic and organic. In fact, the categories require a minimum of explanatory comment. In low steel pads, as the name suggests, the friction mixture contains a small amount of steel fibers, including corrosion inhibitors and abrasive materials. In semi-metallic pads, a significant portion of the friction composition is made up of metals – in particular, steel fibers (>50%) and graphite, without the use of special abrasive inclusions. Organic pads do not use steel fiber and the abrasive particles are present in a finely dispersed form. Following the toughening of environmental standards, modern friction materials are made with low or zero copper content. Just Ferodo specialists were among the first to develop and implement the technology of friction materials production with such a high copper content, which was named ECO-FRICTION. All pads of Ferodo Premier series are produced with this innovative technology. There is another group of highly specialized friction materials designed for high-performance brake systems, designed to work under extreme conditions. These, among other things, use an increased content of ceramic inclusions. The threshold operating temperature in such brake systems can be around a thousand degrees, so pads made of such materials work already in combination with carbon-ceramic brake discs.
If we go back to the cheap pads, in terms of their performance, everything becomes clear. Weak grip of the friction layer with the brake disc is only the tip of the iceberg. First, it can also be heterogeneous depending on temperature – already low-performing pads can perform even worse when heated. When it gets very hot, the situation can be exacerbated by the “gas cushion” effect from the evaporating resins at high temperature – in which case the braking efficiency drops to almost zero.
Poor wear resistance is the next disadvantage of cheap pads. Modern car owners are spoiled to some extent, and they demand from pads not only quietness, but also cleanness of disks. If the pads get too dusty, they are scolded, because they are not easy to get to a car wash, and the black dust adheres to the wheel rims. Besides, the dust from pads is not only an aesthetic problem, but also contaminates the brake mechanisms. Well, add to this the fact that “dusty” pads are, as a rule, rapidly wearing pads, and the picture of bad economy takes shape by itself.
In the context of pads losing efficiency while working, you can think of a phenomenon that is absolutely unacceptable for pads: their tendency to overheat. If cheap pads “burn”, all hell breaks loose: overheating means the destruction of the friction layer structure and the pad as a whole, and the loss of braking efficiency in times, and in addition the possible boiling of the brake fluid, especially if it has not been changed for a long time, and it contains a high moisture content.
The next illness of cheap pads is the increased aggressiveness to brake disks. Indeed, one of the ways to increase the friction coefficient of the pad without much cost is to trivialize the abrasive content. For the manufacturers of cheap pads it is not so important that the scale is shifted to the other side, and already the pads begin to actively wear the discs. Well and with active operation all this is fraught with overheating of discs and calipers, and the subsequent deformation of discs. The overheated discs cause brake beating, and the next step is their replacement or, to a lesser degree of probability, shimming. There is nothing to say about the fact that the pads of increased abrasiveness are also prone to noise during braking: against the general background it is just the trifles of life.
In general, we have not made today almost any amazing discoveries for anyone, but simply repeated the simple truths and backed them up with theory. Therefore, the conclusion from the above will be simple: in fact, a lot of savings on the cheap pads do not work. At best, the savings will result in a lower service life, and therefore in more frequent changes of pads, and that is already an additional expense. In a more unfortunate variant it is possible to kill disks and to face even more expensive service of brakes. Well and at the most negative scenario it is possible to kill not only something. In general, it is not necessary to save money on brakes – it is not worth it. And what is worth it, so it is to take time to choose high-quality pads – for example, from brand Ferodo. The manufacturer of this product for over a hundred years has accumulated tremendous experience in the creation and production of parts of the braking system.