Next in line on the papers for this thread....
Bedding your brakes
First off, I am sorry if my papers come across as simplistic. If you've been into cars for a long while then I'm probably just saying things you already know, but if you're new to cars then hopefully this information will help. Instead of hammering everyone with a bunch of numbers that are difficult to understand I like to keep things simple so everyone can follow along. In this I ask folks to be patient and remember all of us were new to this at one point in time. -Clint
They slow down the car. This can be kind of important, and we have to discuss a bit how they do it.
Ask anyone who drives a car, and they'll answer (I would hope) that the brake pads or shoes clamp down on the rotor or drum (that round thingie), and it makes the car stop.
So, what's really happening here? Well, in a nut shell we are converting energy. We're taking kinetic forward (or backward) energy of the car moving down the road, and we're slowing it down by using friction to generate heat.
So, we're making things hot. Sometimes really hot. That heat then dissipates into the surrounding air.
That friction is created by putting a clamping force between two materials, and it's how those materials interact that I'm going to discuss at this time.
We'll stick with pads and rotors for this one as that's going to be easiest to follow since you can go out to your car and look at them pretty easily.
You have a pad. It consists of a backing plate (the metal part on the back), and some kind of ablatable material. That material is made to wear away over time, and depending upon the compound of that material you can get different friction properties.
Some of those properties to consider are:
- Heat range
- Initial bite
I'll be going more into pad compounds in a later paper so we'll keep this one generic in regards to types of pads and compounds. For now just follow along that there's a material on the pad that rubs against the rotor.
This material wears away over time. This is on purpose. When you have two things rubbing on each other something has to give, and in this case this is the give.
So, we have a pad with backing plate, and some kind of friction compound.
Next is the rotors, and these are fairly simple in explanation as well (although not so much in engineering as demonstrated by the thousands of makers out there). In simple terms these are a metal disk that is attached to the tires though some kind of mechanical path.
Let me clarify that Ė the tires are whatís on the ground. They are what determine grip in terms of stop, go, and side to side. They are a vastly important component of any kind of handling characteristics of the car and will be the topic of a rather extensive paper in the future.
In order to stop the car the brakes have to interact with the tires somehow. In our case the rotors spin with the tires, and the pads are in a fixed location relative to the rotor. Also in our case the rotor in housed under the wheel, and is attached to the hub via the wheel studs so the rotor is clamped between the wheel and the hub.
As an aside there are other configurations out there, and historically many have been tried. Some examples are:
- Inboard brakes with the rotors on the axles.
- Brakes on the driveshaft
- Friction compound the spinning bit, and the metal surface clamping down on it.
So, anyway, rotors and what they are. As I said in very simple terms they are metal disks that the friction surface of the pads rubs on. Rotors can come in a few different configurations. Common are solid and vented. Solid is as the word implies in that itís a disk thatís completely solid. Vented is a little bit different. Think of two disks separated by some pillars to allow an air gap. The vanes for venting can be any number of configurations, and many are specific to who makes the rotors and their intended purpose.
As for materials on rotors thereís a few different ones out there. Cast Grey Iron (CGI), Stainless steel, carbon ceramic, cobalt steel (not really used much, and personally Iíd like to play with it someday), silica carbide doped steel.
In our case, and for a majority of folks out there, weíll be dealing with CGI. If you start digging into brakes and CGI youíll find that for the cost of the material, and how long itís been around itís actually pretty darned impressive. Perhaps thatís why itís been around for so long.
Further on rotors is the surface type. Thereí s a boggling array of surface types out there, but they all boil down to a few basic types and variations of them. Those are:
- Plain faces
- Cross drilled
- ďWaveĒ style
Iíll be doing a paper on these later on, but for now weíll just call a rotor a rotor.
So, here we have a rotor, and itís function in brakes is to do two things. First, hold heat and second, dissipate that heat into the surrounding air.
When I talk about holding heat thatís exactly what I mean. Everything has what is called a heat capacity which is basically how hot you can make it before it starts to fail. Failure in this case being defined as its ability to retain its shape and continue to operate as intended. In the case of rotors that heat capacity is made up on two things Ė material and weight.