Brake System Design and Optimization: Brake Bedding
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Brake Bedding
07.39
| 00:00 | - The term brake bedding refers to the process of preparing the brake pads and discs to work properly together. |
| 00:06 | This procedure is sometimes misunderstood, both in terms of the true purpose and the appropriate technique so in this module we'll be discussing the correct bedding process in order to clear things up. |
| 00:19 | Brake bedding is a process we can carry out on new brake pads and discs but it's primarily about properly preparing the disc for racing use. |
| 00:29 | For motorsport brakes, the bedding process is critical to get the required performance level and longevity out of the brakes. |
| 00:37 | The first thing to understand about bedding is that it's not so much about getting the pad and disc surfaces prepared to work together from a mechanical perspective, the important thing that's actually going on during the bedding process is a chemical reaction. |
| 00:52 | Before we discuss the process itself we need to understand a little more about the mechanisms that give us the frictional forces we want between the pad and the disc. |
| 01:03 | There are 2 at play here, molecular bonding and abrasion friction. |
| 01:08 | The abrasion mechanism is due to the structure of both the pads and the discs being torn apart at the interface between them when the pads are being squeezed against the discs. |
| 01:19 | It's the forces required to break the bonds between the particles that gives the abrasion mechanism its retardation force. |
| 01:28 | This is also the mechanism that makes the pads and the discs wear out as we use them. |
| 01:33 | The molecular bonding on the other hand is due to the molecular attraction between like molecules that occurs when they're brought very close together. |
| 01:42 | We already understand that for conventional iron discs, we have pads and discs that are made from highly dissimilar materials so if these materials are so different, how do we have like molecules bonding together? The answer lies in having an even layer of brake pad material being transferred from the brake pad to the disc. |
| 02:04 | When a very thin but consistent layer of pad material becomes embedded in the disc, this means we now have like materials in both components. |
| 02:14 | As the disc wipes over the surface of the pad with some pressure applied, these bonds are being made and broken continuously. |
| 02:22 | This is the source of molecular bonding friction forces. |
| 02:26 | Both of these mechanisms are at play during braking and it's the differences in the make up of the pad material that will determine how much of the brake friction force is made up by abrasion vs molecular bonding. |
| 02:40 | In motorsport brakes, we want to maximise the molecular bonding mechanism which is typically more stable at the higher temperatures we experience. |
| 02:49 | It's the process of brake bedding that's responsible for the even and consistent pad material transfer to the disc surface. |
| 02:57 | Without this layer, we can't take advantage of the molecular bonding. |
| 03:01 | It's important to understand that every brake manufacturer has a specific procedure documented to properly and completely bed in a new set of brakes that should be followed. |
| 03:12 | Obviously we're not going to go through each and every one so in order to keep things brief, let's look at some general best practices. |
| 03:21 | When new brakes are fitted and need to be bedded, the first step is to gradually bring them up to temperature. |
| 03:27 | We want to slowly warm the brakes to avoid any thermal shock or high temperature gradients. |
| 03:32 | If the pads are new as well, this helps to initially condition them wiht what's often referred to as burning off a new set of pads. |
| 03:41 | After the temperature is high enough and the components are sufficiently warm, the bedding process can begin. |
| 03:47 | This is made over a series of stops. |
| 03:50 | The first being moderate in both initial speed and pedal force. |
| 03:54 | These stops will then be gradually ramped up in both the initial vehicle speed and pedal force. |
| 04:00 | The bedding process is usually spread out over 10-15 stops. |
| 04:05 | This means you're usually spending around 2 laps on an average track to complete the bedding process after you've completed your warm up. |
| 04:14 | Once the bedding is complete, the brakes need to be cooled gently and evenly which is an extremely important step. |
| 04:22 | The cooling down should happen over 1-2 laps depending on the lap length with minimal braking energy being used. |
| 04:30 | It's critical the brakes are allowed to cool sufficiently before coming into the pit lane. |
| 04:35 | While that's a general overview of the procedure the manufacturer's recommended process for your particular brakes should always be followed, the procedure from the manufacturer will also often give you some reference images of what a successfully bedded disc should look like. |
| 04:52 | While brand new unused discs will usually have a silver, bare metal colour, a properly bedded disc will tend to have a grey or dark tinge to it. |
| 05:02 | This colouring should be even and consistent across the whole swept face of the disc. |
| 05:08 | This indicates that we've achieved an even transfer of pad material to the disc face. |
| 05:14 | A number of problems can be caused by not correctly and completely bedding a new disc. |
| 05:19 | Including vibration and poor friction characteristics. |
| 05:22 | We'll cover some of these in more detail in later modules. |
| 05:26 | Some brake manufacturers will also offer their discs in a pre bedded state. |
| 05:31 | This is where the discs are bedded with a pad of identical material to what will be used on the car. |
| 05:37 | This is carried out on a machine that's able to replicate the bedding process without needing to be fitted to the car. |
| 05:44 | This process varies by brake manufacturer and the reality is that even when a new set of brakes is pre bed, we often still need to carry out a bedding process of our own on the car to get the most out of them. |
| 05:57 | It's also possible to bed in a new set of discs with a used set of pads. |
| 06:03 | Again, the important thing here is that the material of the pad we used for the bedding process must be identical to that which you plan to race with, otherwise the bedding process will not be successful. |
| 06:15 | As the majority of braking energy will almost always be absorbed by the front brakes, bedding them isn't usually problematic. |
| 06:23 | However, in some cases it can be difficult to build sufficient temperature in the rear brakes to fully carry out the bedding process in one go. |
| 06:32 | This is particularly true of cars with a significantly forward weight bias. |
| 06:36 | During heavy stops, there just simply isn't sufficient energy being absorbed by the rear brakes to reach the temperatures required. |
| 06:44 | To some extent this can be helped with a specific driving technique, reducing rear brake cooling in an artificially rearward bias but it can remain challenging in some situations. |
| 06:56 | In summary, bedding the brakes is essential in order to achieve the optimal friction forces and therefore braking performance between new pads and discs. |
| 07:06 | The general process involves gradually bringing the pads and discs up to temperature and then completing 10 to 15 stops initially from a moderate speed which is gradually increased with successive stops. |
| 07:20 | It's then important to gradually cool the brakes before parking the vehicle again. |
| 07:24 | As a result, a thin layer of pad material is embedded in the surface of the disc which allows for molecular adhesion between the pads and the disc and therefore increases the friction forces. |
