Brake System Design and Optimization: Upgrading Calipers
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Upgrading Calipers
10.07
| 00:00 | - Besides a big set of motorsport style callipers looking impressive behind the spokes of our wheels, there's a range of performance related reasons why we might want to upgrade our brake callipers. |
| 00:11 | Callipers are responsible for converting the hydraulic pressure from the brake lines back into the mechanical force to clamp the pads against the disc, essentially providing the normal force for the friction. |
| 00:24 | While this function is relatively simple, the callipers' architecture and features have a big impact on the resulting performance, serviceability and reliability. |
| 00:35 | We discuss some fundamental knowledge on callipers in the components section of this course so if you need a refresher I'd recommend revisiting before getting any further into this module. |
| 00:46 | The most common reason people want to upgrade their callipers is to improve braking power. |
| 00:51 | As we know from our discussions on friction and brake bias, this can be achieved in multiple ways. |
| 00:57 | In relation to the calliper though, this is really a case of increasing the normal force between the pads and the disc which is a result of the clamping force from the callipers. |
| 01:07 | As we know, for a certain force applied to the brake pedal, the master cylinder converts this into a certain pressure in the brake lines. |
| 01:15 | Pressure equals force over area which can be rearranged to force equals pressure times area so we can see that an increase to the total calliper piston area on one side of the calliper results in a greater clamping force for the same pressure and therefore pedal effort. |
| 01:33 | Essentially we're giving the driver more leverage over the brakes. |
| 01:38 | The volume of fluid required to move the pistons a certain distance and engage the brakes also increases but we'll come back to this soon. |
| 01:46 | Alternatively, let's say the brake torque our current setup can generate is sufficient and we know this since we can lock all four wheels relatively easy. |
| 01:57 | Clearly we need more grip to increase the actual rate of deceleration but there are still other reasons we might want to upgrade our callipers such as reducing compliance, weight and uneven pad wear and increasing the thermal capacity and resistance. |
| 02:13 | There's a lot of callipers out there, both from the OEM and the aftermarket but how do we choose which callipers are suitable for our application? Let's start with the piston area as this is probably the main point we need to consider. |
| 02:27 | And it's not always a case of bigger is better, particularly when we're retaining the factory ABS system. |
| 02:33 | In this case, the total piston area on one side of the calliper and the ratio of this area between the front and the rear brakes needs to remain close to that of the factory spec as the ABS will generally be able to compensate for relatively small changes and still work effectively but major changes could spell trouble. |
| 02:55 | Without ABS, things are a bit more flexible but the same ideas still apply. |
| 03:01 | Assuming we aren't changing master cylinder sizes, if we increase the piston area, the system needs to displace more fluid volume to engage the brakes and therefore more pedal travel is required. |
| 03:15 | Too great of a change from the factory spec means we'll need to change our master cylinder size to compensate which is something we covered in the previous module. |
| 03:23 | As well as retaining the calliper piston to master cylinder area, front to rear to avoid changing the brake bias. |
| 03:31 | It's very common to upgrade the front callipers while retaining the factory rear setup. |
| 03:37 | Specifically in more front weight bias cars like front wheel drives where the front brakes are doing the majority of the work and the improvements result in bigger gains. |
| 03:47 | The question is, how do we retain the balance when doing this? In this case, the best way to ensure balanced braking performance is to maintain similar front to rear bias as the factory setup and this means avoiding an increase in the front brake torque. |
| 04:03 | For example, increasing the disc diameter while moving from a single piston sliding calliper to a four piston calliper that has two pistons per side with a reduced total piston area. |
| 04:17 | The brake torque could remain unchanged while increasing the stiffness, thermal capacity, performance pad availability and so on. |
| 04:26 | With all that said, we do need to consider that if the car has increased tyre grip, it may be able to pull higher G force on deceleration and therefore the load transfer would be greater and an increase in front bias might be desirable. |
| 04:42 | On the other hand, a lower centre of gravity or lighter vehicle weight when compared to the factory specifications could mean less load transfer so more rear bias would be desirable. |
| 04:54 | In either of these cases, we would upgrade the callipers with these changes in mind. |
| 04:59 | A key challenge to consider here when moving to bigger brake callipers or discs is making sure they fit under our wheels both radially and laterally. |
| 05:09 | By radially, we're talking about the brake package fitting inside the inner diameter of the wheels and the disc diameter has a big impact on this as well. |
| 05:18 | It's common for an upgrade in brake size to require a move upwards in rim diameter which can introduce its own set of complications. |
| 05:28 | By laterally, we're referring to the calliper fitting behind the spokes of the wheel. |
| 05:33 | Some vehicles are more susceptible to issues here, depending on how the brakes fit with the hubs. |
| 05:39 | It's common for the calliper to wheel clearance to get pretty tight here but I'd recommend aiming for at least a few millimetres of clearance to allow for some movement with components flexing and thermal expansion. |
| 05:51 | Alongside this, we also need to consider how the calliper mounts to the suspension as it's unlikely an alternative calliper will bolt up to the factory mounting point. |
| 06:03 | Depending on the application, sourcing a big brake kit could be a possibility and make the upgrade somewhat of a bolt on affair. |
| 06:11 | Alternatively, we'd need to design an adaptor bracket and there's a few things to consider if going down that route. |
| 06:18 | Firstly, will we be able to make this new calliper fit without introducing more compliance? We don't want to spend money on some nice stiff monoblock callipers just to attach them with a flimsy bracket that'll result in more compliance than the factory setup. |
| 06:33 | Motorsport callipers tend to have radial mount fixing where the mounting hardware is parallel to the disc as opposed to axial mount fixing which is where the hardware is parallel to the axle. |
| 06:45 | Either method can work fine, depending on your application, it's just important to know what you're buying. |
| 06:51 | In terms of calliper positioning, this mostly depends on the diameter of the brake disc, but its position and alignment to the disc are also important. |
| 07:00 | In the radial direction, to ensure the edges of the brake pad line up with the edges of the disc, we should avoid any more than half a mm of misalignment in either direction as this would cause sharp raised edges as the parts begin to wear. |
| 07:16 | The calliper needs to be positioned laterally to centre the calliper over the disc. |
| 07:21 | This means the pistons will move an equal amount when the brakes are applied which minimises the maximum distance the pistons will extend. |
| 07:30 | Likewise, the pistons also need to be square to the disc's surface. |
| 07:35 | Both of these prevent the pistons from misaligning with the calliper and damaging the pistons, callipers or seals and also helping to reduce compliance and poor pad wear. |
| 07:46 | Suppliers will specify a recommended disc diameter and thickness range that's suitable for their callipers and will ensure the best performance and reliability. |
| 07:57 | They'll also be able to provide a technical drawing with dimensions and sometimes even a template that will allow us to check the fitment with your suspension and wheels as well as helping you design mounting brackets. |
| 08:11 | Along with this information, suppliers should provide suitable pad shapes. |
| 08:15 | All of this is important to understand before committing to any purchase and then considered once the components are being fitted and set up on the vehicle. |
| 08:25 | Another point to quickly note here is that some callipers are directional, usually when they have staggered pistons as the smaller diameter pistons need to be at the leading edge of the brake pad. |
| 08:37 | Lastly the bleed nipples need to be at the highest point of the calliper to allow for effective bleeding of the brakes. |
| 08:43 | In a lot of aftermarket performance callipers, we'll see bleed nipples on both ends of the calliper which helps the manufacturer reduce costs associated with variation. |
| 08:54 | Or bleed nipples on one end and a bridge pipe across the other which can usually be swapped around if required. |
| 09:01 | We've covered a lot of information in relation to upgrading callipers in this module so let's recap the key points. |
| 09:09 | Pedal feel and brake bias must be considered when changing the callipers as changing the piston area at one end of the vehicle will require compensation at the other end. |
| 09:19 | Significant changes at either end could also require changes to the master cylinders. |
| 09:25 | Besides the hunt for more braking power, there are wide reasons why you might want to upgrade your brake callipers that will have a significant impact on the performance, reliability and serviceability. |
| 09:38 | The mounting method, be it axial or radial, and how the calliper is positioned relative to the disc also needs to be considered all while making sure they fit behind the wheels. |
| 09:49 | With al these points we've covered in mind, you can start to spec appropriate piston sizes and determine what features you actually need and how this will suit your budget, while also considering the costs of operation in terms of brake pads and servicing. |
