Suspension Tuning & Optimization: Purpose and Role of Suspension
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Purpose and Role of Suspension
06.51
| 00:00 | - Suspension is a deep and sometimes complicated topic to fully understand. |
| 00:04 | But its purpose is very simple, keep the tyres in contact with the road and isolate the chassis as the car traverses terrain. |
| 00:12 | What's important to understand is that while the broad purpose of the suspension of a road car versus a race car are similar, we place very different priorities on each. |
| 00:21 | In road cars, design is to prioritise passenger comfort, lower cost, ease of manufacture, stability, durability and even cabin space. |
| 00:31 | Of course, some effort is put into performance depending on the model but this still tends to be heavily compromised in favour of everything else that goes into a good road car suspension. |
| 00:41 | In motorsport, it's a completely different story. |
| 00:44 | The priority is purely performance with a focus on maximising both lateral and longitudinal grip of the tyres, quick response to driver inputs, high tunability and an ability to control the chassis to optimise the aerodynamics. |
| 01:00 | Generally speaking, all the things that we try to maximise in motorsport have a detrimental effect on the design priorities of road cars. |
| 01:07 | And conversely you'll often hear people complaining about the suspension of a given road car when it's being used for some type of motorsport. |
| 01:16 | It's important to remember that the designer of that car was likely prioritising very different things to what we might be looking for. |
| 01:24 | It's generally not a case of a suspension being bad, it was simply intended for a different purpose. |
| 01:30 | In truth, the design of a well optimised suspension intended for road use, is a vastly more complex task than that of designing something for motorsport use only. |
| 01:40 | One thing we need to make clear for this course is that we'll be ignoring some of the effects of tyres while discussing motorsport suspension. |
| 01:47 | The reality is that in addition to the tyres being critical in their own right, they're also a part of a vehicle's suspension. |
| 01:55 | For example, each tyre has a vertical stiffness that makes it operate as both a spring and a damper which is fitted in series with the rest of the suspension. |
| 02:05 | While tyres will come up at some points through this course, their contribution to the suspension will be largely ignored for the sake of simplicity and discussing suspension fundamentals. |
| 02:15 | Before we get into the course material, I first want to introduce some terms and definitions that you'll need to understand as we move through. |
| 02:22 | Let's start with the very basics, lateral is a term that we use to describe the side to side direction of the car. |
| 02:29 | It's often used when we're discussing cornering where the tyres will be predominantly exerting a lateral force on the suspension. |
| 02:36 | Longitudinal is how we describe the forward and aft direction of the car. |
| 02:41 | We'll often use this term when discussing acceleration and braking where the tyres are predominantly producing longitudinal forces. |
| 02:48 | You're also going to be hearing the terms heave, roll and pitch. |
| 02:52 | Heave is used to describe the vertical movement of the chassis. |
| 02:55 | Roll is where the chassis rotates around its longitudinal axis and pitch is where the chassis rotates about its lateral axis. |
| 03:04 | Next the terms compression and jounce refer to the suspension and wheel moving upwards towards the chassis. |
| 03:10 | While rebound and droop refer to the suspension and wheel moving downwards away from the chassis. |
| 03:16 | Ride height is used to describe the height of the chassis above the ground plane. |
| 03:20 | Any convenient point of the chassis can be used as a reference point to define the ride height but generally 4 points will be chosen. |
| 03:28 | Two at the front and two at the rear. |
| 03:30 | Using 4 points allows us to easily measure the height and inclination of the chassis. |
| 03:36 | We'll also be using the term static and dynamic throughout the course. |
| 03:40 | In this context, static will be used for measurements or parameters when the car is at rest. |
| 03:45 | Generally sitting on a flat and level surface. |
| 03:49 | Dynamic will be used for measurements or parameters when the car is moving around the track which will be constantly changing. |
| 03:55 | The term kinematics is used to describe the motion of different parts of the suspension. |
| 04:00 | How each part moves and through which arcs. |
| 04:03 | And that's defined by the geometry and the pick up points. |
| 04:07 | The key thing here is that kinematics has nothing to do with any forces, only the motion. |
| 04:12 | You'll also be hearing the term stiction which is used to describe the friction that occurs in a sliding component. |
| 04:19 | Most often in the context of components like dampers. |
| 04:22 | The end effect is a friction that must first be overcome before the component will move. |
| 04:27 | This often occurs in dampers that are used in MacPherson struts where side load on the strut makes a stiction force in the damper that must first be overcome before it'll move. |
| 04:38 | Next, independence is a term that's used to describe one side of the suspension being able to move without directly affecting the movement of the other. |
| 04:46 | Different suspension layouts allow different levels of independence and this is an important property to consider because the level of independence has a large bearing on the ability of a suspension to maximise the time spent by each tyre on the road surface when it's rough. |
| 05:02 | You'll be hearing the term compliance quite a bit as we move through the upcoming modules. |
| 05:06 | This can be thought of as the deflection of components that we don't usually want to deflect. |
| 05:12 | Compliance is an important parameter in suspension and is generally considered a bad thing because it means our components are flexing under load. |
| 05:20 | And that results in things being in different positions and angles than we intended. |
| 05:24 | While it won't be relevant for this course, it's worth noting that in high level motorsport, compliance is intentionally designed into components to achieve different handling characteristics. |
| 05:34 | When we use the term steady state in the context of suspension, we're talking about the car being settled and running at a consistent state. |
| 05:42 | An example of steady state is when we're in a constant speed corner as we would be on a skid pad. |
| 05:48 | All the driver inputs are constant, that means things like the throttle, brake and steering angle are all constant over time. |
| 05:56 | The opposite of steady state is transient which means things are changing over time. |
| 06:02 | An example of something transient would be the state of a car when we're transitioning from acceleration to braking or the steering input on corner entry. |
| 06:11 | In these cases, the driver inputs are changing over time. |
| 06:15 | So in summary, the purpose of a motorsport suspension is to maximise the grip from our tyres, give us quick response to driver inputs, allow high tunability and help us maximise our aerodynamics. |
| 06:29 | The goals of a road car suspension are very different from what we want in a motorsport setup. |
| 06:34 | And it's helpful to have a good understanding of the commonly used terms and definitions used in the motorsport world. |
| 06:40 | Make sure you take a second look at this module if you feel like you need a clearer picture of what they all mean before moving through the rest of this course. |
