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# Suspension Tuning & Optimization: Suspension Geometry Introduction

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## Suspension Geometry Introduction

### 05.16

 00:00 - In this section of the course, we're going to look at some of the most important and useful aspects of suspension geometry. 00:07 This is going to give you a good grounding for later sections of the course. 00:11 Suspension geometry is a big topic but it's one that isn't all that difficult to get your head around. 00:18 Once you get an understanding of the terms used, and how it all works. 00:21 Let's start by looking at the bare fundamentals before we move into the more subtle aspects of the topic. 00:27 First, we should define what we mean when we use the term suspension geometry. 00:32 This describes the position and orientation of our suspension components and as we can see here in this case, a double wishbone, there are many ways we can arrange the different components. 00:42 Each variation of these can be thought of as having a different suspension geometry. 00:47 Starting from the chassis, the points where each of the arms and members attach to the chassis are usually referred to as the chassis pickup or hard points. 00:57 Each of these points will have a type of joint that locates the position of each suspension component which also allows it to rotate as the suspension moves through its travel. 01:07 The suspension arms, also known as the members are attached at one end to the chassis pick up points. 01:12 These might include upper and lower wishbones, suspension links in the case of a multi link or the upper part of the strut in a MacPherson strut. 01:21 The steering rack and links also form part of the suspension geometry. 01:24 The rack dictates the inner pivot point of the toe link with the toe link itself forming one of the suspension arms. 01:31 On the rear axle where you won't usually find a steering rack, the inner chassis pickup for the rear toe link will usually be fixed. 01:39 The upright is what houses the wheel bearings and gives the brake calliper a place to mount to. 01:43 This is also what each end of the suspension arm links will be attached to. 01:49 In the case of a MacPherson strut, the strut will be rigidly attached to the upright. 01:53 Each of the suspension arms and links will have its own pivot point on the upright in a similar way to the chassis pickup points. 02:01 Primarily it's the location of each of the pivot points in 3D space that we're most interested in when we discuss suspension geometry. 02:10 By modifying the position of these points we modify the geometry. 02:15 The way the angles and positions of each of the components, that's the wheels, uprights, suspension arms, dampers and springs, change as we move the suspension through its travel, is what we often refer to as the kinematics of the suspension. 02:30 So to make it really clear and simple, geometry describes the location of each point of interest in space while kinematics describes the path or arc each component follows as we move the suspension during operation. 02:44 This brings up an important aspect of suspension behaviour that needs to be clearly understood. 02:49 Almost all parts of the suspension move through an arc as it operates. 02:54 Rather than travelling along straight lines. 02:56 One of the only things that does move in a straight line is the damper as it compresses and extends. 03:03 Almost everything else, the uprights, suspension arms etc are all moving through arcs. 03:10 There's a lot of subtlety and complexity involved in suspension kinematics and we're not aiming to cover all of that within this course. 03:18 Instead, we're going to focus on the basic principles that will be of most use when tuning an existing suspension. 03:25 For clarity's sake, let's quickly discuss a couple of other factors that are important to at least be aware of before tackling suspension geometry any further. 03:34 Starting with compliance. 03:36 Which is essentially the flex that we see in all suspension parts as they cycle through their travel. 03:42 In professional motorsport, the compliance is calculated, measured and accounted for as part of the suspension design and setup. 03:49 But that's just not practical at the amateur and club level and we'll be ignoring it for our purposes. 03:55 This means that while things like our suspension arms, bushings and bearings, uprights, wheels and even the chassis itself aren't perfectly rigid, in our upcoming discussions we'll be treating them as though they are. 04:08 The other big element of suspension kinematics that we won't be discussing in detail in this fundamentals course is bump steer. 04:15 Put simply, this is the change in toe angle of a wheel as the suspension moves through its travel. 04:21 In the case of the front axle, this is with the steering wheel held straight ahead. 04:25 Bump steer occurs due to the combination of different arcs, the steering arms, control arms and upright travel through. 04:33 It's often thought of as a negative quality of the suspension but it's also used to modify the behaviour of the car intentionally. 04:40 If you'd like to know more, you can find an in depth description of the definition and measurement of bump steer in our motorsport wheel alignment fundamentals course. 04:49 To summarise, suspension geometry describes the position in space of our various pivot points for each part of the suspension whereas kinematics describes the resulting motion of each part of our suspension that is defined by our suspension geometry. 05:05 It's important to understand that it's only the strut itself that has a linear motion. 05:10 Everything else is travelling in an arc.

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