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Suspension Tuning & Optimization: Purpose of Dampers

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Purpose of Dampers

07.28

00:00 - Dampers, otherwise known as shock absorbers, are among the most misunderstood parts of the suspension system.
00:06 The confusion starts straight away with the term shock absorber.
00:09 Dampers don't absorb shocks, they damp.
00:12 Which in the context of suspension means their primary purpose is to reduce oscillations in the suspension.
00:19 In their simplest form, dampers convert kinetic energy into heat that would otherwise cause the springs and anti roll bars to continue oscillating.
00:28 Before we jump into this topic, I need to be clear, damping is an enormous and complex field, we could easily have a dedicated course to just the basics of damping.
00:38 Let alone advanced tuning.
00:40 So in this suspension fundamentals course, the aim is instead to give a practical introduction to the topic along with some tools to help you start making changes to your damping to improve your car.
00:52 If you've ever owned an old car with worn out dampers, you might be familiar with the sensation of the car bouncing up and down like a boat after it hits a bump.
01:00 This is a perfect illustration of what an almost complete lack of damping actually feel like.
01:06 In the earlier springs section, we discussed about the case of the suspension without any damping oscillating forever.
01:13 While that's true in theory, in reality, this oscillation would also be damped out and absorbed by other losses in the suspension aside from just the dampers themselves.
01:23 This includes polymer suspension bushings, tyres and even the springs themselves to some degree.
01:29 However, the vast majority of the damping in the suspension does come from the dampers and that's what we'll be discussing in this section as that's the part of the car we'll usually have available to tune.
01:39 Let's take the case of a car with very little damping at all.
01:42 If we apply a force to the front of the car, and then let it go, plotting the front ride height over time, we can see that the suspension continues to oscillate for some time before the oscillations die down.
01:55 If we perform the same test again but increase the front damping by adjusting the damper, we can see that the oscillations decay more quickly.
02:03 If we make yet another increase in the front damping, the oscillations die out even sooner again.
02:10 If we continue to add damping to the front axle, there'll be a point at which when we release the car, it does not oscillate at all in fact there's so much damping that the car is actually now rising up again quite slowly and never actually overshooting the static ride height at all.
02:26 The source of these oscillations we're trying to hard to damp out are bumps or irregularities in the road as well as from driver inputs.
02:33 Braking, accelerating and steering.
02:36 The energy from these sources is transferred to the springs and then released.
02:40 We're using the damping to control the release of this energy from the springs.
02:45 By damping out the movement of the suspension we aim to keep the tyres more in contact with the road, reduce the variation in vertical load on the tyres and keep the suspension travel within sensible bounds which helps keep things like camber and toe within the range we want, to reduce the overall movement of the sprung mass.
03:04 When we have too much damping, the tyres will no longer be able to follow the surface of the road well because the suspension will act as if it has too much stiffness which results in the variation of vertical load on the tyres increasing and overall, that reduces our grip.
03:19 For a given road profile and spring stiffness, there's an optimum level of damping to maximise our grip.
03:26 In practice, this means each spring stiffness has a different optimum damping setting for each venue we run at.
03:33 At this point, it's worth explaining what I mean by vertical load variation on the tyres.
03:39 In simple terms, the minimum vertical load we apply to each tyre throughout any section of a course is going to be the limiting factor for our longitudinal and lateral accelerations.
03:49 High grip tyres and a lot of downforce are negated by variation in the vertical load applied to the tyres.
03:57 As we see in this example, where the vertical load applied to a given tyre is varying over time, the main shape of the variation of the vertical load profile is from load transfer throughout the lap as well as downforce which is indicated by this line.
04:12 However, zooming into one section of track, we can see these higher frequency changes in vertical load more clearly.
04:18 These are mainly due to the uneven profile of the road surface and the suspension's response to these unsteady inputs.
04:25 Part of these higher frequency force changes come from the energy being stored and released within the springs.
04:31 Tracing a line through the points of minimum force, shows us the limiting factor for grip.
04:35 These other areas of high vertical load can't be fully exploited because of the minimums we see here.
04:43 The important point to take away here is that if we have a high force potential we're limited by these transient points of minimum load.
04:51 THese are what's limiting our performance and preventing us from exploiting the full theoretical performance envelope of the car.
04:59 We use dampers to tune the response of each corner of the suspension to try and even out the load variation as much as possible.
05:05 Reducing these minimums is what will gain us grip overall.
05:08 A secondary purpose of dampers is to change the rate of suspension movement.
05:12 This gives us some control over how quickly the front dives under braking or the rear squats under power.
05:19 We can also use them to influence how quickly one end of the chassis rolls as we enter and exit each corner compared to the other.
05:27 We can think of dampers as giving us control over how fast something moves, not how far something moves.
05:33 When we boil it right down, if we want to control how far one corner of the car deflects to a given load, we do that with tools like springs, anti roll bars and bump stops.
05:43 If we want to change the rate at which that movement happens, we use the dampers.
05:47 Dampers are also ley to controlling the transient pitch, roll and ride height of the sprung mass for aerodynamic reasons.
05:56 As we discussed in the last section, in the case where we have a car with a powerful underfloor, it becomes important to control the movement of the sprung mass so that it stays within certain limits.
06:06 This means that if we gave the chassis and suspension enough time, they would settle to an arbitrary final position but how long it takes to settle there would be affected by our damping.
06:16 The closest we can get to steady state in real life is by running the car at constant speed on a skid pad.
06:23 In reality, there are very few times a car is running close to steady state in competition.
06:28 We instead spend the majority of our time transitioning from one state to another.
06:33 This is why damping can be such an influential tuning tool as it controls the transience so we can make use of damping to control the floor, to keep it within its required limits, though it's important to understand that the amount of damping usually required to control your sprung mass in this way will come at the expense of reducing mechanical grip.
06:52 The type of car and configuration of the circuit will determine which of these we decide to prioritise.
06:58 To summarise this module, dampers are used to control the rate of deflection, not the magnitude.
07:04 This helps reduce the oscillation of the suspension, controls the rate of compression and rebound of each corner of the car and keeps the floor of the car within its intended limits.
07:14 There's an optimum level of damping for each car and road surface combination.