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Suspension Tuning & Optimization: Basic Damper Tuning

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Basic Damper Tuning

08.54

00:00 - Now that we have a clear understanding of exactly what dampers are and how they work, let's take a look at how they can be tuned and the basic tools we use to make that happen.
00:10 External adjusters are the quick and easy option that allows us to change the damping behaviour but we can also disassemble the dampers to modify their valving which can apply to both the needle geometry in size as well as the shim stack configuration.
00:24 We're also able to change the viscosity of the hydraulic fluid and to some extent the pressure of the nitrogen gas.
00:31 To get a better understanding of how we make use of these adjustments, let's start by looking at how each area of the damping plot we introduced in the previous module, typically relates to different handling characterisitcs of the car.
00:43 We can do this by breaking down the different velocity ranges into different handling regimes to understand a little more about what they mean.
00:52 This is a broad general discussion relevant to most road racing situations for something like a club racing saloon, touring or GT car but the principles apply to any 4 wheeled racing vehicles. We can use the following damper velocity boundaries to help us focus on the relevant parts of a damper force plot.
01:10 Depending on what behaviours of the car we're looking to change.
01:13 The 0-5 mm/s range highlighted here is where the friction forces both inside the damper and within the rest of the suspension tend to dominate.
01:24 Generally the behaviour in this speed range is governed more by the components we use in the suspension like the amount of friction and spherical bearings, the seals and the internal gas pressure in the damper rather than any adjustment we make to the dampers.
01:38 The 5-25 mm/s range highlighted here is a speed range we're typically tuning to control the transient corner entry and exit balance.
01:47 As well as the heave, pitch and roll movements of the sprung mass.
01:51 In other words, we're influencing the transient vertical load on each tyre during driver inputs as well as the motion of the chassis.
01:59 This is the range that's considered low speed and changes made here tend to have the most influence on chassis movement.
02:06 So when you're tuning for underfloor aerodynamics, this is what you're often concentrating on.
02:11 In the case we have a set of dampers that has only low speed adjustment, this is the speed range we can expect the adjusters to have the most influence.
02:19 The 25-200 mm/s range highlighted here is largely the result of bumps and irregularities in the road surface.
02:27 This is the range we'd normally consider high speed and it's where we're tuning to change the car's behaviour over bumps and rough surfaces like street circuits or a rally stage.
02:38 At a particularly smooth racetrack, we wouldn't expect to see the dampers spend much time in this speed region at all.
02:45 In the case where we have dampers with high speed adjustment, this is the speed range over which we can expect them to have the most influence.
02:52 At 200 mm/s and greater, we're looking at a range where the damper is subject to violent speeds and accelerations like hidden curbs in a circuit car or landing a jump in an offroad vehicle or rally car.
03:04 This is the range at which a blow off adjuster will usually start being effective.
03:08 We can use blow off settings to help the car deal with these big hits better by reducing the damper force at extremely high velocities which allows the unsprung mass to ride the curb without upsetting the sprung mass as much.
03:21 Keep in mind that all of the velocity ranges we've just discussed are approximate and to be used as a rough guide only.
03:29 The design and valving used by each damper manufacturer as well as the motion ratios and demands of the exact type of competition you're part of, may require modified boundaries to be used.
03:40 But what we're looking at here is a sensible starting point.
03:43 The majority of people racing at an amateur or club level will be using dampers that likely only have a single external adjustment if any.
03:51 As we learned in the previous module, this will most likely primarily be a low speed rebound adjuster.
03:59 On the upside, if you could only choose one adjustment type, in many cases, this would be it.
04:04 That's because it's one of the most powerful damper tuning tools we have to effect not just the mechanical but also the aerodynamic grip.
04:11 Low speed rebound has a large influence over the control of the unsprung mass as the tyre negotiates irregularities in the road surface.
04:18 And that consequently means it plays a significant role in maximising the amount of time the tyre spends in contact with the ground as well as affecting the contact patch load variation which is one of the most important things to reduce in the case of a mechanically biased setup.
04:34 Low speed rebound is also most dominant in controlling the average position of the sprung mass for aerodynamic reasons.
04:41 Helping to reduce the transient fluctuations in the underfloor height and orientation to maintain a consistent downforce.
04:49 With this being a fundamentals course, the intent isn't to cover all aspects of damper tuning so with that in mind, we're going to limit further discussion of damper tuning to single adjustable dampers which we'll cover with a dedicated module in the upcoming practical skills section.
05:04 One important aspect we haven't addressed yet is selecting the right damper for a given car.
05:09 The truth is, this is something well and truly outside the scope of this course because it would require us to spend a whole lot more time buried in the heavy theory side of things.
05:18 So in an effort to put a long story short, damping specifications are calculated based on the magnitude of the sprung mass, the spring stiffness we're using and the intended application.
05:29 From there, we can use something called the damping ratio to specify the required damping and get ourselves in the ballpark.
05:37 The shape and nuance of the damping force curve that we see here also needs to be specified.
05:41 These are determined through a mixture of simulation, real world testing and experience.
05:46 The good news is that most of this work is usually done for you if you're buying a set of dampers specifically for your make and model of car.
05:55 This way the approximate mass, motion ratios and spring rates, if you're using the springs supplied will have already been considered in the specification of the damping behaviour.
06:04 Of course you will need to discuss your intended application of the car with your damper supplier ahead of time.
06:10 This also means that if you end up fitting springs of a significantly different rate to those that the damping behaviour was designed for, you may not have sufficient adjustment range to keep the damping behaviour suitable.
06:22 In this case, you may need to have your dampers revalved or purchase an entirely new set.
06:28 In the case where you're building a car from scratch, where you're a long way away from the original suspension layout of the car, or you've fitted springs of a significantly different rate, it's best to consult with a damper manufacturer or supplier to get them to specify suitable damping behaviour.
06:44 Dampers really are one of those components where you get what you pay for.
06:48 The tolerances involved in the internals to achieve reliable and consistent performance are extremely fine and this naturally pushes up the manufacture and servicing costs.
06:58 The after sales support and advice you'll get from a high quality manufacturer or their agent is also worth considering as part of your purchasing decision.
07:07 Another thing to consider as part of damper tuning is regular servicing.
07:11 As we mentioned earlier in the course, the hydraulic fluid deteriorates over time and this leads to changes in damper performance.
07:18 The mechanical behaviour of the shim stacks and needle valve also needs attention as time goes on.
07:24 For a competition car you should have your dampers serviced at a minimum of at least once per season.
07:29 Depending on how much mileage you're doing.
07:32 In professional racing, dampers are inspected, tested and often serviced after every race meeting at significant expense which shows you the importance of the conditions of the internals.
07:42 Now that we have a broad understanding of the basic practicalities and tuning philosophies involved in motorsport damping, we'll leave the application of this theory to the practical skills section later in the course where we'll look at some real world examples.
07:56 In addition to the practical skills section, our professional motorsport data analysis course will also be of interest to anyone looking to make use of data acquisition as part of their suspension and damper tuning process.
08:07 In this course, the practicalities, set up and analysis of damper potentiometers is covered in detail.
08:14 Summarising this module, we can use some well understood damper velocity boundaries to help us understand which part of a damper force curve we should be looking to influence depending on which aspects of our car's handling we're tuning.
08:27 Low speed rebound adjustment is one of the most powerful damping tools you're likely to make use of while you're tuning your suspension, particularly when starting out.
08:36 Specifying dampers for your car is best done with the help fo an experienced professional if you aren't able to purchase something off the shelf that's designed for your application.