Suspension Tuning & Optimization: Balance, Stability, Control and Grip
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Balance, Stability, Control and Grip
05.27
| 00:00 | - While this isn't a vehicle dynamics course, we can rarely talk about motorsport suspension without having an understanding of some of the basic concepts behind it. |
| 00:08 | Put simply, vehicle dynamics is a study of how a car responds to inputs from the driver, the road surface, and aerodynamics as it negotiates a given path. |
| 00:18 | When discussing suspension, we can use vehicle dynamics metrics to judge and measure the performance and behaviour of the vehicle. |
| 00:25 | These can either be subjective or objective. |
| 00:28 | In this module, we'll introduce these metrics so we can make use of them throughout the course as we progress. |
| 00:34 | There are a number of different and more in depth definitions for each of the terms in this module but I've tried to stick to simple, useful and practical explanations only. |
| 00:43 | Let's start with something we probably all have a fairly good understanding of, grip. |
| 00:48 | This simply refers to the forces our tyres can produce. |
| 00:52 | The grip we generate between the tyres and the road surface, is the primary metric we're interested in maximising when it comes to optimising our suspension performance. |
| 01:02 | Balance is also a commonly used term when discussing vehicle handling. |
| 01:06 | When balance is talked about in this context, it's referring to whether a car is oversteering or understeering. |
| 01:13 | In simple terms, a car that's understeering through a corner, will follow a wider path than is intended by the driver. |
| 01:19 | This is often referred to as push because it can feel like the car is pushing itself towards the outside of the turn. |
| 01:26 | Oversteer on the other hand is what we have when the car over rotates and takes a tighter path than the driver intends. |
| 01:33 | This is often referred to as the car being loose as it can feel like the rear of the car is loose. |
| 01:38 | When in a turn, a car will understeer if the front tyres are the limiting factor and it'll oversteer if the rear tyres are the limiting factor. |
| 01:46 | This means that we must have sufficient grip at each end. |
| 01:49 | Having a large amount of grip at one end is useless unless we can get sufficient grip at the other end to maintain balance. |
| 01:56 | It's also important to understand that understeer is fundamentally a stable condition. |
| 02:01 | Which makes it a safer handling trait relative to oversteer. |
| 02:05 | Which is fundamentally unstable. |
| 02:07 | We can think of it like this, when understeer occurs, if the driver doesn't react, the car will continue on a similar path. |
| 02:14 | If the driver doesn't react when oversteer occurs on the other hand, the car will most likely spin. |
| 02:20 | Oversteer requires fast and accurate inputs from the driver, typically in the form of opposite lock steering and throttle input to maintain control of the car. |
| 02:28 | Road car manufacturers will typically set up their suspension such that the limiting factor is understeer which keeps the limit handling predictable and safe for the average driver. |
| 02:39 | In motorsport, this bias is more down towards driver preference and event type. |
| 02:44 | In a circuit racing environment, we typically target a small amount of limit understeer. |
| 02:49 | Though this can change for different session types, A race versus a qualifying session for example. |
| 02:55 | Stability is another fairly self explanatory term that we'll see often. |
| 02:59 | But let's look a little deeper into what it actually means within the context of motorsport suspension. |
| 03:06 | At its most basic, stability describes the tendency of the car to remain on the current trajectory when subjected to a disturbance. |
| 03:14 | An unstable car will need a lot of driver input to keep it on the intended path. |
| 03:19 | A lack of stability is seldom good but one area where we're going to see a really big impact on lap time is at corner entry. |
| 03:26 | A car that's unstable in the braking zone and corner entry will limit the speed and brake aggression that can be used by the driver. |
| 03:33 | Some drivers are more tolerant to low stability than others. |
| 03:36 | And in some cases, it can actually be a good thing to reduce the stability of a car as it'll tend to help an understeering car rotate. |
| 03:43 | But again this is driver and session type dependent. |
| 03:47 | For example we're more likely to target a lower stability setup for qualifying where we want ultimate lap times however for a race, our lack of stability will be harder to manage over a full race and will also be harder on the tyres. |
| 04:00 | A lack of stability can be caused by many things but the most common culprits are erratic or unsteady driver inputs, a mismatch in grip between the tyres, incorrect brake bias, poor suspension kinematics, incorrect suspension stiffness balance, bumps in the road or an unsuitable downforce distribution. |
| 04:20 | The last useful metric we need to look at is control. |
| 04:23 | This describes the amount of authority the driver has over the vehicle to change the direction or path. |
| 04:29 | A vehicle with a lot of control will have crisp and direct response to steering inputs whereas a car with a lack of control will tend to be sloppy to respond. |
| 04:39 | Having higher level of control may be appropriate in competitions where many quick direction changes take place. |
| 04:44 | Or we need to be able to dart between traffic as we make our way around a lap. |
| 04:49 | It's not so much that we ever target a setup with less control, it's more that we'll end up reducing some control authority through making a setup change to improve another aspect of our handling. |
| 05:01 | Like increasing stability for example. |
| 05:03 | In summary, the metrics of grip, balance, stability and control give us a language and a template for describing and characterising the response of the vehicle we're tuning. |
| 05:13 | So while they're all words that you're no doubt familiar with already, it's important that you have a clear understanding of what they describe within the context of motorsport and vehicle dynamics. |
