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Practical Corner Weighting: Centre of Gravity

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Centre of Gravity

03.55

00:00 - One of the ways of adjusting the corner weight of your car is to physically move components such as the battery or fuel tank around the car in order to move their weight.
00:08 Of course, what we can achieve here might be a little limited in a production car, however if you're building something from the ground up, you may have a reasonable amount of freedom to select where key components are going to be mounted.
00:20 When doing this, it's a great opportunity to consider the centre of gravity for our car.
00:25 The definition of the centre of gravity is the point through which the entire weight of a body acts.
00:31 In plain English, it could be thought of as an imaginary point about which the car would balance if we were to support it at this point.
00:38 The rule for almost any type of motorsport is that the lower to the ground the centre of gravity is, the better the car will handle.
00:45 It's not just the centre of gravity that's important here but also how the mass of the car is distributed relative to the centre of gravity.
00:54 This is referred to as the polar moment of inertia which sounds complicated however what it means is that the closer we can keep the mass of the car to the car's centreline, the quicker the car will be able to rotate as we turn into a corner.
01:08 With this in mind, we really want any heavy mass located low down and close to the car's centreline, although this may not always be possible so some compromise may be necessary.
01:19 To demonstrate how a low centre of gravity helps us, let's combine the centre of gravity with the roll centre that we discussed in the last module.
01:27 You'll recall that the roll centre is a point in space about which the car will roll as it goes through the corner.
01:33 All other things being equal, the amount it will roll will depend on the distance between the roll centre and the centre of gravity.
01:40 This distance forms a lever arm and the longer this arm is, the more effective leverage the cornering force has to cause the car to body roll.
01:49 Let's look at two examples to illustrate this.
01:52 In the first example, we have a high centre of gravity which creates a large lever arm to the roll centre.
01:59 When the car corners it will create a lot of body roll.
02:01 If we now take the same car and lower the centre of gravity, we can see that the length of the lever arm is now reduced which means that the car won't roll as much when the same cornering force is applied.
02:13 Measuring the height of the centre of gravity is reasonably difficult to do but we can calculate it using a bit of work and some maths.
02:20 Fortunately for the sake of corner weighting, we won't need to know exactly where the centre of gravity is located and instead there are some basic principles we can follow when it comes to moving weight around within the chassis.
02:33 The two key elements here are to make sure that any weight that is added or moved around the chassis is kept as low as possible and as discussed, this weight should also be kept as close to the centreline of the car as possible.
02:47 With this in mind, adding weight to the extremities of the car would be our last resort and where possible, weight should be added within the passenger compartment and as close to the floor as we can get.
02:58 If you're competing in a motorsport championship then often there will be a minimum weight limit and this may require you to add ballast in order to race legally.
03:06 This would be a great opportunity to use your ballast to help with corner weighting while not adversely affecting your centre of gravity.
03:13 Ballast can come in a number of shapes and sizes and lead tiles and gym weights are great examples of a sensible way of adding additional ballast to your car.
03:22 Not only do we want to consider where the ballast is added, but it's also important to make sure it's securely attached as the last thing we want is a ballast weight coming loose in the cockpit as needless to say, this could be incredibly dangerous.
03:36 If you're looking to better your lap times and don't have to worry about a weight limit, then I wouldn't recommend adding any extra weight to the car.