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# Practical Corner Weighting: Roll Centre

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## Roll Centre

### 02.43

 00:00 - When you're behind the wheel of a racecar, we'll obviously be experiencing a level of G force while cornering, braking and accelerating. 00:07 These G forces result in the car rolling as we corner as well as diving under brakes and squatting during acceleration. 00:15 When we consider body roll in a corner, the point which the car pivots around is called its roll centre. 00:21 This is an imaginary point on the car that moves when we change things like ride height, wheel offset and suspension setup. 00:29 We therefore need to consider what suspension setup you are running as each different type creates a different roll centre. 00:36 In a MacPherson strut suspension design, we need to start by plotting the instant centre which we can find by drawing a line through the lower control arm pivot points. 00:45 Next we can draw a line perpendicular to the strut top and the instant centre is where these two lines intersect. 00:52 Once we've found the instant centres, we can then plot a line from each instant centre through the centre of the contact patch. 00:59 Where lines intersect is the roll centre. 01:03 In a double wishbone suspension system the roll centre can be found by drawing a line through the inner and outer pivot points of both the upper and lower wishbones. 01:12 Where these lines intersect is the instant centre and again we can plot lines from the instant centres to the centre of the tyre contact patch. 01:20 As with our MacPherson strut example, the place where these lines cross is the roll centre. 01:26 We've only looked at a simple drawing to describe the roll centre so far and it's important to understand that the roll centre isn't stationary but rather it moves around as the suspension compresses and extends and the car negotiates corners and bumps. 01:40 One of the design challenges that engineers go through is trying to maintain a stable roll centre to provide predictable handling. 01:48 When we make adjustments to our corner weights, we're most likely going to be adjusting the ride height of the car and this in turn can affect the roll centre location. 01:58 To understand the implications of this, we actually need to consider not just the affect on the roll centre but also the relationship between the roll centre and the centre of gravity which we'll cover in the next module. 02:10 Of course there are roll centre correction products available on the market for many cars which can address issues with roll centre height location, providing the ability to change the roll centre height to suit lowered ride heights. 02:23 Adjusting and optimising the roll centre height is a very large topic in and of itself and is beyond the scope of this course. 02:30 For our purposes, it's simply enough to understand the concept of roll centre height and the fact that we will affect this during the corner weighting process.

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