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Suspension Tuning & Optimization: Pitch Center and Axis

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Pitch Center and Axis


00:00 - The pitch centre is a very similar concept to the roll centre.
00:03 The difference being that we're looking at the car in side view rather than in front view.
00:08 The pitch centre is of interest to us when we're looking at longitudinal performance which means braking and acceleration.
00:15 The pitch centre is the instantaneous point around which the chassis rotates in pitch.
00:20 Its construction is the same as that of the roll centre in that we make use of the front and rear instant centres in side view.
00:28 As you can probably guess, we project a line from the centre of each tyre contact patch to the instant centre of each axle.
00:37 The intersection of these lines defines the pitch centre of the sprung mass.
00:41 One important thing that differentiates the construction and behaviour of the pitch centre when compared to the roll centre is that because the front and rear suspensions won't generally have symmetry about the centre of the wheel base, the pitch centre won't usually begin or stay in the centre of the car as the chassis heaves which is what we see here.
01:02 As we modify the position of our suspension pickup points, we can affect the instant centres of each axle and therefore the position and behaviour of the pitch centre.
01:11 The positions of the pitch centre will impact how much the front and rear suspensions compress or extend under braking or acceleration.
01:19 And that means that by changing the position of the pitch centre, we can influence how the car behaves in these states.
01:26 The pitch axis is defined as the line that connects the two pitch centres as we have a pitch centre for both the left and right sides of the car respectively.
01:35 This is the axis about which the entire sprung mass will pitch around when we're braking or accelerating.
01:42 When the chassis moves in pure pitch or heave, the pitch axis stays aligned with the lateral axis of the car.
01:48 As it rolls though, it'll skew relative to the lateral axis, inducing more roll behaviour due to any pitching under acceleration or braking.
01:57 In summary the pitch centre is a similar concept to the roll centre but instead, applies to braking and acceleration as opposed to cornering.
02:06 We construct the pitch centre individually for each side of the car in side view.
02:11 When we move to a 3D perspective, we can expand the concept of pitch centre to a pitch axis.

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