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Practical Corner Weighting: Adjusting Ride Height

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Adjusting Ride Height

03.49

00:00 - As we've discussed through the course so far, optimising your corner weight is going to require you to make adjustments to the car's ride height.
00:08 Before making any adjustments, you need to understand how the ride height will affect the operation of the suspension system.
00:14 One of the biggest concerns is maintaining enough suspension travel as lowering a car excessively can have the result of sitting the suspension on or very close to the bump stops.
00:26 The bump stops can be considered the suspension's last line of defence and they're there to prevent damage from your tyres, wheels or suspension arms physically contacting the chassis under full compression.
00:37 The problem is that when you run onto the bump stop, the effective spring rate at that corner of the car climbs sharply and this can cause a sudden loss of traction and unpredictable handling.
00:48 That's not to say that you should never allow the suspension to contact the bump stops and in particular the bump stops are used as a tuning tool for cars with very high down force.
00:58 However you do need to maintain sufficient suspension travel to allow the suspension to do its job first and also understand the implications if the suspension does contact the bump stops.
01:10 There are other fundamental issues with lowering a car excessively as well since the factory suspension geometry may now be less than desirable.
01:17 To illustrate this, let's take an example of a common MacPherson strut front suspension design.
01:24 It's quite common in a stock production car to find that the lower control arm is either parallel to the ground at stock ride height or potentially even angled downwards from the chassis mounting point towards the hub.
01:36 This promotes negative camber gain as the suspension compresses, which is exactly what we want.
01:42 On the other hand though, if we lower the car to a point where the angle between the lower control arm and the strut is greater than 90 degrees, now as the suspension moves into compression, we'll see the wheel move towards positive camber instead.
01:56 As a general rule, if the lower control arm is pointing upwards from the chassis towards the hub, then the geometry is less than ideal and the ride height may be too low.
02:07 We also need to consider the effect of lowering the car on the relationship between the roll centre and the centre of gravity which we covered in the previous modules.
02:16 Essentially, as the roll centre and centre of gravity get further apart, the roll moment increases and the car will tend to roll more in a corner which is something we don't want.
02:26 More body roll in a corner, coupled with a lower ride height that may potentially compromise suspension travel and bump is less than ideal.
02:34 Naturally as we'll see further through the course, there are aftermarket parts available that address some of these issues and in many purpose built racecars, significant design changes are made to the suspension geometry and mounting points in order to allow a low ride height without compromising the suspension operation.
02:52 The next question we need to consider is how to we measure ride height.
02:57 This is actually not as straightforward as it might sound as there are a wide variety of places we can make that measurement from which may include the sill panels, cross members or chassis rails.
03:08 In tightly controlled race classes which specify a minimum ride height, the rule book will tell you where the ride height must be measured, so you know exactly what to do.
03:18 If there is no specification, then it's really up to you and in reality it doesn't really matter where you're making your measurements from as long as you use the same point each time.
03:29 Common sense would dictate that you should use a rigid point on the car such as a sill or the chassis rail that's unlikely to move from one setup session to another.