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Suspension Tuning & Optimization: Unsprung Mass Load Transfer

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Unsprung Mass Load Transfer

02.54

00:00 - Over the next 3 modules, we'll be discussing the 3 different contributions to lateral load transfer that exist before bringing them all together in the final module of this section to discuss how we use them to tune for balance.
00:12 The 3 different contributions to lateral load transfer as the unsprung mass, the elastic sprung mass and the geometric sprung mass.
00:21 In this module, we'll discuss the load transfer due to the unsprung mass only.
00:27 As you'll remember from the foundation concepts section of this course, the unsprung mass is everything that's not supported by the suspension springs.
00:35 In simple terms, this means the wheels, tyres, brakes, uprights, as well as part of the suspension arms and dampers which is what we see highlighted here.
00:45 We can simplify all these concepts down to being represented by a single mass for each corner of the car.
00:53 The position of this mass is located at the centre of gravity of the entire unsprung mass for that corner of the car.
01:01 The calculation for accurately finding this centre of mass for each of the unsprung masses can be quite involved.
01:07 A reasonable approximation for this in most cases is to assume the centre of mass is located at the geometric centre of each wheel.
01:16 When we're cornering, we have a lateral acceleration acting on each of these effective masses.
01:22 These lateral accelerations result in a lateral load transfer of their own and the magnitude of this load transfer for every corner of the car is defined by this equation.
01:31 To calculate the total contribution of unsprung mass to lateral load transfer, we sum up the 4 individual load transfers from each corner of the car.
01:40 What's unique about the unsprung mass load transfer in comparison to both the elastic and geometric sprung load transfer components that we'll be discussing in the following modules is that it's not a very practical thing to change in order to affect the load transfer.
01:56 While it is possible to change the amount of load transfer of the unsprung mass, this involves buying or building new components rather than simply making adjustments to the ones you have.
02:07 For example, if we wanted to reduce the non sprung mass load transfer, we'd typically be doing this with things like lighter weight wheels, brake discs and callipers or redesigned uprights.
02:17 We could physically lower the components like the brake callipers and the ducts as well.
02:23 Needless to say, these aren't the sorts of things that we'll be changing throughout a race weekend as they're essentially baked into the design of the car.
02:30 To summarise, the unsprung mass lateral load transfer is one of 3 lateral load transfer components we'll consider.
02:38 This load transfer comes from the height and position of our unsprung masses on each conrer of the car.
02:45 Changing the unsprung mass load transfer is not normally a practical tuning tool at the racetrack.