So what does this mean in practice? High roll centres leave less weight to be transferred via the springs and vice versa. This weight transfer is resisted by the springs, anti-roll bars and dampers. Therefore the sprung mass weight transfer is based on a mass whose centre is the centre of gravity of the entire sprung mass, the mean roll centres and mean track. Via the sprung mass - The chassis is a rigid(ish!) structure which rolls around an axis between the front and rear roll centres. So a ride height adjustment to your race car, or a roll centre geometry change is a very valid tuning device. It can be varied simply by raising or lowering the roll centre relative to the ground. Via the roll centres - In this instance weight transfer is separate for front and rear. Ignoring unsprung weight transfer to simplify the discussion, weight can move: A certain amount of the weight transfer occurs as the forces generated by the cornering feed directly through the suspension links to the tyres. We need to recognise that not all the weight transfer goes via the springs, dampers and anti-roll bars. Weight transfer is affected by the distance between the CG Height and the roll centre. The Fig 1. below shows a MacPherson Strut Geometric roll centre: The Geometric Roll Centre location is what we will discuss here (if you are finding this bit interesting also try Google searching for “Force Based Roll Centre” which is the latest development of this which takes into consideration the dynamics of the roll centre). This discussion will identify the basics so that they can be considered in your project. What we need to take into account is the vehicles roll centre – both front and rear which together make the roll couple.ĭiscussion of roll centres in depth would take a long time and there are many good texts available should you wish to research further. Unfortunately this simplistic approach does not take account of complicated dynamics of a vehicle rounding a corner. This was then developed when we discussed roll stiffness which demonstrated how even with unfavourable weight distribution outright G-Force levels could match a vehicle with “perfect “ 50/50 distribution. The proportion of weight transfer the front and rear tyres experienced was assumed to vary depending on the static weight split of the car. When we first considered the weight transfer that the vehicle experiences around the corner a very simplistic approach was taken assuming a fixed level of centripetal force. Reduction in aerodynamic lift (assuming rake is maintained front to rear)Īs we already found in the weight transfer section that corner speed is a function of track width, weight and CG Height then surely it stands to reason that the more you lower the car the faster it will be able to round the corner? If you know what you are looking for, you will see the difference between a track car and a show car.įirstly lets look at the advantages lowering will always give us: “Slamming” or “Dumping” their “Ride” is the primary objective and many consider the lower the better. Many seem to view the fitting of suspension as merely a way to get the arch to tyre gap as small as possible. All too often you will see a car that has had literally tens of thousands of pounds spent on a high-power engine and braking set up, only to find that the suspension received a fraction of the budget and is often seen as an inconvenience. There is no doubt in the world of Aftermarket Tuning and Club Motorsport, that suspension geometry is one of the most overlooked factors. Including Lowering, Roll Centres, Bump & Roll Steer, Camber & Caster
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