If you’re a motorsport fan, you’ve probably heard the terms “sprung mass” and “unsprung mass” before. But what do they actually mean? In this blog post, we’ll discuss what sprung and unsprung mass are, and how they affect cars in motorsport.
The idea of sprung and unsprung mass is crucial to discuss early on in this course since we’ll come back to it often. The chassis, anything firmly connected to it, can be described as the sprung mass. Engine, petrol tank, driver, body panels, etc. Everything that relies on suspension springs for support.
The unsprung mass is essentially everything else. The wheels, tires, brakes, and suspension are all part of the equation. To be more specific, certain elements of the suspension are connected to both the sprung and unsprung masses. Take the suspension arms for example. They’re partially sprung and completely unsprung since they’re linked to both the entirely compressed and entirely unconstrained masses. But this is only theoretical.
In practical terms, It’s obvious that we want to minimise the overall mass of our vehicle in order to improve its performance. But the key differences between sprung and unsprung mass are important to understand.
The sprung mass refers to the dead weight we have to carry around as we move. The unsprung mass has a direct effect on how well our suspension can follow bumps in a road surface. It’s important to keep this distinction in mind as we continue through the course.
A fundamental principle of physics is that F=MA, meaning that force is equal to mass multiplied by acceleration. The higher the mass, the higher the forces required to accelerate it. As a result, reducing the weight of your vehicle in the presence of all other variables being equal makes sense.
The suspension deals with our tyres remaining in touch with the road to maximize grip, and the more unsprung mass there is, the harder it is to minimize tyre contact patch variation of vertical load. As a component moves at a certain speed, its heavier weight has greater kinetic energy.
In conclusion, the greater unsprung mass we have, the worse our suspension will perform on uneven and undulating terrains. As a result of this, there will be more compromises and consequences, as well as a lower quality surface to run on, which will be far more harmful to the vehicle’s performance.
Lower unsprung mass, on the other hand, has a negative effect on suspension compliance. If we reduce the size of components to reduce weight, we’ll also enhance compliance or how much they flex. Compliance in suspension components increases as we decrease component size to lower unsprung mass. The main disadvantage of reduced unsprung mass is that it causes more wear and tear on the suspension system.
We can improve the design of the components or use special materials to reduce the trade-off, but both come with a big increase in manufacturing time and cost.
Another important thing to consider with unsprung mass is its contribution to lateral load transfer. The larger our unsprung mass and the centre of gravity height of that mass, the more load transfer will occur.
To sum up, sprung mass can be thought of as the chassis and everything else attached to it securely. Unsprung mass is made up of the wheels, tires, brakes and some aspects of the suspension. We want unsprung mass to be minimized so we can maximize grip ,but it’s crucial to understand that diminishing unsprung weight comes at a cost including added expense and decreased stability.
