I am trying to create a simulation for car suspension and tyre physics and to do the tyre physics I need to know how much weight is over the friction point that is under the spring.
The force associated with springs is well described by Hooke's law. The spring force is given by, $$ F = k x $$ where $F$ is the spring force, $x$ is the displacement of the spring from its original resting position, and $k$ is the spring constant in units of force per length.
The weight supported by each spring will depend on how the weight is distributed by the vehicle. Most vehicles are slightly heavier at the front so, a 60:40% or 55:45% distribution would be a good approximation for most cars. Sports cars get closer to an even split. Then, you would subtract the weight of the tyre and supporting axle, brake, etc. since that weight is not supported by the spring.