It depends... typically if you don't know what you are doing - changing these values will make the vehicle explode into a spike-ball of game crashing instabilities. From the wiki beamSpring: Spring of the beam. How much a beam will change length when a force is applied (N/m). Analogous to terms such as stiffness, rigidity, or modulus. beamDamp: Damp of the beam. How much energy is dissipated as a beam changes length (N/m/s). Damping causes vibration in the beam to fade out over time.
How much a beam will change length when a force is applied? What forces? Im still confused. So do I increase for desired effects?
What is the desired effect? Think of beams as rubberbands: "spring" is "rigidity", more or less, or how tense the beam between two nodes is. Higher values make beams more rigid, but also more prone to snap and vibration.
My desired effect is to make my hood of the car not vibrate due to weight. How do I counter this while able to keep the weight of the hood?
Increasing both might help, but it all depends on the source of vibration. If the main structure of the hood vibrates because the beams are flimsy, higher Spring could help. If vibration is being transmitted by other parts moving/undamped parts, it wont do anything.