# Double Wishbone Suspension Spring Issue

Hello, I am trying to create a custom chassis that is using double wishbone suspension, but for some reason when I increase the spring damping, the suspension freaks out. This is most probably a geometrical issue and I have spent quite a lot of time trying to see where it fails at, but with no success.
Here is the model file for you to test it out: C-Chassis front suspension.rbxm (9.4 KB)

Either add another spring (if the visual of it doesnâ€™t matter) or set limits to the hinges in the wishbones so they canâ€™t move too far.

You may be overdamping your springs.

There is an equation to calculate how much force is needed to return a spring back to its free length without under or overshooting. The spring would be considered to be critically damped, as opposed to underdamped or overdamped (in your situation).

The formula to calculate how much damping force you would need to achieve this:

Critical Damping = 2 * SQRT(SpringStiffness * LoadOnSpring)

Where:
SpringStiffness = The stiffness value youâ€™ve set for your springConstraint, and
LoadOnSpring = The load on your spring.

In a a 4 wheeled vehicle, considering weight is being distributed evenly to all 4 wheels, the load on your spring will be equal to the vehicleâ€™s (unsprung mass/4) * + the mass of one wheel.

However, your car most likely has some sort of imbalance due to seat placement, heavier front end, etc. You can use the CenterOfMass property on your vehicleâ€™s rootPart and the length of your vehicleâ€™s wheelbase to calculate the % weight distribution or weight bias on your front and rear axles, which will give you a better picture of the load on each spring.

The goal is dampen your suspension somewhere between 0 and its critical damping value.

*all of your vehicleâ€™s mass excluding the wheels or anything else connected to your wheels)

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apologies for reviving this year old topic, slight typo: load on spring is equal to the vehicleâ€™s sprung mass, not unsprung mass.

the sprung mass is all your vehicleâ€™s mass excluding wheels and any suspension parts directly welded to them
unsprung mass is the wheels + those suspension parts directly welded to the wheels

so if your car has a total mass of 100, and each corner wheel assembly is mass of 10, then your unsprung mass is 40 (4 wheels) and sprung mass is 60

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