Setting up a solid roblox spring constraint script suspension is usually the first big hurdle you'll hit when trying to make a vehicle that actually feels good to drive. If you've spent any time in Studio, you know the default physics can be a bit unpredictable. One minute you're cruising along, and the next, your car is doing backflips because it hit a pebble. That's where the SpringConstraint comes in. It's a powerful tool, but if you don't know how to script it and tune it properly, you're going to end up with a pogo stick on wheels.
Why Spring Constraints are the way to go
In the old days of Roblox dev, people used to hack together suspensions using all sorts of weird body movers or just sheer luck. Now, we have actual physics constraints. Using a SpringConstraint is the gold standard because it handles the math for you—mostly. It simulates a coil spring between two points.
When you combine these constraints with a bit of scripting, you get a vehicle that reacts to the terrain. It's not just about looking cool, though that's a big part of it. It's about weight transfer. When you hit the brakes, the front should dip. When you turn, the body should roll. If your suspension is just a static part, your car is going to feel like a cardboard box.
Setting up the physical bits first
Before you even touch a script, you have to get the physical hierarchy right. You can't just slap a spring on a wheel and hope for the best. Usually, you're looking at a setup that involves a PrismaticConstraint and a SpringConstraint working in tandem.
The PrismaticConstraint acts like the sliding rail—it keeps the wheel moving only up and down (or along whatever axis you choose). The SpringConstraint provides the actual "push" that keeps the car off the ground. You'll need two Attachments for the spring: one on the car's chassis and one on the wheel hub or the axle.
One thing I see a lot of people mess up is the alignment of these attachments. If they aren't lined up vertically, your spring is going to be fighting against the prismatic constraint, and you'll get a lot of jittering. Make sure your Attachment0 and Attachment1 are perfectly aligned on the X and Z axes so the spring only has to worry about the Y-axis (the height).
Tuning the properties in your script
This is where the roblox spring constraint script suspension really comes to life. You could manually set the properties in the Properties window, but if you want different car setups or upgrades, you need to do this via script.
There are three main variables you'll be messing with: Stiffness, Damping, and FreeLength.
The Stiffness factor
Think of Stiffness as how "hard" the spring is. If it's too low, your car will just bottom out and scrape the floor. If it's too high, the car will be incredibly bouncy and might even vibrate itself into pieces. A good rule of thumb is to calculate the weight of your car (the mass of all parts multiplied by gravity) and divide that by the number of wheels. That gives you a starting point for how much force each spring needs to exert just to hold the car up.
The magic of Damping
Honestly, Damping is the most important part that people overlook. If stiffness is the "push," damping is the "brake" for that push. Without damping, your car will bounce forever after hitting a single bump. Damping absorbs the energy. You want just enough damping so that when the car hits a bump, it moves up, comes back down, and settles almost immediately. If it oscillates more than once or twice, your damping is too low.
Adjusting FreeLength
FreeLength is basically how long the spring is when no force is acting on it. This determines your ride height. In your script, you might want to change this dynamically. For example, if you're making a lowrider or a truck with adjustable suspension, you'd just tweak the FreeLength property of all your SpringConstraints at once.
Writing the actual suspension script
You don't need a 500-line script to get this working. A simple LocalScript or a ServerScript (depending on how you're handling vehicle ownership) can manage the initialization.
You'll want to loop through all the wheels in your vehicle model. For each wheel, find the SpringConstraint and set its values. It looks something like this in your head: you grab the mass of the vehicle, do a little bit of math to find a "balanced" stiffness, and then apply it.
Pro tip: Don't hardcode your values. Use attributes on the vehicle model. That way, you can tweak the "Stiffness" attribute in the editor while playtesting, and your script can just read that value and update the constraints in real-time. It saves so much time compared to stopping and starting the simulation every time you want to change a number.
Handling the "glitchy" physics
Roblox physics can be a bit temperamental. If your car starts shaking violently, it's usually because your Stiffness is too high for the weight of the parts, or your Damping is so high it's creating a physics feedback loop.
Another thing to watch out for is the MaxForce property. If this is set to the default (which is often effectively infinite), the spring will do whatever it takes to reach its FreeLength, even if that means launching your car into orbit. Setting a reasonable MaxForce can help keep the physics engine from panicking when the car hits a wall or lands a huge jump.
Making it feel "Weighty"
To get that triple-A feel, your roblox spring constraint script suspension shouldn't just be static. You can script "anti-roll bars" by comparing the compression of the left springs versus the right springs and applying a counter-force. Or, you can adjust the stiffness based on the car's speed.
When a car goes fast, you might want the suspension to stiffen up so it doesn't flip over in corners. When it's crawling over rocks, you want it soft so the wheels can follow the ground. All of this is possible just by updating those few properties on the SpringConstraint through your main vehicle controller script.
Common mistakes to avoid
One big mistake is ignoring the Massless property of the wheels. If your wheels are really heavy, they have their own momentum that the spring has to fight against. Often, it's better to make the wheels Massless (or very light) and keep the bulk of the weight in the chassis. This makes the suspension's job much easier because it's only managing the body of the car, not the heavy spinning objects at the corners.
Also, keep an eye on your LimitsEnabled on the PrismaticConstraint. If your spring is trying to push the wheel further than the prismatic constraint allows, you'll get a constant "clunking" sound or jittering. The spring's FreeLength should ideally be within the range of the prismatic's limits.
Wrapping it up
At the end of the day, building a great roblox spring constraint script suspension is all about trial and error. You can have the perfect script, but if the weight distribution of your car is off, it's still going to drive like a shopping cart.
Start with basic values: maybe 5000 for stiffness and 500 for damping, then work your way up or down. Pay attention to how the car "settles" when it drops onto the baseplate. It should feel firm but forgiving. Once you get that sweet spot, your driving mechanics will feel a thousand times more professional, and you'll actually have fun testing your game instead of just fighting the physics engine. Keep tweaking, keep testing, and don't be afraid to let the springs get a little messy before you find the perfect tune.