Jbeam files control everything about how a car behaves in BeamNG

Jbeam is the text-based file format that defines a car's physics, suspension, engine, wheels, and body in BeamNG. When you edit a Jbeam file, you change how that vehicle accelerates, handles corners, bounces over bumps, and falls apart. The files are plain text, so you can open them in any text editor — Notepad, VS Code, or Sublime Text all work. BeamNG reads the changes instantly when you reload the vehicle in-game, so you can test modifications without restarting the game.

Most car mods in BeamNG come with Jbeam files already written. Editing them means changing numbers and values inside those files to make the car faster, slower, stiffer, softer, or completely different. You do not need to write Jbeam from scratch to modify a car — you are usually adjusting existing values or copying sections from one file to another.

Key Takeaways

  • Jbeam files are plain text files stored in a car's folder, and you edit them with any text editor to change how the car drives.
  • The main sections you will modify are engine power, suspension stiffness, wheel grip, and weight distribution — each controlled by specific values in the file.
  • BeamNG reloads Jbeam changes instantly when you reload the vehicle, so you can test edits without closing the game.
  • Backup your original Jbeam file before editing, because a single typo or missing bracket can break the car or make it unloadable.
  • The BeamNG community forums and mod pages include example Jbeam files and documentation that show which values control which features.

Where to find and open a car's Jbeam file

Every car in BeamNG lives in its own folder. If you installed a mod car, that folder is usually in Documents\BeamNG.drive\mods\vehicles\[carname]. Inside that folder you will see several files with names like carname.jbeam, carname_engine.jbeam, or carname_suspension.jbeam. The main file is usually the one that matches the car's name.

Right-click the Jbeam file and choose "Open with" — then select Notepad, VS Code, or whatever text editor you have. The file opens as plain text. You will see sections marked with curly brackets { } and values separated by commas. Do not panic if it looks like code — you are looking for specific numbers and words to change, not writing anything new.

Before you edit anything, make a copy of the original file and rename it carname_backup.jbeam. Keep this copy in the same folder. If your edits break the car, you can delete the broken version and rename the backup back to the original name.

Understanding the main sections of a Jbeam file

A Jbeam file is organized into sections, each controlling a different part of the car. The engine section sets power output, torque, and RPM limits. The transmission section controls gear ratios and shift speed. The suspension section defines spring stiffness, damping, and ride height. The wheels section sets tire grip, size, and rolling resistance. The nodes section defines the car's weight and structure.

You do not have to understand every section. Most common edits target just one or two: making the engine more powerful, stiffening the suspension, or increasing tire grip. Each section starts with a name in quotes, like "engine" or "suspension", followed by an opening bracket. Everything inside that bracket until the closing bracket belongs to that section.

Look for the value you want to change — for example, "maxPower" for engine power, measured in watts. A typical car might have "maxPower": 150000. If you change it to "maxPower": 300000, the car will have twice the power. The number after the colon is what you edit.

Common edits: power, suspension, and grip

To increase engine power, find "maxPower" in the engine section and raise the number. Doubling it makes the car twice as fast in a straight line. To make the engine rev higher, find "maxRPM" and increase it — this also increases top speed if the gearing allows it. To change how quickly the engine responds, look for "torqueCurve" and adjust the values there, though this is more complex.

To stiffen the suspension, find the suspension section and look for "spring" values. These are measured in newtons per meter (N/m). A higher number means a stiffer spring. Typical values range from 20,000 to 80,000 — raising them makes the car sit lower and handle sharper turns without rolling as much. To soften it, lower the numbers. Also look for "damping" values, which control how quickly the suspension bounces back. Higher damping stops bouncing faster but makes the ride harsher.

To increase tire grip, find the wheels section and look for "grip" or "friction" values. These are usually decimal numbers between 0.8 and 1.5. Raising them makes the tires stick better, especially in corners. Lowering them makes the car slide more easily. You can also find "brakeFriction" to change how hard the brakes grip.

Testing your edits in BeamNG

Save your Jbeam file after making changes. In BeamNG, go to the garage and select the car you edited. Click "Reload" or close and reopen the vehicle selector — BeamNG will read your new Jbeam file. Drive the car and feel the difference. If the car does not load at all, you likely have a syntax error: a missing bracket, a missing comma, or a typo in a section name.

If the car breaks, check the BeamNG console for error messages. Press Ctrl+Home in-game to open the console and scroll up to see what went wrong. Common errors include missing commas between values, unclosed brackets, or a value that is not a number when it should be. Close the game, fix the error in your text editor, save, and reload.

Make small changes and test often. Change one value, reload, and drive. This way you know which change caused a problem if something goes wrong. Large changes to power or suspension can make the car undrivable or crash the game, so start with 10 to 20 percent increases or decreases.

Copying and combining parts from other cars

You can copy entire sections from one Jbeam file and paste them into another. For example, if you like the engine from one car and the suspension from another, you can take the "engine" section from the first file and the "suspension" section from the second, then paste both into a third car's Jbeam file. This is how many custom builds are made.

When you copy a section, make sure you copy the entire thing — from the opening bracket after the section name all the way to the closing bracket. Paste it into the target file in the correct place, usually after another complete section. Make sure there is a comma after the closing bracket of the section you pasted, unless it is the last section in the file.

Test the combined car carefully. Mixing parts from different cars can create unexpected behavior — a powerful engine in a light car might make it spin out, or a stiff suspension on a heavy car might make it bounce wildly. Adjust the values to balance the car after combining sections.

Avoiding common mistakes

The most common mistake is forgetting a comma or bracket. Every value should end with a comma, except the last value in a section. Every opening bracket { needs a closing bracket }. If you add a new line or value, make sure the comma is there. A missing comma breaks the entire file.

Do not change section names or the structure of the file — only change the numbers and values inside sections. If you rename "engine" to "Engine" or remove a bracket, BeamNG will not recognize that section. Stick to changing numbers like power, stiffness, and grip.

Do not make extreme changes all at once. A car with 10 times its original power or suspension stiffness will likely be undrivable or crash. Start with 20 to 50 percent changes, test, and adjust from there. This also helps you understand what each value does.

Frequently Asked Questions

What text editor should I use to edit Jbeam files?

Any text editor works — Notepad comes with Windows, but VS Code and Sublime Text are better because they highlight syntax and make it easier to spot missing brackets or commas. Do not use Word or Google Docs, because they add formatting that breaks Jbeam files.

Can I edit a car's Jbeam file while BeamNG is running?

You can edit the file, but BeamNG will not see the changes until you reload the vehicle in-game. Close the car from the garage and reopen it, or press the reload button if your version has one. The game reads the file fresh each time you load the car.

What happens if I make a typo in the Jbeam file?

The car will either not load at all, or it will load with default values for the broken section. Check the BeamNG console (Ctrl+Home) for error messages that point to the line number with the problem. Fix the typo, save, and reload.

Can I undo my edits if I mess up the car?

Yes — that is why you made a backup copy before editing. Delete the broken Jbeam file, rename your backup back to the original name, and the car will work again. If you did not make a backup, you can reinstall the mod or find the original file online.

How do I know what values are reasonable for power or suspension?

Look at other cars in BeamNG and check their Jbeam files. Open a few stock cars and a few mod cars to see what their power, spring stiffness, and grip values are. This gives you a sense of the range. Community forums and mod pages often include notes about what values were changed.