How do i edit the BeamNG wheels?

Do i take the common.zip file unzip that and put it in the mods section somewhere?

 

What do you want to do? Add new wheels to a car?

If yes, you have to open the tires jbeam file, and change the stuff something like this (lines taken from AR162b's Grand Marshal mod):
["rim_name", ["wheel_RR","wheelhub_RR"], [], {"pos":{"x":-0.8375, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":180}, "scale":{"x":1, "y":1, "z":1}}],
["rim_name", ["wheel_RL","wheelhub_RL"], [], {"pos":{"x": 0.8375, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":0}, "scale":{"x":1, "y":1, "z":1}}],
["tire_name", ["wheel_RR","wheelhub_RR"], [], {"pos":{"x":-0.825, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":180}, "scale":{"x":1, "y":1, "z":1}}],
["tire_name", ["wheel_RL","wheelhub_RL"], [], {"pos":{"x": 0.825, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":0}, "scale":{"x":1, "y":1, "z":1}}],

Change "rim_name" and "tire_name" to whatever the rim/tire name of your wheel is.

If the rim will now be at the wrong position, not matching up with the tire like this

you can either move the tire out or rim inwards.
To do so, choose what you want to do, in the shown example the rim will be moved. It works same for the tire, just in the tires placment lines.

["rim_name", ["wheel_RR","wheelhub_RR"], [], {"pos":{"x":-0.8375, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":180}, "scale":{"x":1, "y":1, "z":1}}],
["rim_name", ["wheel_RL","wheelhub_RL"], [], {"pos":{"x": 0.8375, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":0}, "scale":{"x":1, "y":1, "z":1}}],
["tire_name", ["wheel_RR","wheelhub_RR"], [], {"pos":{"x":-0.825, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":180}, "scale":{"x":1, "y":1, "z":1}}],
["tire_name", ["wheel_RL","wheelhub_RL"], [], {"pos":{"x": 0.825, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":0}, "scale":{"x":1, "y":1, "z":1}}],

By making the number higher (positive numbers)/smaller (negative numbers) you'll move the object.
Make sure you move them by the same amount (well, no, but make the numbers look same, like if you'd ignore that "-"). For example, if you want to move the rim inwards now this would be a possible code:
["rim_name", ["wheel_RR","wheelhub_RR"], [], {"pos":{"x":-0.8325, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":180}, "scale":{"x":1, "y":1, "z":1}}],
["rim_name", ["wheel_RL","wheelhub_RL"], [], {"pos":{"x": 0.8325, "y":1.51, "z":0.32}, "rot":{"x":0, "y":0, "z":0}, "scale":{"x":1, "y":1, "z":1}}],

It'll most likely need some tries until you get a good number for this.

 

Thanks! I also wanted to know how do I change the size of the wheels? I edited the wheels.dae file and exported it to wheels.dae but the wheel size on the car stays the same

 

Thanks for the info! I forgot that the new code allows for changes within the jbeam itself without touching the DAE file.

So does this also mean that I can change the size and location of any mesh by using that new code? For example the body mesh?

Dev question: when you add something new like the scale and location code what do you have to do? Edit the core of the game? Update the game definitions? Or both