[DarkRP 2.7] TDM cars can be set to No collide through Context menu.

How would I go about disabling collision off for vehicles?

properties.Add( "collision_off", {
	MenuLabel = "#collision_off",
	Order = 1500,
	MenuIcon = "icon16/collision_off.png",
	Filter = function( self, ent, ply ) 

		if ( !IsValid( ent ) ) then return false end
		if ( ent:IsPlayer() ) then return false end
		if ( !gamemode.Call( "CanProperty", ply, "collision", ent ) ) then return false end
		if ( ent:GetCollisionGroup() == COLLISION_GROUP_WORLD ) then return false end

		return true 


[editline]17th August 2016[/editline]

Would this work?
if (ent:IsVehicle()) then return false end

Use this hook instead of editing base files:

It doesn’t tell me which file to put this in.
Where would I add this Hook in DarkRP?

Create a new file with shared realm (Not autorun/client or autorun/server)
And put the hook there