Why does this script that welds all the parts to a part only work in studio, but not ingame?

I made a script in a car, that welds all the parts in it to a part. It works perfectly in studio, but doesnt in game. Why is that?

script:

local parts = script.Parent:GetChildren()

for i = 1, #parts do
	if parts[i]:IsA("BasePart") then
		local w = Instance.new("Weld")
		w.Part0 = script.Parent.Parent.Chassis.d
		w.Part1 = parts[i]
		w.C0 = script.Parent.Parent.Chassis.d.CFrame:Inverse()
		w.C1 = parts[i].CFrame:inverse()
		w.Parent = script.Parent.Parent.Chassis.d
	end 
end

thank you