[HELP] Changing vehicle speed

I’ve got a vehicle script with roadspikes and i want to change the vehicle speed and handling and i made this but this isn’t working out
can anyone help me or say what to change?

local _R = debug.getregistry()
local ENTITY = _R.Entity

function ENTITY:BreakTires()
	self.TiresBroken = true
	if(not self.VehicleParameters) then return false end
	local vt = self:GetVehicleParams()
		vt['steering']['speedSlow'] 	= 5
		vt['steering']['speedFast']		= 20
		vt['engine']['maxSpeed'] 		= 20
		vt['engine']['maxRevSpeed'] 	= 20

function ENTITY:FixTires()
	if(not self.TiresBroken) then return end
	self.TiresBroken = false
	local vt = self:GetVehicleParams()
		vt['steering']['speedSlow'] 	= self.VehicleParameters["steering"]["speedSlow"]
		vt['steering']['speedFast']		= self.VehicleParameters["steering"]["speedFast"]
		vt['engine']['maxSpeed'] 		= self.VehicleParameters["engine"]["maxSpeed"]
		vt['engine']['maxRevSpeed'] 	= self.VehicleParameters["engine"]["maxRevSpeed"]