The present teachings relates to methods performed in a network node of a wireless communication network. The method comprises: broadcasting one or more threshold values enabling the wireless devices to determine fulfillment of one or more criteria for selecting a contention based random access preamble either from a first preamble group or from a second preamble group for use in a contention based random access procedure; transmitting to a selected wireless device one or more threshold values using dedicated signaling, the one or more threshold values sent in the dedicated signaling overriding a corresponding broadcasted threshold value and being set so that the wireless device fulfills the criteria to select a preamble from the first preamble group, wherein the threshold values sent on the dedicated signaling differ from the broadcast threshold values; and prioritizing preambles of the first preamble group over preambles of the second preamble group.