Devices and methods are provided for adapting the allocating of random access resources to user equipments of a cell served by a base station. A method in a base station where each RA preamble group maps or corresponds to an uplink allocation size comprises receiving a RA preamble from a UE in a cell served by the base station, the preamble indicating a requested resource allocation size for uplink transmission of UE data. Radio resource usage in the cell is monitored and a mapping between groups of RA preambles and uplink allocation sizes configured for the cell is adapted based on the monitored usage of radio resources. UEs or MTC devices are thus provided with an efficient means to have their UL allocation needs met for transmission of user data in conjunction with the Random Access procedure.