A bus interface selects bit-lanes to allocate as spares by testing the performance margins of individual bit-lanes during initialization or calibration of the bus interface. The performance margins of the individual bit-lanes are evaluated as the operating frequency of the interface is increased until a number of remaining bit-lanes that meet specified performance margins is equal to the required width of the interface. The bit-lanes that do not meet the required performance margins are allocated as spares and the interface can be operated at the highest evaluated operating frequency. When an operating bit-lane fails, one of the spare bit-lanes is allocated as a replacement bit-lane and the interface operating frequency is reduced to a frequency at which the new set of operating bit-lanes meets the performance margins. The operating frequency of the interface can be dynamically increased and decreased during operation and the performance margins evaluated to optimize performance.