Methods, systems, and devices for wireless communications are described that support different, or adjusted, random access channel (RACH) preamble formats for efficient use of shared RACH time-frequency resources. The described techniques provide for assigning different RACH preamble formats to wireless devices that have a higher link budget, whereupon the devices may transmit the different RACH preamble using the link budget available to them in one or more RACH transmission opportunities in the shared RACH time-frequency resources. Such methods, systems, and devices may allow for more RACH transmission opportunities, as well as less interference between RACH transmissions. For example, wireless devices communicating over a backhaul network may have a higher link budget than wireless devices communicating over an access network. As such, RACH preambles transmitted by the wireless devices communicating over the backhaul network may be shorter than RACH preambles transmitted by the wireless devices communicating over the access network.