SRAM XD and XDR are both cassette driver body standards used for mounting cassettes onto hubs. The main difference is the size of the driver body and the compatibility with different cassette sizes. XDR is newer and allows for smaller cogs, making it more suitable for road and gravel cycling with 12-speed cassettes. XD is older and better suited for Mountain Biking with 11-speed cassettes. Choose XDR for road and gravel cycling, and XD for mountain biking.
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