13 speeds on a single cassette sounds like marketing until you see the gear range. The SRAM Red XPLR E1 XG-1391 spans 10-44T, giving you a climbing gear that approaches mountain bike territory while keeping tight steps at the top end for road-speed efficiency. That's the whole point of XPLR—gravel bikes that don't force you to choose between pavement performance and backcountry capability.

The XG-1391 uses SRAM's XDR driver body, which matters because the 10-tooth small cog wouldn't fit on a standard freehub. XDR's smaller spline diameter makes that tight top gear possible. If your rear hub runs an XD driver (mountain) rather than XDR (road/gravel), you'll need to swap the driver body first—they're the same spline interface but different lengths.

Construction follows SRAM's X-Range philosophy with a machined steel block for the smaller cogs and individual pinned cogs for the climbing gears. The steel block handles the high-torque shifts where you're pushing watts, while the pinned construction on larger cogs saves weight where loads are lower. Full steel cassettes would be heavier; full aluminum wouldn't survive the abuse.... Read More