SRAM created the XDR drivers and XD drivers to allow us to run cassettes that had cogs with less than 11 teeth, which is great if you want to go and run a 1x drive train and still have a big top gear. It will help to eliminate the topping out that some of us were getting on the flat and the much more likely topping out when we were descending.
If you’d rather see a video about XD and XDR driver body explain, watch the SRAM video below
The story about XD driver body
In 2015 SRAM brought us the XD driver in order to let us have a 10 tooth cassette cog. The use of the 10 tooth cog allows cassettes to have a wider gear ratio and it allowed SRAM to prove that 1 x 11 setups could work as well as double chainring setups. You can now find 9 tooth cogs from some of the smaller more niche cycling component suppliers.
SRAM released XD with an open patent, so many companies jumped onto the bandwagon and started to produce their own XD drivers. This was helped by the fact that XD was designed to work with current axle designs and ratchet mechanisms. The only major player who has not got involved is Shimano.
SRAM also states that the XD driver has benefits over a traditional freehub. Your cassette will be less likely to wobble and cut into the freehub body, on an XD driver. As the freehub is then more stable, you can then expect the bearings to last a longer time.
What is the SRAM XDR？
XDR is the road version of the above XD driver. It is designed to work on road-specific 11-speed wheels, that is why it is 1.85 mm longer than the XD driver. It has the same advantages as an XD driver has over traditional freehub bodies and you should also save between 6 and 8 grams over a standard freehub body.
The best thing about both XD and XDR drivers was that they had saved us all from having to re-dish our wheels when we jumped up to a larger cassette. Spending less time in the workshop means we can all spend more time out enjoying our bikes.
Do I need an SRAM XD driver or a XDR driver?
If you like getting dirty on a carbon mountain bike, then you’ll be looking for an XD driver. An XD driver takes up the same room as an 8,9,10 speed HyperGlide freehub body.
However XDR drivers are for use on road, gravel bike, and cyclocross bikes. It comes in at just under 2mm longer than an XD driver and is designed to fit in the same place as an 11-speed HyperGlide freehub body. The simple way to remember the difference is the R tells you it is for road-based bikes.
The XDR driver can run 10 speed XD cassettes provided you shim the cassette with a 1.85 mm spacer.