SRAM XX1 Review from Bike Magazine.
I run a 2×10 setup on the Superfish. That’s 26/39T chainring and 12-36T cassette.
Lowest gear = 26/36, which is about .72 wheel revolutions per crank revolution. Highest gear is 39/12, which is 3.25 wheel revolutions per crank revolution.
If I converted to 2×10 and wanted to have roughly the same lowest gear, I could select between the various chainrings (28-38T, by even teeth numbers), coupled with the 11 speed 10-42T cassette, to come up with a 30T chainring. That would give me 30/42, or .714 wheel revolutions per crank revolution on the low end, and 30/10, or 3 wheel revolutions per crank revolution on the high end.
In other words, with a pound or more less weight, greater chain retention security, no front derailleur or shifter, and 17-18% jumps between gears (other than the jump to the bailout 42T), I could have more than 90% of the available gear ratios that I have with 2×10. (In all reality, I’d probably go 32T, and have 32/42 (.76) and 32/10 (3.2)).
By contrast, if I went 1×10, with the current cassette technology, I could go 11-36 T. Working around the odd BCD on my SRAM X9, assume I had a 30T single chainring. That would give me a 30/36 (.83) lowest gear and a 30/11 (2.72) highest gear. The XX1 gives meaningful lower and higher gears. It’s intriguing. Darn intriguing.