Say you were running a 32t chainring on the front, and this 42 on the back, would it not be the same as having it the opposite way round (42 front an 32 rear)? If so, I don't get it. I'm sticking with a triple for now.
No, it's not the same...
I could work it out in gear inches for you but I've always found ratios easier:
42f/32r = 1:1.3125
32f/42r = 1:0.762
The wide range on the 10-42 cassette wouold give you an "extra" gear at the top and bottom of current setups (the 10-tooth being a higher gear than current 11's and the 42 being much lower than current 36's)
So if I (as an example) wanted to run this I could fit a 38-tooth single to the front and still retain the same "hard" gear as with my current 42-tooth big ring but i'd lose my lowest gears (that I rarely use anyway).
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Just a y2k FSR with some modern bits