Originally Posted by tommymc

On Grant's Rivendell blog a couple weeks ago there was a teaser for a 13-42t 7 speed cassette, with normal 7 speed spacing. It could be an interesting setup on an old touring bike. But what kind of an rear derailleur would one use to reach the 42t cog? I know there are 10 speed mountain units that could handle the job. But with all the differing pull ratios on these then what 7 speed shifter would work? I suppose a friction shifter on the downtube could cover the cassette range with one of these modern RD's. One solution that comes to mind could be to use a 9 speed mountain RD that's rated to 36t and then add a Wolf Tooth or similar link. With a 9 speed Shimano RD most any 7 speed shifter should work. Any other ideas?