Joined: Nov 2006
Posts: 19,810
Likes: 597
From: NJ, NYC, LI
Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
What's the bike?
I don't know if it came like that, but assuming you have a two-speed derailleur and two cogs on the hub, spaced 2T apart (like a 21 and a 23) it should be a good system. Eight evenly spaced gears, and slightly wider range than the 4-sp alone.
I had that same setup on my Fothergill for a while but the hub had problems, so switched to a 3-sp hub for 6 gears.