Joined: Nov 2006
Posts: 19,811
Likes: 596
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...
First of all, by my calculations, a one tooth difference between chain rings will not give you the desired half step. You'd need a difference of three or four teeth, say 39T and 42T, or 42T and 46T.
For that you would definitely need a chain tensioner.
You'd be better off with a rear derailleur and two (or three?) cogs on the hub.
But frankly I think the real problem is that headwind was just messing with your head. Is your power band really so narrow that you're comfortable at 90 RPM but not comfortable at 85RPM or 95 RPM?I don't believe it is.