Joined: Feb 2005
Posts: 13,560
Likes: 44
From: Milledgeville, Georgia
Bikes: 2018 Black Mountain Cycles MCD,2017 Advocate Cycles Seldom Seen Drop Bar, 2017 Niner Jet 9 Alloy, 2015 Zukas custom road, 2003 KHS Milano Tandem, 1986 Nishiki Cadence rigid MTB, 1980ish Fuji S-12S
Yor 50/34 crankset has a bolt center diameter of 110mm. The smallest ring that will fit is 34T. To go smaller would require a different crank. Only a few double chainring cranks on the market combine road pedal spacing and lower ring capability. The 11-28 cassette will help and will probably work fine with your current rear derailleur.
If you have a Shimano 10 speed setup, you could switch to 9 speed MTB rear derailleur (10 speed RD has a different pull ratio and will not work right) and a cassette with up to 36 teeth. You'll need a longer chain as well.