I bought a bike equipped with Shimano A550 Dual Pivot Caliper brakes, drop bars, and Shimano Tiagra ST4500 combo brake levers and shifters. I wish to change the bar to a flat type, and the combo levers will not work for this. What makes and model break levers can I use that will give me good modulation and feel? Obviously I will use separate shifters. TIA for any insight you might have.