Originally Posted by
Hondo6
Regarding the drop bar question: flat bar shifters will in general NOT physically fit on a drop bar without modification, and modification may not be easy or even possible. Drop bar grip diameter is typically 23.8mm (15/16"), while flat bar grip area is typically 22.2mm (7/8"). You need to measure the bars you have - but I'd be surprised if their grip is 22.2mm.
A quick and dirty hack is to get a 7/8 inch wooden dowel (or just whittle some random wood 'til it fits) and jam it in the end of the handlebar then you can mount a thumb shifter as a bar end shifter.