I am back from the bike shop with the 18T cog installed. The technician made a few other minor adjustments to the seat and handlebars while I was there. It seemed much better during my short parking lot test drive. I will take it on a ride later on and will report back here after that. It's too blasted hot out there right now (feels like 93 with the heat index, and that's a little cooler than it has been recently).