55x19 is fine to start with on a 23c tire. I ran about the same for awhile untill I started getting hit with wind. That nice 22-23mph cruising speed gets nailed in headwind so I geared down just a tad to 73GI and it helped and I can climb decent grade with the 73GI. On my last long ride I walked two hills that had everyone else in their granny gear rolling as fast as I was walking, so it's all relative I guess.