My bikes are typically 58cm, and I'm usually comfortable on them. This summer I road a 30 year old road bike every day as an inner-city commuter, probably the most time I've ever spent on a road bike.

During the day (off the bike) I experience lower back soreness, and I am trying to figure it out. Maybe it's not the biking, but it 'feels' like it is. I typically ride for 25minutes x 3 every day, in the city, and I usually push hard even though I don't need to.

My concerns:

CRANK LENGTH?
This road bike has 165mm cranks. I am 6' foot with size 13 feet... I usually have 175mm cranks. I have been too busy to change to 175mm cranks. Would this be a problem?

DOWNTUBE SHIFTING?
My shifters are classic friction shifters mounted on the downtube. I love them, and I reach them quickly without fuss or looking down. But I've realized that I'm constantly slightly-twisting my back down to reach them, and being in city traffic I'm doing this like every 30 seconds for 25mins x 3times a day! I think the classic use of downtube shifters does not have frequent-use in mind... more like touring, long races, no stop-and-go traffic. Is this a valid concern??

HANDLEBAR DISTANCE?
Since starting with this bike in the Spring I've always wished for the hoods to be 1inch closer to me. It already has a short'ish stem. Should I be looking at 56cm for a road bike then? When coming from other style of bikes, Do people find that they need a shorter frame for road bikes, to account for how far out the hoods are? My preferred mountain bikes and flat-bar singlespeeds are usually 58cm.

I am pondering a grand solution: As much as I like road bars... put a flat bar on, with slightly longer stem, and mount a shifter on it. This removes my bending down for shifting issue, and I can probably place the flat bar at the exact spot I want with a proper stem length.