I could have posted this in the mechanic forum, but I was riding my cross bike on gravel roads...
On this morning's ride I had a shifting issue, though it seems to have resolved itself. The issue was that about 1.5 hours into my ride I couldn't shift my front derailleur...with some effort it would go between the middle and large ring, but would not go into the granny ring. When I would look down at the cable (running on top of the top tube), it would look very loose like there was a lot of slack in the cable (like it wouldn't advance to where it should, so when tapping the tiagra shifter for an inwards shift it just stopped). In terms of conditions, it was about 0 celcius, and I had just finished sections of the road with some standing water and ice. My thinking is that the cable running under the bottom bracket may have iced and got stuck. I say this because when I was closer to home (dry roads in last 20 minutes of riding, and a bit warmer) it was working better, and after leaving the bike inside I was able to shift like normal. I'm using this bike in a race in a few weeks that is known to have lots of mud...
I've ridden this bike through two winters (1-3 times a week, on wet roads, roads with salt/sand...but never much snow/ice) and it's worked great. Should I replace the cables/housings? I'm guessing I should have already, but until today no sign of any issues.
Should (can) I use full housings so that the cable is better protected (not sure if cross bikes ever have full housings, like mtn bikes)?
2013 Kona Jake, 2015 Kona Jake the Snake, 2008 Kona Major Jake, 2013 Kona Jake the Snake, 2006 Kona Kula, 2012 Ridley Excalibur, 2008 Surly Long Haul Trucker, 2001 LeMond Buenos Aires, 1984 Pinarello Gran Turismo, 1982 Trek 614, 1979 Austro-Daimler
After two winters new cables wouldn't be a bad idea. Unless I've missed something about your bike full length housing isn't possible, but you might be able to run some kind of liner from the cable stop past the bottom bracket cable guide.
Since you could shift between the middle and large rings it doesn't sound like the cable was outright frozen in place. More likely something was blocking full range of motion. It could have been a chunk of ice on the cable keeping it from releasing completely to let the derailleur move to the low position. More likely (IMHO) something was blocking the derailleur itself from moving.
The better solution (not for your bike, but abstractly) that is common on mountain bikes is running the cables along the top tube rather than under the bottom bracket.