I’ve got a 2015 stumpy with with the gear cable under the bottom tube! The last 2 cold rides (-2ish) my gears have froze cable I presume? Can send the mech up but won’t come back down! Ok if I’m going up a never ending hill but completely pedal spent on flats!!! Any ideas how to solve this? The bike is carbon will de-icer harm it? Any help will be appreciated

Pi55 on the rear mech, usually works.

Seriously.

Water in the gear cables, strip and clean the outers, put some wd40 through them.

As above.