Poor shifting in dense fog?

Question

I cleaned up my bike yesterday after a particularly wet and muddy week, wiped the oil off the chain, applied a fresh batch, took it for a spin and found no issues whatever with the shifting (I go through all the front and rear cogs to make sure the oil is distributed evenly).

This morning, however, on my way to work, shifting was a complete nightmare, it felt like either the chain was skipping or the derailleur was ghost-shifting (likely the latter). The only thing I could put it down to was the dense fog and the permeating humidity. Is that possible? Could it have somehow affected the oil on the chain?

Answer 1

I would suggest temperature change may be affecting the cable housing dimensions, which in turn affects the cable tension and therefore the dérailleur settings. I have been noticing this happening to myself this fall, especially switching to a bike with full length housing and 10 speeds on the rear dérailleur. With the large daily temperature changes in fall I find myself adjusting the rear dérailleur tension by a quarter to half-a-turn in either direction depending on how the temperature has changed. (Luckily the bike has inline adjusters near the bar, which makes this a trivial exercise).

Metal will expand or contract with temperature, and therefore the dimensions of the cable housing (which has metal strands) and the cable itself can change slightly with temperature changes.

For what its worth I never noticed this issue on older bikes with 9 speeds or lower (with or without full length housing). I have however started noticing this issue with full length housing and higher speed drive train (i.e., 10, and 11 speed).

Solution/Hypothesis Test:

If you are handy at adjusting derailleurs, then you can test this hypothesis and potential fix the problem at the same time. The next time the shifting problem emerges try adjusting the derailleur.

1. If it happens in the fog, you will likely have to add tension/elongate the housing by loosening the rear derailleur adjuster. If the shifting improves, then half the hypothesis has been verified (H1: cable housing contraction in colder weather).
2. If after (1) the weather warms up and the shifting goes off again, try tightening the rear derailleur adjuster (effectively shortening the cable housing). If this fixes the shifting then consider the second half of hypothesis verified (H2: cable housing expansion in warmer weather).

Bike Geek Aside

As an aside, the expansion and contraction of the housing and cables will counter act each other to some degree (e.g., contracting housing will lessen cable tension, but contracting cable will increase tension). Each component will also expand and contract at different rates. My anecdotal experience seems to suggest the expansion and contraction of the cable housing has the biggest effect. Another big effect I have found was adjusting the cable tension inside, where it is warm, the riding it outside where it is cold would quickly throw all my setting off.

Answer 2

Right, so I took it to the bike shop and the issue turned out to be the gear cable being loose.

The bicycle mechanic was a bit sceptical that this could have been caused by poor weather/fog so it's likely that in the process of cleaning my bike I loosened it up inadvertently (however I took it for a quick ride afterwards and it all seemed okay, so I'm not sure what happened there).

He tightened it up and adjusted the cable tension but the shifting was still a bit "sticky", so I'll have to take it again to replace the cable or possibly the derailleur and see if that fixes it.

I've noticed that someone has +1ed all comments in the question, so I take it somebody else had also found themselves in a similar predicament around the time the fog had set, though probably for a different reason.