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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?

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    Unlikely - water and oil don't mix. Did you lube it with something else by mistake? (I've used spray-on electrical contact cleaner instead of galvanising spray paint before, very similar cans and lack of attention) More likely that your cleaning regime has put something out of alignment, or is the chain actually worn? – Criggie Nov 2 '15 at 9:13
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    No, same oil I've always used, very similar to this. Chain should not be worn - I replaced the chain and the rear freewheel less than a month ago and I checked it for wear last week using a chain wear tool. Yesterday everything checked out, I'm going to wait for the fog to dissipate and take it for a quick spin, see if the built-up moisture on the cogs wasn't to blame (fog was unusually thick this morning, droplets of water had built up on all sorts of surfaces). – Nobilis Nov 2 '15 at 9:39
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    Apart from just wiping the oil off the chain, it may be worth giving the chain a proper clean. Use a chain cleaner (such as the ones from Park Tool or Muc-Off) device and specific chain cleaner liquid. If you can, remove the chain completely and let it soak for a while. Afterwards, ensure it is rinsed and dried completely before lubing it. I use these: wiggle.co.uk/park-tool-cm52-cyclone-chain-cleaner and wiggle.co.uk/… – RoKa Nov 2 '15 at 11:56
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    Is it much colder than last week where you are? I'm guessing given the fog that you're in the UK and no. Could it be that the chain sat wet for a while after cleaning and rusted, or was too wet for the oil to get in? – Chris H Nov 2 '15 at 12:03
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    @RoKa Thanks, I have that tool and use paraffin to with it, but might be worth taking it it off and letting it soak (I do believe it has one of those links that let you detach it). – Nobilis Nov 2 '15 at 12:16
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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.

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    Thanks for the detailed reply! I'm not very confident at tweaking with the gears, so will take the bicycle to the local bike shop for an inspection and will update the question on the outcome, but what you suggest seems to be the most likely cause (as it was fairly warm yesterday, then the fog settled, it got very cold, could see my breath and it's still lingering). – Nobilis Nov 2 '15 at 19:52
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    @Nobilis - you may consider asking them to show you how to adjust the rear dérailleur. It's an pretty useful skill for a daily rider and most shops are quite friendly (especially if you consistently buy things there!) – Rider_X Nov 2 '15 at 20:01
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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.

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    Unless the derailleur has gotten sloppy (i.e., highly worn pivots) you shouldn't need to replace it. I would personally do this as the last step (especially considering the cost). In terms of settings changing with temperature, I live in climate very similar to London. And right now, consistently on a daily basis, a quick 1/4 turn on the derailleur morning/evening gets the shifting working bang-on, otherwise it is always missing shifts. For me least temperature is having a noticeable effect. Bike shops aren't always well-known for following the scientific method. – Rider_X Nov 3 '15 at 19:41
  • @Rider_X I'll have the cable replaced at least as I've owned the bike second hand for a year and a half and have never inspected it, yet I do ride a lot and shift up and down frequently as I'm particular about my cadence due to my knees. I do appreciate your advice and will keep it in mind, I'm thinking about investing in a maintenance stand so I can make these kinds of problems easier to address. – Nobilis Nov 3 '15 at 20:46
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    Hopefully, the new cables will fix the problem! A bike stand definitely makes maintenance (such as wiping oil off the chain) much easier. – Rider_X Nov 3 '15 at 21:59

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