Bicycle Mechanics - What did I do wrong? Gears shifting all over the place!

This morning, there was a fall of snow. So, before setting off to work, I decided to swap my semis for a pair of big fat knobblies.

All seemed usual until I got a few miles down the road. I'd just cycled through a short stretch of snow when my gears started slipping as if the chain had difficult engaging with the rear cog.

I noticed this was only happening on 6th, so I changed to a lower gear. Soon, I had problems with all gears above 3rd -- no matter what front gear was used -- but if I put too much pressure on the pedals, even 3rd would jump about.

The jumping seemed to coincide with the turning of the pedals -- depending on what gear I was in. The cables seemed fine, so did the shifter and derailleur.

I thought the snow might be causing this, but other cyclists seemed fine and, despite the snow turning to muck and rain, the problem persisted all the way to work.

I'd like to cycle back at a better pace -- what happened?

First verify if your wheel is properly centered in the dropouts.

Sounds to me like you might have had snow jammed between your cogs. I used to have this problem on my commutes. The snow goes in, the chain packs it down, it freezes to the adjacent cogs, becomes solid ice (EXPANDING) and eventually there's enough in there that the chain can't quite reach the cogs any more. You have to pull over every 15 minutes or so and drag it out of there with an allen key or something.

[did you

Sounds to me like you might have had snow jammed between your cogs. I used to have this problem on my commutes.

Must have been in the days before I moved to Austin. ;)

Sounds to me like you might have had snow jammed between your cogs. I used to have this problem on my commutes. The snow goes in, the chain packs it down, it freezes to the adjacent cogs, becomes solid ice (EXPANDING) and eventually there's enough in there that the chain can't quite reach the cogs any more. You have to pull over every 15 minutes or so and drag it out of there with an allen key or something.
+1. When I used to winter commute I had a popsicle stick held to my bars with an elastic band. It was then instantly available to clear ice from between the cogs. It didnt happen every 15 mins, but several times over the winter months.

Must have been in the days before I moved to Austin. ;)

Damned global warming

<--you'll note I'm wearing a CU Buff's jersey in my avatar... hence the snow commutes ;)