I hope someone can help me diagnose and remedy a problem that arose this morning.
My Dahon Mariner, beginning this morning, is throwing its chain to the outside of the chainring/chainwheel when shifting down, towards the bottom of the cassette (i.e. onto the small gears). It seems to be when moving from the 17t to the-- what is it, 15t?-- next smallest cog.
It happened twice, once cracking the plastic chainring guard, and both times hopping out from under the chainkeeper.
I can't clearly think what would cause this; dirty gears and chain, or maybe the freezing cold causing the chain to stick to the gears and not release as it pulls across the top? I dunno!
Any ideas on cause and course of action?