Really nice ride up Hex Mtn. trail in central Washington; was in the sunny slot between thunderheads to the east and marine overcast that shrivelled up after crossing the Cascades. Very satisfying climb of ~2700 feet and fast, sometimes scary downhill (but that's what it's all about).Stupid not to take a camera.

In reply to earlier post about skipping chain: Could be as simple as your shifter indexing being out of adjustment; more seriously, a worn chain or worn chain and worn out cassette as well.