I'm having a frustrating problem with a bike I otherwise love: I am unable to downshift from the big ring to the small ring in front, when I'm riding uphill.

On a long hilly ride last weekend, the problem seemed to get worse over the course of the day. If I tried to downshift on even the slightest incline, The FD would grind uselessly against the chain on the big ring.

I had to downshift before I needed to, often crossing my chain, when approaching an incline.

The FD seems adjusted correctly in other respects. The inner and outer limits are where they should be, cable tension seems correct, etc.

Any suggestions? Thanks ...