did a 50 miler today and it was the first time i'd needed to use the triple on my roadbike as i went up some big-momma hills. During the ride the chain fell off three times, first when i was just starting off at some traffic lights (middle front, middle back gears). The other two were changing down to the small front granny gear. The first was not serious as i hadn't clipped in, the second two left me rolling backwards down the steep hill and i had to throw myself over (still clipped in of course) on to the verge.

I've always suspected the chain has been too slack, when stopping pedalling it will hit the frame, however the bike was new from my LBS just two months ago. I recently had re setup all the derailleurs too in accordance with the parktool website.

Anyone think i should shorten the chain, or just change the derailleur settings? It's an ultegra triple with 105 front derailleur, 9 speed on the back with ultegra rear derailleur.

Did you buy this bike new or used?

If new, have you taken it back for it's initial (usually free) tune up? ALL, new bikes need an initial break-in period. The cables when new will stretch a bit and the resulting slack needs to be removed and the shifters readjusted for smoother shifting. Same for the brakes.

Is the chain coming off at the cranks to the inside? Again, the front shifter may be out of adjustment and can be overshifting to the inside.

Also, your limit stop is probably not correctly set and is allowing for the front derailleur to be too far inward, causing the chain to come off.

Hard to tell without looking/touching the bike!

If used, did you recently replace the chain? If so, did you replace the cassette as well? What about the chainrings?

The reason I ask is, if your chain was overly-worn, you could have damaged the teeth on the cassette and chainrings as these wear out as well. If your teeth have sharp point as opposed to a flat spot near the top, they worn out and are causing some problems, but not "Chain-Drop" usually. If this is a problem, it's usually chain skip!

Once again, hard to tell.

L8R

Oops, reread your post, ignore the "used" advice.

Sorry!

Take it back and ask for your free tune up!

L8R

thanks, well the tune up will have to wait, i'm not in boston again for another two weeks so I'll try setting up the front derailleur again

Shortening the chain is an unlikely fix. However, it is worth inspection. If it is an adequate length, look again a the front derailleur. Inspect once more the derailleur height and the rotation. When you are in the smallest ring and the largest rear cog, sight the gap between chain and inner plate of the front derailleur. Is should be small. Tighten the inner limit screw to see if you can get it even smaller without it rubbing.

You state you had the chain fall off when starting from a light. Did you happen to back pedal to get better pedal position while waiting at the light? If so, it is possible may be in the rear. Back pedaling on some bikes will cause the chain to come off the rear, and when you pedal forward this misalignment may cause problems in front.

It may appear that your chain is Ok when it is actually worn out. Without proper maintenance, it could wear out within a month. To check for wear, put the chain on the largest chainwheel (front sprocket). Then looking at it from the right hand side (with the front wheel to your right), pull up on the chain at the 3 o'clock position. If the chain rises higher than half the height of a sprocket tooth, the chain is worn out and will begin to damage the sprocket.