Originally Posted by
FreddyV
While approaching a red light I slow down and shift down to the middle chainring, 3rd cog from the left on the cassette.
Though, when the light turns green and I put some force on the pedals, the chain pops up to the 2nd cog, and the chain drops to the smallest chainring.
What can be the origin of this issue? I really hate it that this happens. It's already cost me a dropout and a set of jockey wheels and I'm not really into getting more things fixed.
Who can enlighten me?
Now this is an interesting one. To have front and rear mis-shift at the same time is very unusual, especially if the rear shifts completely to the 2nd/larger cog. Certainly rear derailleur adjustment alone would not cause that behavior. The chainwheel is fed off the rear cog, but merely shifting to inward in the rear should not normally cause the front to shift. I need to check on a few things.
1. I assume you shift to the If you shift to the middle/3rd combo just before you stop - correct?
2. Does the front or rear shift happen first, or are they simultaneous?
3. If you shift to the same combination while aready underway but at a slow speed and then accelerate does it do the same thing?
3. Any equipment changes, falls or other serious problems just before this started occurring?
4. When you check the rear derailleur do the following: Put the bike on a stand so that you can easily look from the rear derailleur toward the chainwheels. Shift to the 3rd largest cog (same as you are having problems with) but the large chainwheel in front. Check to see if the pulleys are parallel to the freewheel - not bent in or out. Then check to see if they are parallel to the center plane of the bike, that is not pointing to the left or right. Shift to the middle chainwheel and see if anything changes.
I too hope it's not a frame issue. The reaction of the frame certainly could be unpredictable enough to cause such odd behavior depending on where the problem is.