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I've noticed that there are times that my bike suddenly changes gears, without me touching the shifters. It usually happens when I'm on a hard gear and I suddenly power out of a full stop, it pops into an easier gear and my foot drops from the pedal. What's happening, and how do I prevent it from happening again?

  • Welcome to Bicycles @Paulo. We recommend that new members take the tour to make best use of the site, and before posting questions How to Ask is good value too. I'm pretty sure that the answer you seek is already here; maybe you can find it under the gears tag. – andy256 Aug 30 '16 at 9:36
  • How old is your bike? What is the frame made of? What kind of shifters do you have? Does the gear change back after you let the power off? Is it the left foot or the right foot powering down that causes the ghost shift-problem? – Criggie Aug 30 '16 at 10:13
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    Most likely your derailers need adjustment. In particular, as a new bike "breaks in" the cables stretch. There are cable stretch adjusters somewhere along the cables that you can twist to make up for the stretch. – Daniel R Hicks Aug 30 '16 at 11:42
  • Hi Criggie, it's a TrinX K036, and I just bought it last month. It's a 17 steel frame with shimano 7-speed rapid fire shifter combo. I've noticed that it'll change gears when I power out of full-stops, then when I ease up it pops back into the original gear. Is this normal or is something wrong? I usually start with my left foot when pedaling. – Paulo B. Aug 31 '16 at 8:05
  • As mentioned above it's probably the normal cable stretch that you get from a new bike/cable. A bit of adjustment should hopefully fix it. Many bike shops say to go in for adjustment after a few weeks anyway. Start with the simple things. No point checking to see if your chain stays are flexing just yet. – Chris Oct 30 '16 at 7:33
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If your chain is dropping on the front ring, it can be:
1. your BB is lose and shaking.
2. your derailleur not properly adjusted.
3. your crank is lose and shaking.
4. your derailleur or crank is bent.

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You need to get your derailers adjusted.

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