so when i'm on my middle front ring and smaller ring on my cassette... my chain drags on my front derailleur and my gears feel like they skip. there's nothing wrong with the teeth on any cogs and the chain isn't catching on the derailleur... it's just draggin. can a chain lose it's tension over time and if so is there some way to tighten it. i think i just have to adjust cable tension for the derailleur but what can i do about the "skipping" gears???