Hi, I've set my Mtn bike so I only use the rear derailleur, which gives me a choice of 8 gears. I didn't bother fitting the front derailleur as I never need to move off the large chainring. I thought this would reduce weight too.
However, a problem I've encountered here is that the chain keeps jumping off. Initially, I thought this was just because there were too many links on the chain and so I just reduced the number. However, now the chain is shortened so it can't even reach the largest rear chainring. BUT, the chain keeps jumping off at least once on every ride! So, the problem doesn't seem to be the number of links!
So, the solution to this problem, I thought, would be to fit the front derailleur mechanism to keep the chain in place on the largest front chainring. However, to do this, it needs to be fitted with a cable and 'pulled' with the handlebar front gear lever over the front large chainring. I think the default position for the front derailleur mech is to sit over the middle front chainring.
Anyway, I hope that's clear. I'd appreciate any tips on solving this...Thx.