New Bike Cable Stretch Question

[Bike Writer]

Why would this happen just after two months? Do limit screws come loose?

If I look at your earlier post this happened on day 2 originally so I don't think it's "coming loose" it sounds like it was not set right from the get go...good idea to have a pro check it out, especially one you trust...he/she will give you guidance about that.

[Mama Coosa]

It's not unheard of for limit screws to suddenly be out of adjustment for no obvious reason, but it's also not very common. If your bike is that new and the chain is coming off, then it most likely wasn't adjusted correctly from the start, as others have already said.

Front derailleur adjustments are like black magic for many bike mechanics. There's a lot goin on up there. To get a better understanding of how your limit screws work, shift your bike so that the chain is on the small chain ring. Examine the limit screws and locate the ends of the screws where they interface with the inner part of the front derailleur. While watching this area, pull the derailleur cage (the curved silver part) toward you. Watch how the distance between the derailleur and the end of the screw varies with the position of the derailleur cage. Notice how, when you pull the cage toward you, you see the gap on one of the screws gets smaller until the inner derailleur actually touches the screw. This is how you can identify your high limit screw; the one that keeps the chain from falling off the rings to the outside. That screw that is touching the derailleur is limiting how far out it can move. Look at the screw and the derailleur and imagine what would happen if you tightened (righty-tighty) the screw that is touching. The screw would go further into the derailleur and would further limit the outward mobility of the derailleur cage, thus, keeping your chain on the big ring.

Now, mind you, a properly tuned front derailleur requires a delicate balance. Much like life. If that screw we were talking about is tightened too much, then it will prohibit the derailleur from moving out far enough to push/allow the chain to move onto the big ring.

Of course, none of this really matters if your other front derailleur adjustments aren't correct. If your derailleur is clamped too high above the crank (an often overlooked adjustment), it's going to throw off your limit screw adjustments. If your derailleur got bumped and the cage isn't parallel with the rings, it's going to throw things off. There are numerous other issues that can cause problems with front shifting, but I'm tired of typing, so we're not going into that right now.

This is why front derailleurs cause so much grief. It's like trying to fine tune a see-saw designed for six people. The trick is making all parties cooperate.

To the OP: Like I said, front derailleurs are tricky and bike mechanics aren't perfect. My advice would be to go back to the shop and tell them exactly what the deal is. Make sure you ride the bike when you pick it up, before you put it in or on your car.

If the problem occurs again, either get a new mechanic or teach yourself.

Most importantly, congrats on the new whip!