Chain comes off big ring when cross-chained

[jojoma]

Hello,

Sometimes when I'm in the 53/28 combo, the chain will pop off to the smaller 39 ring. This is a big problem because when in this 53/28 combo, I'm usually pedaling with high load on a slight rise not wanting to shift down to the 39.

Any thoughts on the main reason for this? I'm running DA 9100 mechanical which has the latest front derailleur style.

Thanks a lot for any insight.

 

[Yojimbo_]

Whenever I have derailleur problems I go to the bike shop. I've learned that if I fiddle with it myself, I make it worse.

Else, there are lots of videos and other info on the web telling you how to do the necessary adjustments.

 

[oldazcat2]

By design, bicycle chains have limited flex side to side. To see this, it helps to see this by holding a chain sideways (link pins are vertical) and see how much the chain flexes under its own weight.

Riding completely cross chained forces the chain past its normal limit. In this condition, as you’ve seen, it skips and jumps. Cross chaining regularly puts excessive wear on thebchain, chain rings and cogs/cassette.

My rule of thumb has always been, leave the extreme two cogs/gears alone. That is if you’re on the big ring, don’t shift into the two lowest (biggest) gears. If you’re on the little ring, don’t shift into the two highest(smallest) gears.

Switching chain rings quickly and efficiently takes a little practice.

 

[BrianNystrom]

That's just one of the reasons that extreme cross-chaining is not a good idea. If the front derailleur is adjusted properly, the chain shouldn't come off when you're pedaling forward, but it's likely to come off if you pedal backward. You may need to adjust the front derailleur to shift slightly farther outward or adjust the angle of the cage slightly farther outward at the rear. Also make sure it's set to the correct height above the chainring teeth. Shimano has lots of information derailleur adjustment online if you search for it.

That said, your best bet is to not use the big-big combination, which means either:

• Use the second cog in the rear and muscle it up the grade. Granted, this may not be possible.
  
• Learn to make quick double shifts (front and rear at the same time), which is a valuable skill to have.

Once you learn to do double-shifts, it's no big deal and you'll soon be doing it without thinking about it. In this case, you'll be shifting to the small ring in the front and either 2 or 3 cogs outward in the rear (2 if you're looking for a lower gear, 3 if you're looking for a comparable gear to the 53/28). Double shifts in this direction are really easy. It takes a bit more effort to go the other way, but again, once you've got the technique down, it's no big deal.