3

When I'm in the highest (smallest) gear and pedaling hard, it sometimes "jumps". I'm not sure if that's the right word, but I feel a bump in my feet for a moment and then I continue pedaling. It feels like I'm shifting gears, but I'm not. I've spent some time today adjusting the rear derailleur, and all the other gears are good. Could this be caused by a worn out sprocket? I don't use this gear all that often, so I'm not sure why it would wear out faster than the others. Pedaling moderately is fine, this only happens when I push hard.

This is a 9-speed Shimano Sora.

3
  • How old is the derailleur? – sandraqu Apr 11 '18 at 13:17
  • It's from model year 2015 – Elliott B Apr 11 '18 at 14:28
  • @ElliotB By "jump", you mean the chain stays in that gear, but you feel a skip perhaps. If so, I'd agree with ChrisH below, a stiff chain link. If your chain is rusty or you keep bike outside, replace the chain. Then always use a lube on the chain like White Lightning Chain Lube. If by "jump", you mean it's shifting to a different gear, then I would consider the derailleur. If you are a daily rider, I would suggest getting a new chain and derailleur, and new shifting wires and housing. – sandraqu Apr 12 '18 at 14:53
5

It wears fast because there are fewer teeth in contact with the chain, but that might not be the cause. Here are some other possibilities:

  • A stiff chain link is most noticeable with a small sprocket. It's also more annoying if not more noticeable when under load. This tends to cause an even rhythm under steady pedalling, about one every 3 pedal strokes depending on your chain length and chain ring.
  • The high limit screw needs a tweak for some reason and the chain is trying to change gear. Even the chain tension is a possibility.
  • The derailleur has taken a slight knock and isn't quite straight.

The first two of these are best checked on a stand, turning the pedals by hand and watching the rear mech.

2
  • 3
    Worn chain and worn sprocket would be two other possibilities. As is excess road dirt wedged in between the sprockets, enough to hold the chain up higher. – Criggie Apr 11 '18 at 7:53
  • RD out of adjustment (indexing) due to stuck cable. Does the chain make some rattling noise on other gears? A dirty RD can also be a cause, grit between the high limit screw and and the parallelogram of the derailleur may falsify the setting of the high screw. – Carel Apr 11 '18 at 18:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.