SteelCan

Background:
Triple crank 9sp 105/Tiagra mix. Chain is relatively new, rear cassette has ~5000 miles.

Problem:
Chain skips when I exert power on the pedals but ONLY when I am in the big (52T) chainring. It does NOT happen when in the 42T.

This all started happening when I goofed and misaligned my front derailleur while transporting it. (tossed it in a hatchback rather than roof racks)

So I am thinking my front or rear derailleur is off rather than worn teeth on the cassette. I tried to re-adjust the front derailleur and it "seems" ok when demoing it on a stand, but when actually using it during a ride and pushing to hold a wheel or taking a pull, it skips.

Opinion?

prathmann

Are you sure the skip is happening on the cogs instead of the chainring? Usually it is on the cogs, but I experienced some skipping on my large chainring when it became too worn. At first it only happened when trying to make a fast start after stopping, but then started to also happen when pushing hard while moving. Flipped the chainring over (non-ramped) and the problem disappeared for about 40 kmiles and then returned so I've now replaced the ring.

SteelCan

It "feels" like the skip comes from the rear but not certain. Have another group ride tonight and not enough time to deal with it. Will try the large ring a few times while at the back and try to confirm.
Thanx

DOS

If its happening when chain is clearly not contacting the FD and regardless of where on rear cassette the chain is, I would guess its a worn front ring as well.

stevetone

chainring flexing when power is applied?

missing chainring bolt?

cracked crank arm?

gmouchawar

Most torque is applied with you are on the large chainring in front and smallest cog in the back (most used cog also). That is where it is most likely to skip from a worn chain or cog.
You said the chain was new? Did the skipping happen when you changed the chain as there is now a mismatch between the chain and the cog.

SteelCan

No. I only recently noticed the skipping (a short time after I transported the bike INSIDE my car rather than on the roofrack).
I think in my haste to get the bike inside the hatch, I knocked everything (derailleurs) out of alignment/tolerance. (but a worn chain and/or couple cogs could also exacerbate that misalignment)
Anyway plenty of info here. I will post up with what was required to correct the issue. Thanx
Ps: SteveT - No cracks on arm or missing bolts.

rdl456

be sure to check for a stiff link in the chain or one of the links coming off one of the rivets. I had a similar issue.

SteelCan

Ok, I "think" I found the problem. I think the hanger off the rear derailleur was bent. (I still have to now replace front derailleur cable which was splayed before I can say with certainty that this was the problem)

prathmann

No, torque applied to the rear wheel is what makes the bike accelerate. If you want to accelerate quickly from a stop (maximum torque) then you'd use your lowest gear (small front/large cog).

Using the small chainring gives you the greatest chain tension and usually the skipping will occur on the smaller cogs since these have less chain wrapped around them. Do you really use your smallest cog the most? I don't see that often, especially these days with the prevalence of 11-tooth small cogs.

To SteelCan: hope you found the problem. Let us know if it's fixed.

JiveTurkey

Bent chainring?

cny-bikeman

There are only two possibilities I can see.

One is that you have indeed bent the hanger so that the derailleur is no longer properly aligned. Because the rear derailleur cage rotates it may align differently under the small cog when on the large chainwheel vs. the small. If that is the problem you should be able to tell by looking at the alignment of the rear cog and pulleys from the rear of the bike when on a stand. Usually you would be able to eliminate the skipping by realigning the derailleur in the outer position or sometimes temporarily with just an outer limit adjustment. The skipping would not necessarily require high pedal pressure.

The other possibility is that you do have a slightly worn small cog and only the extreme pressure created when you try to accelerate in the highest gear from a relatively low speed would result in a skip.

SteelCan

I splurged for a NEW DuraAce chain and Ultegra 9sp cassette, it doesn't skip nearly as often but whenever I muscle down (for a hard acceleration or up a climb out of the saddle) I still get a skip. :-( (still a lot better than before but I obviously have some other quirks going on - I didn't have time to make derailleur adjustments before this morning's group ride but hopefully that type of adjustment will resolve this)

Oh one observation. I matched the 54links to the original chain length (which matches the calculated size of a [16.25" crank to rear axle x 2] + 52/4 + 25/4 +1], HOWEVER, there was a site I saw that had a shareware prog https://www.machinehead-software.co.u...alculator.html which if I added other criteria
(27tooth capacity, 3" distance, 11teeth) it calculates to 53links using the "rigorous" approximation. I am wondering if one less link would help.