On 2018-10-04 12:12, Duane wrote:
On 04/10/2018 1:29 PM, Mark J. wrote:
On 10/3/2018 9:04 AM, jbeattie wrote:
On Tuesday, October 2, 2018 at 8:14:46 PM UTC-7, Frank Krygowski wrote:
On 10/2/2018 2:10 PM, jbeattie wrote:
O.K., reality check. I was riding in with my son this morning, and
he had a sudden attack of ghost shifting or skipping of some sort.
I was watching his rear wheel (my usual position, hunkered down
behind him), and I didn't see chain skip.

IME, ghost shifting usually happens with a sticky cable at the BB,
but what is the likelihood that this is a casette/chain issue? I
changed the chain but not the cassette a month ago. It worked
beautifully -- no skipping, but I'm wondering if you can hit a
tipping point where the cassette goes and the chain is O.K., and
you get shift issues. If the cassette is too worn, I usually get
problems the moment I put on a new chain and not later.

I guess I don't understand. To me, "ghost shifting" always meant the
bike tries to at least partially shift to a different rear cog. My
folding bike does that sometimes until the cables settle in after being
folded for a while. If I look down, I can usually see the unbidden
attempt at a shift.

Did you see his chain move laterally? If not, I wouldn't call it ghost
shifting.

When I've put a new chain on a too-old cog and gotten chain skip, it's
always occurred only under heavy pedal pressure; and while it's
probably
visible from the rear, I've never been able to actually see it happen.

I was watching it this morning, and it isn't ghost shifting. It is
skipping in 11/12. The chain is not moving laterally -- its just
jumping on the cog. He's going to check derailleur tension at work
(they have a shop there). The cassette is tight, and the only other
explanation, IMO, would be worn cogs.

This is the Roubaix that was stolen and found by Bike Index and PPB.
https://bikeindex.org/news/bike-inde...018-recoveries (the
post with the mug shot -- the thief actually has a nice haricut). It
had fairly low mileage and an OE cassette. I put a new 11sp chain on
it when I rebuilt it because someone had side loaded the existing
chain and popped a link or somehow popped a link. They also banged up
the chain ring. When I installed the new chain, it shifted
beautifully and still shifts beautifully on the stand. I checked it
this morning. It may be the case that the cassette had more mileage
on it than I recalled.

-- Jay Beattie.

Don't rule out munged cogs, perhaps bent by whatever damaged the chain
while the bad guy had the bike. Who knows what bizarre treatment the
bike was subjected to?

Mark J.



In my experience what often happens is that you let the chain go too
long and when you change the chain the cassettes are worn enough to
cause slip on the new chain.


That is also what I think. Once I let the chain on my MTB accidentally
go to 1% stretch instead of the usual 0.8%. Put on a new chain. It
worked fine for 100mi or so and then started skipping on the smaller
cogs - cassette was shot. New cassette, problem solved. 55 bucks, ouch.

--
Regards, Joerg

http://www.analogconsultants.com/