Antti Salonen said:It was a warm and sunny day, and I was riding my new single-
speed Surly road bike. About 60 kilometres into the ride
the chain basically just dropped inside the chainring.
This happened on a flat section of the road, when I was
spinning at a high cadence, so nothing dramatic
happened. When I stopped, I noticed that the chain was
off the freewheel too, so I don't know where it derailed
first. So, I loosened the nuts, put the chain back on
and rode home.
The bike has a rampless Blackspire DH chainring and a
Shimano BMX freewheel, the chain is an SRAM 1/8" chain.
The chainline is perfect. The chainring is properly
centered. I have ridden the bike for about 290 kilometres
now and this has never happened before (or after). There
are two photograph of the setup at:
pp.fishpool.ficrosscheck.htmlOpen ↗
pp.fishpool.ficrosscheck2.htmlOpen ↗
What are the likely reasons for the chain to derail like
that? I had removed the chain for maintenance before the
ride, and while it's possible that the chain wasn't as
tight as it could've been, there was no (visually)
noticeable droop. The nuts were tight. My usual routes
have some steep hills, and I certainly wouldn't like the
chain derailing on one of those.
Both the chainring and the freewheel would also work with
a
3/32" chain. Would this be a good idea?
I've got a hybrid with a SRAM Spectro S7 internal-gear hub.
This has a single chainring and single rear sprocket.
I too have suffered a few thrown chains, until I worked
things out.
Most importantly, your chain is not tight enough. See
parktool.comchaintension.shtmlOpen ↗ for
specific advice on this.
In my experience, you will keep your chain at the correct
tension for much longer if you pay special attention to
chain lubrication and cleanliness. I have 2 chains in
circulation at any one time. One is on the bike, and the
other is prepared for its next use.
I wash the dirty chain thoroughly in mineral solvent. The
first few rinses are done with used, decanted solvent. The
final rinse or 2 is done with fresh solvent.
Then I let the chain dry thoroughly in the sun for a day.
Then I "soak" in Mobil 1 engine oil for a day. Finally, I
drain it, and wrap it in a clean rag until it's ready to be
used again. Plenty of oil remains within the rollers to
ensure lubrication for 1,000 to 2,000 km in good conditions.
With this regime, I usually don't need to readjust the chain
between cleanings.
I've found that the loose chain derails at high speeds on
uneven surfaces. Under these conditions, the chain can build
up a strong side-to-side oscillation which will derail it if
there's enough slack.
Finally, you might consider using a chain which is designed
*not* to derail (instead of the usual chains which are
designed to promote derailment). I'm thinking specifically
of the KMC K710
(1/8"😉 or K810 (3/32"😉. See
home.earthlink.netenglishOpen ↗ under "BMX
/ Freestyle". Note that these are not lightweight
chains, however.
In size, I switched from 1/8" to 3/32", and haven't
looked back.
John
