Bicycle Mechanics - Chain drop on compact set-up
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I have a SRAM Force compact 50-34 and 11-28 setup and am experiencing occasional chain drop when shifting to the 34 ring. I try to stay in the middle of the cassette before shifting down, and also let up a bit on the pedaling pressure. And of course, it never happens on the work stand or riding on flat terrain. Was thinking of putting on a chainwatcher; however, the local LBS says when everything is properly adjusted, chain drop shouldn't happen.
Any thoughts as to type of chainwatcher or other suggestions are appreciated.
02-17-12, 09:47 AM
Cahinwatchers are always a good idea. Even if you have everything adjusted properly they are good insurance. There are several available types. The Third Eye chain watcher is readily available in bike shops and the N-Gear Jump Stop ( http://n-gear.com/) works well and is the one i have on most of my bikes. The only "problem" with these is they need a round or nearly round seat tube to mount on. The "K-edge" chain catcher ( http://www.acecosportgroup.com/shop/k-edge-chain-catchers.html ) comes in several models including ones that fit braze-on front derailleur tabs for non-round seat tubes.
02-17-12, 10:03 AM
Did you make sure your low gear limit stop is properly adjusted? See: http://sheldonbrown.com/derailer-adjustment.html
Sheldon Brown: "The basic adjustment for the low-gear stop is to set it so that the chain just barely clears the inner plate of the cage when the lowest gear (small front, large rear) is selected. This will usually be the best position for double-chainwheel setups, and will permit the use of most or all of the rear sprockets with a minimum of trimming."
02-17-12, 10:17 AM
^^ Yes, proper adjustment will prevent MOST chaindrops MOST of the time. A chainwatcher is for that occasional time that is the exception due to a shift under bad conditions or whatever.
02-17-12, 11:44 AM
You might also want to pay attention to your shift speed/force. Start by downshifting slowly and methodically- you should NEVER get drop then, but if you do it's definitely an adjustment issue. Then gradually speed it up until you have a drop & you'll know how hard/fast to push things.
When I rode with my daughter last year (both of us on my bikes) she would drop at least once a ride. After using the above suggestions, it stopped completely.
02-17-12, 02:08 PM
I put a chain-watcher on my triples.. on some added a chainguard disc, outside.
then there are only 3 places for the chain to land, the chainrings..
Even added one to my Bike Friday PL, as there is a chain tensioner with the Rohloff hub,
so some bounce-off is possible ..
and a disc guard supplied on the outside..
Ka thunk throws of index FD schemes may have more tendency
than hand operated friction levers.. operator care..
02-17-12, 02:50 PM
A friend had this problem. Turned out the bike shop had installed the small ring backwards!
02-17-12, 04:09 PM
+1 on the N-Gear Jump Stop; I install them on all of my bikes. I agree with Hillrider, it's easy insurance against that 1 time in 1000 when the chain drops; I hate getting greasy fingers when I am on a ride.
02-17-12, 04:17 PM
The jump from 50 to 34 is obviously doable, but it stretches the limit of what is reliable. Assuming the small ring is indeed mounted properly, the derailleur is mounted at the proper height and rotation, and the inner adjustment is right, you need to install a chain watcher.
Your LBS is wrong. SRAM DRs have strong springs and if the top run of chain is at all slack, it can get thrown off the inside of the small ring when downshifting. Keeping a small amount of tension on the chain while downshifting will help prevent this. Better yet is to install a chain catcher. The new SRAM Red FDs come with an integral chain catcher for this reason. K-Edge catchers work well and look good, but there are other similar that also work well.
02-17-12, 05:31 PM
You might also want to pay attention to your shift speed/force.
+1 usually drops like this are more user error than anything else. Most riders down shift because they are going to climb a hill. Make sure you give the drive train time to engage before you start pushing up the hill. If there is too much pressure on the pedals when you downshift, there is the probability that as the chain releases from the big chainring, you may spin the crank a link or two before the chain engages the small chainring, which can cause a dropped chain. When you downshift, take a little pressure off the pedals until you feel the chain has fully engaged the chainring and then travel on..
02-17-12, 10:04 PM
+1 for a chain watcher. Just about every pro in the peloton rides with one. It's cheap insurance.
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