Weight Weenies

My wife's 43cm Litespeed has a shifting problem. Set-up is Ultegra 10sp with FSA Gossamer compact 50 - 36 ring combo, 12 - 25 cassette.

When in her smallest gear (36 x 25) when she comes out of the saddle the chain will try to jump to the next cog down (the 23) . If I tune the rear derailure so that this does not happen, then when in the 23 the chain will try to jump to the 25. It is as if one notch on the rear derailure adjuster is too much one way or the other. Even with the barrel ajuster on the downtube there seems to be no way to get the chain to hold properly on both the 25 and 23 for hard efforts. It's one or the other. Sometimes it will completely ghost shift but then jump back. Most of the time the chain just dances around trying to decide what cog it wants to be on.

The only things I can think of are:

1. RD alignment

2. Cassette wobble. Ever notice on some hubs when you spin the wheel the cassette does a little wobble? Her wheels are Shimano 540's and the straightness of the axel/hub/freebody is not so great. The cassette has a slight wobble while freewheeling or pedalling. Are the tolerances of the 10 speed drive train so small that this wobble could be causing the chain to grab cogs other then correct one as the cassette moves laterally a bit throughout its rotation?

ANy suggestions would be welcome. Thanks in advance.

does it do the same in the big ring?

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Try the bolt to adjust the rd a bit more to the spokes, maybe this helps.
The high gear adjustment screw on the pic.
Maybe the derailleur can't ge enough to the left after this tune it with the cable tension screw

The limiting screw is not the problem. It is set so that it is possible to adjust the RD so that it easily gets the 25 cog.

have you checked to see that the hanger is not bent?

also check the wheel dish, and the wheel is out of dish, the bike will have poor shifting. if the cassette has a wobble than it is likely that the hub isn't straight, if you don't have a tool, you can get an idea of dish by putting the bike into low gear (39, 25) and high gear (53, 12) and sighting it along the chain line to see that the chain is straight if it isn't straight than the hub might not be dished.

Cassette wobble. Ever notice on some hubs when you spin the wheel the cassette does a little wobble? Her wheels are Shimano 540's and the straightness of the axel/hub/freebody is not so great. The cassette has a slight wobble while freewheeling or pedalling. Are the tolerances of the 10 speed drive train so small that this wobble could be causing the chain to grab cogs other then correct one as the cassette moves laterally a bit throughout its rotation?

Sounds like this is the problem, if in fact the RD is properly set and adjusting doesn't do the trick...

lance also brings up a good point, but just the fact that you know of an existing problem with the hub/ axle tells me this is the cause...

try resetting the RD, and if this doesn't solve the problem... try another wheel...

good luck... and post your findings...

beat you.

lol, damn sympatico

Hi Mr. Gib,

Your trouble is probably caused by frame flex, changing cable tension under load.
First, check for proper chain length: leave it just long enough to allow for the 50-25 gear (which you will never use, I know...), so the top pulley doesn't get too close to the freewheel cog. This is important, as a small distance from cog to pulley makes the shifting more 'nervous'.
Increasing the distance by moving the adjustment screw at the back of the derailleur (the one that holds against the dropout notch) may help.

Another way of dealing with frame flex is changing cable routing. Try running the shifting cable from the rear lever to the left hand adjuster on the frame, from the front lever to the right, then change sides under the down tube (I don't know if this is possible with your frame).
If this doesn't solve your problem, you could opt for a one-piece cable housing from lever to derailleur, eliminating the frame's influence completely. But this is weight weenies...
Alright then, have fun!

Frame flex was my first thought as well. The wheel isn't going to be an issue. The little bit of wobble the cassette has is suposed to be there. It is not that the 10sp has such a low tollerance that the wobble causes a mis-shift, the wobble actually adds more tollerance to avoid mis-shifts.

Your possible problems:

- Frame Flex distorting cable tension (on that size frame i'm thinking she might not be big enough to flex the frame to the point to cause a mis shift)
- Improper cable tension
-Lower limit adjustment
- Chain length
- Rear der hanger might need to be alligned

Most importantly and I can't believe it hasn't been mentioned yet, how many miles are on the cassette and chain? And were they both installed together as new?

Seing as how they wear together, it might just be time for a new chain and cassette. Especially if she uses the 23 and 25 frequently. Check the chain for stretch and the cassette teeth for wear and roundness.

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