Mike This is a very common issue with several very simple fixes. I apologize in advance for a long post
As you know, there's a spring in the front derailer that wants to pull the chain down to the small ring. The only thing stopping that from happening is the friction in the shiftlever. If there's more static friction in the shiftlever, it'll keep the front derailer in place. If the force in the derailer spring is stronger, it'll win and pull the chain over. When you pedal out of the saddle, the frame flexes some and makes the cable a little tighter a little looser in phase with your pedalling. If the friction in the lever is just barely strong enough to hold the derailer in place, this part can make the derailer walk down to where it's constantly rubbing and requires you to pull the shifter again to take up the slack. This problem is more common these days because modern front derailers have ridiculously strong return springs because of all the mashers who insist on being able to downshift to a smaller chainring while hammering out of the saddle. Furthermore, the lever arm on the ft derailer linkage is much shorter today than in older derailers, making the front derailer 'stronger' because of an increased mechanical advantage. This 'enhancement' developed to get brifters to work. So the fixes can include: 1. If you have a 'modern' front derailer, consider swapping it with an older design. One with a lighter spring and/or longer lever arm 2. Get more friction out of your friction shifter. If you tighten up the d-ring all the way, you should no longer even be able to move your shifter in the downshift direction. If you can't do that, then you aren't really tightening the friction part of your shifter. You've merely bottomed out on the bolt and you are tightening against that. You need a shorter bolt, or a slightly thicker friction washer inside. 3. Another modern front derailer 'enhancement' is a SUPER narrow cage. One of the consequences of that is you have to have your limit screws set really precisely, and you have to slam the derailer against the limit screw when you are in the big ring and a smallish cog. In this situation, the tug-of-war is no longer the front derailer spring against the shifter friction. It's an immovable object (the limit screw) against the friction in your shifter. The limit screw always wins, and you'll always be able to get a tiny bit of slack in the cable. To check if this is what you are experiencing, deliberately back off the upper limit screw a lot. Like a full 360 degree rotation. You'll have to be careful not to overshift when you go into the big ring. When in the big ring, see if you can make the rubbing happen. You might not be able to. If you find that backing off the limit screw 'solves' the problem, then you'll be left trying to find a balance where there's a combination of limit screw setting + technique that keeps you from overshifting and avoids this phenomenon. Another surprising fix for this particular corner case is flexier shift cables. People forget how springy shift cables used to be. These days, they are super stiff in tension to make indexing work. A springier cable can take the stress cycles associated with pedaling without moving the shifter. It's hard to find springy shift cables, these days, though. On Monday, July 2, 2012 10:48:44 AM UTC-7, Mike wrote: > > On Jul 2, 9:08 am, Scott Henry <ske...@gmail.com> wrote: > > Just curious, is the front shifter slipping or is the front derailuer > just > > rubbing? > > If it only happens during hard efforts, it may be due to frame flex > rather > > than shifter slip. I'm assuming you are in the big ring and try to > hammer > > when the frame flexes away and effectively tries to stretch the length > of > > the cable, due to the FD outer limit screw the FD can't move and thus > pulls > > the cable with moves the lever... > > I haven't ruled out frame flex being the culprit. I feel like I've > talked with a number of people of varying sizes who have had this > issue on various bikes. I've had it a bit with my LHT on sustained > stand-up efforts. I may try adjusting the limit screw and see if that > helps. > > I've thought about emailing Mark at RBW to see what he thinks. Also, > I've thought about emailing Jan Heine, as I'm sure he has some > insights. > > > > Just a thought as I hate when people blame their weight and then offer > up > > something like 185lbs. > > While 185 isn't necessarily clydesdale for my height (5'11.5"), it's > still heavy enough to flex the frame I think and possibly be a > contributing factor. > > > Cheers, > > Scott (now I feel horrible at my 225lbs) Henry > > Dayton, OH -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To view this discussion on the web visit https://groups.google.com/d/msg/rbw-owners-bunch/-/1Y3q7xAJ3f8J. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
