You point out correctly that the CX70 cage is narrow up top and wider down low. The right question to ask is why? The reason is front index shifters (brifters). They click into position, and have a little trim mini-click. The derailer has to be precise, because the shifter positions are limited. For those of us that use friction shifters, it is a little annoying because of the amount of trimming we need to do. With friction shifters we don't really need a narrow cage. Pretty much any old road bike front derailer (from the early 1980s up to the beginning of brifters) has a nice wide cage, and will shift your compact double really well.
For those of us stuck with a narrow cage front der wanting to make the best of it, you can gently splay the upper cage open with a little crescent wrench or similar. Mechanics used to tune front derailer shape all the time as part of a build. You can get yourself a bunch of extra room, and it's hard to ruin it completely. The other nice thing about classic older front derailers is that they are often really cheap, and they have a longer lever arm, so they need more cable pull. That makes them less sensitive to your trim movements, so you feel like you have finer control. Nice wide cage triple front derailers, particularly ones with a good shape to follow our smallish chainrings and not hit the chainstays on our large BB drop bikes, are rare. That's why Riv bought up literally hundreds of Campy front derailers when they had the chance, and why lots of us will never let ours go. New, orderable front ders that fit ideally on Rivendells are few. They (Riv) are always on the lookout, because it's a challenging piece. They do their absolute best with whats available. On Friday, September 4, 2015 at 4:27:48 PM UTC-7, David Person wrote: > > Normally, when I set up a front derailleur I follow Shimano's > recommendation about having 1-2mm of clearance between the large chainring > and the derailleur cage. This has always worked will for me, resulting in > crisp shifting. Since building up my Sam Hillborne back in June I've been > running the CX-70 derailleur at this height but find I have to constantly > trim the derailleur to keep it from rubbing the chain. At this setting I > can only get a few shifts on the rear before having to adjust the front. > Quite annoying. I primarily use the large chainring, doing most all the > shifting on the rear, so having to constantly trim the front was getting > old quickly. Another issue was that there was little room for adjustment > between the inside of the cage rubbing and the outside of the cage rubbing. > I notice that I didn't have the same problem when on the small chainring. > Then I noticed that the front of the cage is a lot narrower than the back, > and when on the large chain ring the chain is positioned between the cage > near the front, while the chain ride between the cage more toward that > middle to rear when on the small chainring. So that got me thinking that > perhaps raising the derailleur up a bit would give me more clearance > between the sides of the cage when in the large chainring, with affecting > the shifting too badly. So today I raised the derailleur to that there is > 7mm of space between the large chainring and the cage. I'm happy to report > that this has made a huge difference in my enjoyment of riding the bike. I > can shift 5-6 cogs on the back before I have to touch the front shifter to > trim the derailleur. And when I drop the front down to the small > chainring, with the chain on the rear cluster anywhere from the middle to > the largest cog, there is no need to readjust the front to keep the chain > from rubbing the cage. Pure heaven. And the shifting performance has not > suffered either. Now granted, I don't ride this bike in a peloton of > riders, inches of the wheel in front of me, where every shift is critical, > but I've not noticed a decrease in the crispness of the front shifts. > > Thought I'd put this out there in the event anyone else was suffering with > the same issue. > > David > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
