I am not convinced that rd cage length is the culprit here. The extra length is from the pivot to the lower idler wheel isn't it? The top idler wheel is in pretty much the same place and thats the one driving how the chain comes at the cluster. What mechanism do you think causes the long cage models to be less precise?
On Aug 25, 4:46 am, Michael Hechmer <[email protected]> wrote: > Out riding on my Rambouillet yesterday, which has Silver DT shifters, I got > a ghost shift. This happens rarely, every 35-50 miles or so, enough that I > usually just chalk it up to user error. But this time I got to thinking > about why this works so well for me while others have so much difficulty. > > I have four bikes with Silver shifters, my Ram and old racing bike have DT > shifters, and two touring bikes, an Ebisu and an old Trek have BE shifters. > I realized that I do seem to have some more issues with the touring bikes, > ghost shifts every 10-15 miles. This is annoying, but not enough for me to > want to give up either 9 speed or friction. For a long time I thought the > difference seemed to be in where the shifters were located and wondered if > I got more cable stretch, and noticed that the BEs have a tendency to > loosen the D ring a bit. But yesterday I realized that the placement of > the shifters has nothing to do with the difference in performance. > > To make 9 speed friction work I always use good cassettes, good chains and > good deraillers. All four bikes have hi end cassettes and conex 908 chains, > kept clean and replaced when needed. The difference in performance that I > am seeing is in the derailler. The two bikes with DT shifters have compact > doubles and relatively short range deraillers - Ultegra 6700, which is a > short cage derailler designed for CDs & the standard 6600 derailler > designed (I think) for 29 teeth. Both of these work well across the 31 & > 29 teeth of the two bikes. The touring bikes have triple cranks and a 38 > tooth range, which of course requires a derailler with a much longer cage. > I use the Ultegra racing triple derailler on one and a mid length Centaur > on the other. These cages are much shorter than the mt bike deraillers, > like the XT, and very long cage Centaur, which are designed for 45 teeth > or more. It seems obvious to me as I think about it that as the cage gets > longer the possibility of mis-allignment gets greater, which is what causes > ghost shifts. > > So, it looks to me, that to make friction work well with 9 speed the bike > should have good components and the shortest cage that will work with the > gear range needed. I have found that the mid range deraillers will handle > my set up (48/34/26 & 12-28) with some occasional failures. I expect that > riders who want an even wider range will have increased ghost shifts if > they use friction. > > Michael -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
