Are the rings worn and while the CX70 allowed you to get by "normally", the 105 does not ? Different cage dimensions and all that.
On Tuesday, May 26, 2026 at 4:04:08 PM UTC-4 Tim wrote: > I changed the FD on my 650b rando bike (my only non-Riv). It's set up with > Ultegra brifters with a Rene Herse double crank. The old CX-70 FD wasn't > working well anymore so I swapped to a shimano 105 FD. The derailer shifts > much better but now when I shift from big ring to small ring the chain now > falls between the chainrings. It did this immediately upon my first ride so > I took it to my LBS thinking I had installed the derailer wrong, although I > kinda mostly know what I'm doing. When I went back they told me that my > crank was bent. The mechanic said he even asked his boss and he agreed. He > went on to explain to me that the Herse crank only had 3 bolts connecting > to the crank where most cranks had 5 and he insinuated that the RH was > weaker because of this, and that it was one of the bolt "tabs" that had > bent. . > > I was very skeptical as the problem had never happened in the 10 years > I've had this bike (It's a custom and came to me mostly assembled) and I > have never crashed the bike. I brought the bike home to remove the crank > and disassemble to check it out as much as i could. I removed the arms from > the bike, removed the chainrings, cleaned the crank and reassembled. Th > chainrings seemed flat when I laid them on a flat surface. I reinstalled > the crank and on the first downshift on the bike stand the chain fell > between the chainrings. > > I emailed Rene Herse and their answer was that you can't bend a crank by > pedaling it and that the FD is the introduced variable that has caused the > problem. I must say that I completely agree that the only change made is > the one that caused this problem but I don't at all understand how or why > the derailer would immediately cause this problem. So therefore I don't > know what to do to fix it. > > Any thoughts? > > Peace, > Tim > -- 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 [email protected]. To view this discussion visit https://groups.google.com/d/msgid/rbw-owners-bunch/aac7143b-b08b-4eef-b6a2-f679ca424e88n%40googlegroups.com.
