here's a rear view of the Suntour <http://img.photobucket.com/albums/v728/bulldog1935/Raleigh/700c/aP1170010.jpg>
here's a rear view of the Shimano 600 <http://img.photobucket.com/albums/v728/bulldog1935/Raleigh/F%20Moser/aP5190022.jpg> the corner that started the crack is the upper, just behind the parallelogram. If you look close, you can see how the section is reduced there on the Shimano. On Saturday, January 24, 2015 at 5:00:50 PM UTC-6, Ron Mc wrote: > > I can't copy the image to write on and show you how the fracture > progressed, but it started at that acute corner. I compared the designs of > 4 other derailleurs. Campy Chorus, Suntour Cyclone GT, Shimano 600EX and > Shimano Ultegra 6500. > Both the Campy and Suntour have twice the metal at the same point, so it > would take 20,000 lbs to shear either there, and all the stresses are cut > in half compared to the Shimanos. > Neither the Campy or Suntour have that same acute point - both are > 90-degree + rounded corners. > Both Shimano derailleurs have the same reduced area (for weight reduction > and probably a bad stress location for it. > Both generation Shimano derailleurs have the same acute angle at that > location. > Again, at least a questionable design in comparison, and probably an > unlucky piece of "dirt" in the casting. > > On Saturday, January 24, 2015 at 4:26:28 PM UTC-6, Ron Mc wrote: >> >> It would take about 10,000 lbs to sear that fracture area - you can't do >> that on a bike. The failure most likely resulted because of the sharp >> corner that could not tolerate just the wrong, but normal, casting >> segregation in just the wrong place. It occurred over time until the >> reduced uncracked area small enough that you could shear it with normal >> bike riding loads. It's also possible an impact load could have started >> the crack, but that would require examination in an electron microscope to >> verify. If you want to send it to me, I can tell you. >> >> On Saturday, January 24, 2015 at 8:04:08 AM UTC-6, Ron Mc wrote: >>> >>> I analyze fractures as a professional. The photos clearly show that the >>> thick part of the fracture and progressively cracked from both sides before >>> the area was reduced enough to let it pop - it's a fatigue failure, and >>> it's been going on a long time. TX PE No, 75665 >>> >>> On Friday, January 23, 2015 at 4:28:56 PM UTC-6, Bill Lindsay wrote: >>>> >>>> A completely not-bent derailer tab would definitely suggest that the >>>> derailer just decided to explode itself into bits on its own, which is >>>> indeed WEIRD. JRADSA = Just Riding Along Derailer Self Immolation >>>> >>>> On Friday, January 23, 2015 at 1:20:15 PM UTC-8, John wrote: >>>>> >>>>> Since I didn't see it happen, I have to do my best to understand based >>>>> on the after-effects. I was riding in some sticky mud at the time, but >>>>> there was no mud on my chain or on the derailer. I took the photo >>>>> without >>>>> cleaning the RD. It's a bit greasy, but no mud or rocks or sticks were >>>>> involved as far as I can tell. I was JRA (love that acronym) and it >>>>> appears as if the derailer broke in two, flopped around the chainstay >>>>> still >>>>> attached to the cable, and jammed the wheel to a stop. I'll be checking >>>>> the wheel for damage, but the derailer hanger is definitely not bent or >>>>> damaged. The small half of the derailer was still securely bolted in >>>>> place. It's weird, I tell you. Just WEIRD! >>>>> >>>>> I bought a better Shimano RD at Harris Cyclery during a business trip >>>>> to MA this week. I'm hoping it fails in a more graceful manner after a >>>>> long life. >>>>> >>>>> On Thursday, January 22, 2015 at 1:56:10 PM UTC-6, Bill Lindsay wrote: >>>>> >>>>>> I'm curious about the CAUSE and the EFFECT. Which was it: >>>>>> >>>>>> A. Did the derailer just separate into two parts on its own? Then >>>>>> the broken off part got caught in the spokes, causing you to lurch to a >>>>>> stop? >>>>>> >>>>>> Cause: Derailer fell apart on its own Effect: Broken bits fell >>>>>> into the wheel >>>>>> >>>>>> B. Did your derailer get caught in the spokes while you were riding? >>>>>> Your wheel ripped the derailer in two and you lurched to a stop >>>>>> >>>>>> Cause: Spokes grabbed derailer Effect: Bike lurched to a stop and >>>>>> the wheel broke the derailer >>>>>> >>>>>> C. Could something else have gotten into your rear wheel, like a >>>>>> stick? >>>>>> >>>>>> Cause: Stick in the spokes grabbed the derailer. Effect: Bike >>>>>> lurched to a stop and the stick broke the derailer >>>>>> >>>>>> Getting the rear der caught in the spokes is not uncommon. The >>>>>> result is usually a busted derailer and often a badly bent derailer tab. >>>>>> Derailers randomly commiting suicide by exlpoding themselves into two >>>>>> parts while JRA (just riding along) is not common. >>>>>> >>>>>> On Sunday, January 18, 2015 at 2:56:14 PM UTC-8, John wrote: >>>>>>> >>>>>>> Towards the end of my ride today, I heard a loud crunch and my Ram >>>>>>> lurched to a stop. Didn't take long to figure out the cause. My >>>>>>> Shimano >>>>>>> Tiagra RD had separated into two pieces. The larger chunk with cable >>>>>>> attached wrapped around the right chainstay and lodged in my spokes. >>>>>>> The >>>>>>> other piece remained bolted to the dropout. Fortunately, I was going >>>>>>> very >>>>>>> slowly at the time, so no damage was done to my wheel. I wasn't >>>>>>> shifting >>>>>>> at the time, just pedaling along. I was able to break the chain and >>>>>>> remove >>>>>>> the cable so I could at least roll my bike to where my wonderful wife >>>>>>> rescued me. Surprising because the RD is only a couple of years old >>>>>>> and >>>>>>> has not suffered any tip-overs that might have damaged it. I took a >>>>>>> couple >>>>>>> of pictures of the fracture: >>>>>>> >>>>>>> https://www.flickr.com/photos/53546004@N07/16312803255/ >>>>>>> >>>>>>> https://www.flickr.com/photos/53546004@N07/16125257318/ >>>>>>> >>>>>>> Is it just me, or is this not uncommon? >>>>>>> >>>>>>> Off to shop for a new RD. >>>>>>> >>>>>>> John >>>>>>> >>>>>> -- 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.
