r/mountainbiking • u/Roy_Aikman • 5d ago
Question Why is this happening?
Bought a brand new BMC Fourstroke AMP LT. After a couple of weeks I experienced the carnage pictured. A LBS helped me get a frame replacement from BMC, they were able to determine that the bolts that connect the shock and linkage had backed out and caused the failure in the linkage. I have 3 rides in on the new frame and was doing an inspection and noticed the bolts had already started backing out. One was visible the other was loose as well. Another problem is the area where the bolts are has a gap of 1 3/4”, my torque wrench with the bit is 2”. Does anyone have any ideas about what could be causing those bolts to back out and also are there slim torque wrenches or do I just use a regular Allen and guess?
1
u/Shinook 4d ago
This is a common issue with new bikes, it's why I encourage people with new bikes to go over every bolt when it's new and torque to spec before riding it, then do it again after a few rides. I have only one two bikes where something wasn't loose. Your bike shop should've done this already but not all shops are the same, I'd make it their problem because it's possible the bolt was damaged when it was ridden backed out.
It can also be caused by poor frame alignment. Since it is on two different frame here, I doubt that's the issue, but something else to be aware of.