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Thu, 02 Nov 2006
Apparently Rocky Mountain Element bikes will break if you have low shock pressure. - 16:40
So as stated below my Rocky Mountain Element 50 Dual Suspension frame broke while out riding on Friday morning 2006-10-20. As the frame snapped just below the shock mount I just looked at and though, ahh well something was wrong there, they will replace it under warranty. The warranty says 5 years for dual suspension frames. Of course it also says under what is not covered "B.Consequential damage or any damage caused by accident, misuse or abuse." and "C.Improper assembly and/or lack of proper maintenance," and there is the other clause that the majority of bicycle manufacturers seem to place in their warranty now days under What will void your warranty "A.Competition racing".
Anyway as you may suspect this is leading up to the Australian Importer of Rocky Mountain (Advance Traders) have rejected the warranty claim, Rocky Mountain are standing by the call Advance Traders have made. Their reason for rejecting the warranty claim is that the shock pressure was too low when it was bought into the store. I have been running the shock at 150 psi since I bought the bike. I can not remember exactly why I chose this pressure, though mostly it was from riding it, looking at how much it sagged, checking to ensure the shock was not bottoming out while riding (tie a zip tie around the shock shaft) and setting it to the pressure that seemed to give about 1 inch sag and felt comfortable.
Rocky Mountain have since said the pressure should have been around 190 psi for someone my weight. However I am trying to work out why a low pressure in the shock would cause the frame to break. What Advance had to say on this was somewhat hard to interpret.
You are correct in saying that a standard triangle frame should not break in the middle of the tube, which would probably be a sufficient point if the bike were a hardtail. But, because you have a moving rear end, it's highly likely that excess force (due to heavy impact and / or undersprung shock) through a certain area will cause the problem you have experienced. "The key to it's design is that it doesn't rely on the shock as a structural component of the suspension." (Rocky Mountain 2004 catalogue - Element - Design). If the shock were a structural part of the design I would expect the shaft of the shock to bear the brunt of the force and bend, or the shock bolts to do the same instead of the force being transmitted through the frame.
So they do not even answer my query as to why a low shock pressure will cause the break, it seems they suggest it is highly unlikely to cause the problem I have experienced with a moving rear end. I have asked in my email why the low shock pressure would cause the break. There is nothing in the warranty or owners manual suggesting the frame is in grave danger of breaking with low pressure in the shock. Also the claim made that the warranty guy at rocky mountain has never seen a frame break there before, I think would suggest there must have been something wrong with this specific frame.
The price they have offered a replacement front triangle to me is AUD $750, however I still do not understand why the low shock pressure is being used as a reason for rejecting my warranty claim. Anyway links to parts of this page are at the top to make it easier to see different things I have written about here.
I am not an engineer so I am waiting for some feedback from friends who are to see what someone who knows about this stuff would say on the issue. It is interesting to note that no onw from either the importer or Rocky Mountain have looked at the frame or seen it themselves. They are basing the rejection on photos I took and on asking the bike shop I some questions about it.