Thorn Cycles Forum
Technical => Luggage => Topic started by: Blue lotus on September 24, 2014, 04:04:44 PM
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Hello all,
I bought (through SJS) and fitted an Axiom StreamLiner Road DLX Rear Rack (http://www.sjscycles.co.uk/axiom-streamliner-road-dlx-rear-rack-prod28144/) on my bike as I thought its design was nice looking (streamline), but most importantly it is the only one that seem capable to take the heavy load of 50kg (!?!?!!). Price was OK.
I tried it the other week for a few days of cycling with some light-ish load (tent, mattress and sleeping bag on one side, clothes on the other), max 7-8kg on each side.
After the trip, I was surprised to find the lower screw of one side slightly loose (I'm sure I had it well tightened).
I need to try it out a bit more to check that but I am wondering if there is not something fundemantally wrong in its design. In particular that while moving, the moment (created by the moving load) applied on these screws is quite high due to the moment arm created by the lower bracket. This moment arm is hardly present on other rear rack design where all the load is applied vertically exactly on the screw. I am wondering if these screws are not meant to work purely in shearing, rather than extension/compression.
I look forward to seeing what your experience is with these racks if any, and your advice.
Regards,
Etienne
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Etienne,
i have a son who is good at stressing bike bits beyond normal.
He broke the odd bolt and managed to loosen the other lower fixing bolts of racks when cycle camping.
I got round this by putting longer bolts through the fixing points with a locknut to hold the assembly tight.
He never managed to break that setup...
Julian.
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Loctite is an obvious first solution.
I think the loosening is caused by vibration. Interesting that only one side (you don't say which) is loose, and that's where your theory regarding the "moment arm" has merit. This may be due to the vibrating arm acting counterclockwise on the loose side, and "righty-tighty" clockwise on the opposite side.
Julian's solution is a permanent fix, as long as you have room behind the mount point for the locknut.
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Hi,
To reply to your comments, the screw was undone on the left side (opposite to gears).
Putting a nut is possible on one side only, this side actually. I'll see how it behaves in the coming weeks without mmodifying anything. A few loads of milk, apple and orange Juice added to the usual weekly shopping should allow me to conclude on the case!
All the best,
Etienne
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PS: forgot to add that this bracket that I suspect of misbehaviour bring a big positive side to the rack: it puts it right back and give a lot of foot clearance.
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In particular that while moving, the moment (created by the moving load) applied on these screws is quite high due to the moment arm created by the lower bracket. This moment arm is hardly present on other rear rack design where all the load is applied vertically exactly on the screw. I am wondering if these screws are not meant to work purely in shearing, rather than extension/compression.
I'm not sure but I would think that if this was the case, it would be more likely to happen on the drive side. If there is any movement there would be more force when in the downward direction due to gravity, that downward force would be applied to the bolt in an anticlockwise direction on the drive side bolt?
Anyway, Loctite should sort the problem.
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I'm not sure but I would have thought that if this was the case then it would be more likely to happen on the drive side, if there is any movement there would be more force when in the downward direction due to gravity, that downward force would be applied to the bolt in an anticlockwise direction on the drive side bolt?
Anyway, Loctite should sort the problem.
Yes, I that's where I was headed before Etienne specified the side, although without seeing the setup, the theory may still be correct, just operating differently. ???
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Nothing can replace a good touring frame with long chainstays for carrying luggage IMHO. The rear-mounted brackets will give you greater heel clearance, but the load placement will cause greater handling instability from the extended movement arm of your load. The luggage weight causes "the tail to wag the dog".
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Not sure what sort of bike you are mounting it to, but there is this as an option (http://www.sjscycles.co.uk/thorn-for-rohloff-cast-end-2-x-m5-to-1-x-m6-stainless-dropout-adaptors-prod11703/?geoc=au) to convert to a 6mm bolt for better tightening/greater strength. Designed for Thorn Nomad and uses the two drop-out mount holes.