Originally Posted by
reppans
Anyone have any problems with their racks or rack mounting points (screws/braze-ons/etc) under these loads on rough terrain? Looks like some of you folks have put big miles on rocky dirt roads with a lot of unsprung weight - just wondering how these mounts hold-up to the constant hammering, particularly the rear racks which seem to carry all the weight on a single screw/braze-on per side.
Thorn rates their expedition rack at 60 kg when M6 bolts are used, but when M5 bolts are used they cut that to 40 kg. And, they say cut those weight ratings in half on South American Ripio. But I run a Tubus Logo rack (rated at 40 kg) on the rear of my Thorn bikes, not the Thorn expedition rack.
Keep in mind that on a pretty rough road, you are likely riding pretty slowly. That said, I was on several roads last summer where there were so many cobbles that I quit trying to miss them if they were smaller than tennis balls.
The bike in this photo, I use M6 rack bolts, it is a Thorn Nomad. I am not aware of any bikes other than the Thorn Nomad that comes with M6 rack mounts as standard. My other touring bike that I mostly use on pavement has M5 bolts like virtually all other bikes.
Over the years there are occasional discussions of high strength bolts on this forum, but I have generally just used the standard stainless bolts available at most hardware stores.
I have observed several people that have lost bolts from vibration, not failure from insufficient strength. I always recommend blue loctite on rack bolts.