Ralle-Moto F800GS Shock Bolt Bracket

Discussion in 'Vendors' started by davidpetersen, Feb 11, 2010.

  1. davidpetersen

    davidpetersen BestRest Adventurer

    Nov 19, 2001
    Seattle, WA
    Got an F800GS? Read the 60+ page thread about the rear shock bolt failures? Seems that under certain conditions, the upper rear shock bolt can bend, which in turn bends (and ruins) the frame.


    You can find the thread here. Bring popcorn and a pillow, it'll be a long show.

    There's a simple, bulletproof fix: The Ralle-Moto F800GS Shock Bolt Bracket.

    The billet aluminum bracket prevents the bolt from bending, and reinforces the entire shock mounting system. Price is $100.

    They are on the shelf NOW and ready to ship.

    Order here: http://www.bestrestproducts.com/p-259-ralle-moto-shock-bolt-support.aspx


    A few comments I've posted regarding this bracket:


    Here’s what we know:

    The span between the center frame tab and the right frame tab is 72mm. It’s a questionable design but we’re stuck with it.

    A 12mm Bolt spans that 72mm gap… The fate of Western Civilization rests upon That Bolt. If it fails, the frame fails, all is lost and we descend into the Dark Ages.

    Fitted onto The Bolt is a 30mm steel bushing (with a rubber cover), and a 42mm bushing which makes up the upper shock eyelet. This is the stock BMW setup.

    Properly torqued to 100Nm, The Bolt captures, confines, and compresses those components into an integral stressed assembly measuring 20mm diameter. In theory that 20mm shaft should handle the load of the rear shock bashing its way upward …

    But we know that the buttery soft bolts supplied to us by BMW have been bending. The actual cause(s) for their bending is hotly debated, which is why this thread is now 38 pages and growing.

    So how do we fix the problem?

    Proper Bolt torque is critical. 100nm.

    Confirm that The Bolt isn’t running out of threads inside the cylindrical nut, BEFORE it’s actually tightening the components into a stressed member. If The Bolt shoulder contacts the nut before proper torque is reached, you’ll get a false torque reading and the components won’t become a stressed member. Instead they’re just a series of loose spacers sliding on The Bolt. In that event, The Bolt will bend. Fit a washer under the head of the bolt, lube the bolt head, and that problem is gone. Thanks for that idea, Tom.

    A stronger 12.9 grade Bolt is available from TT. This is good stuff because it increases the overall strength of the stressed assembly. This assumes you’ve properly torqued The Bolt to 100Nm, and that you’re tightening the stressed assembly, not bottoming out on the shoulder of the bolt.

    Another solution is a clever one-piece, 20mm diameter, 72mm long, press-fit, full-length bushing, with needle bearings, thru which The Bolt passes. Because this bushing spans the entire 72mm gap between frame tabs, chances that The Bolt will bend are greatly diminished. You’d hafta bend a 20mm shaft which is unlikely.

    The above items will certainly improve The Bolt’s load bearing characteristics, but we’re still talking working on the problem of spanning that enormous 72mm gap between frame tabs. And the truth of it is that the tabs are perhaps a bit undersized and poorly placed to begin with.

    My Preference – Overkill

    From my perspective the best way to increase the strength of the entire upper shock mounting system and frame assembly is to fit the solid billet aluminum Ralle-Moto shock brace. Here’s why I think it’s the best, easiest, and quickest option.

    It fits with all known shock absorber upper eyelets. If the 12mm bolt fits thru the hole, the RM bracket will fit. No need for specialized bushings or other spacers.

    It’s available, on the shelf now, and its easy to install.

    It reduces the unsupported gap that The Bolt spans between the frame tabs from 72mm, to only 42mm. Let me explain how this happens…

    We know the gap between frame tabs is 72mm. The upper portion of the Ralle-Moto bracket is 30mm thick. Because of the way it’s mounted to the frame, the RM bracket becomes an integral member of the frame, which means it doesn’t just transfer the load to the frame tabs (like the stressed assemblies mentioned above), but it also transfers the load in a vertical fashion, into the main frame assembly.

    The RM bracket attaches to the frame at an anchor point several inches below The Bolt. This 2nd attachment point effectively turns the entire RM bracket into a cantilevered brace. Because the RM bracket is clamped to the frame with the same 10mm bolt that holds the main frame to the rear frame, this effectively converts the RM bracket into an element of the frame.

    Besides being bolted to the side frame rail, the RM bracket also cradles the underside of that huge tubular cross-over frame member. Any upward stresses from the shock are also spread across that tube.

    At the top, where the shock absorber eyelet fits onto The Bolt, the open gap has been narrowed from 72mm, to 42mm. Even when using the stock BMW bolt, it’s virtually impossible to bend it across that narrow 42mm span. Of course when I say “virtually impossible”, I must specifically exclude John Gil, whose riding exploits and frame-bending abilities have taken on mythic proportions. 8^)

    With the RM bracket in place we’re not relying on just The Bolt, or just the frame tabs to handle the stress. The shock loadings are now distributed to The Bolt, the two tabs, the side of the frame, and the huge cross tube. I call that engineering overkill. I like it. Now I can worry about other things.

    Some have expressed concern that the RM bracket actually makes the upper shock mounting TOO STRONG. Perhaps there’s some truth to that. If you make the upper shock mount too beefy, other pieces might fail, like the shock itself. I’d rather replace a shock, than a frame.

    This photo shows that the width of the RM bracket is the same as the stock BMW bushing, rubber covering removed.

    This photo shows the open span for the upper shock bushing.

    This photo shows the RM bracket in place, and illustrates the way it has been bolted to the frame so that it becomes part of the frame itself. The nut on the end of the lower 10mm bolt is my own addition, the result of foolishly stripping the threads after installing it for the 20th time. (on-off-on-off for photo shoots). Normally that bolt threads directly into the aluminum block, no nut on the end.

    This photo shows the bracket itself, and helps you understand the mounting points and the way it cradles the large cross frame tube. The threaded bolt in the middle is my own addition; it is not normally part of the bracket.

    This photo shows the RM bracket bolted into place. The small bolt in the middle is my own addition. It fits into the hole that originally held a plastic zip-tie fitting, and was just calling for a secondary bolt to be threaded into the RM bracket.

    So there's my $.02 worth. Consider the source, I'm a vendor that sells the RM brackets. But putting that hat on the shelf, I think the boyz from Australia have come up with the best system to eliminate the problem.