Fork Brace Application and Potential Install Modification Question?

The Standard

XS650 Addict
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Los Angeles
Adding a Circle Industries style fork brace on 34mm front end - '72 model bike.

On the topic about fork stiction and the brace being installed should have a slip fit between the fork lowers. If the brace being installed is too wide or narrow as-is, can it be widened or narrowed at the mounting portion off the bike to shape it to the slip-fit spec? Or does that compromise the brace's structural rigidity and performance afterwards? Brace is aluminum.

Other thought is if brace's exterior mounting surface is narrower than the fork tube mounting hole face, to shim difference with washers or an aluminum spacer. Won't look as good but would this functionally work without taking away from the brace's intended added performance?

My measurement of fork lower spacing (inside face mounting holes across) is 5-1/8". The fork brace I have is 4-1/8" wide at the fork lower section mounting holes section. As seen in the picture, the brace has more of an upside down "Omega" shape that "U" with straight or 180 degree, vertical profile. Would opening the span of the brace and straightening one or both lower mounting sections for a slip-fit at 5-1/8" weaken the brace or not relevant the way the brace works with keeping lowers from rotating?

As being new to how these work in improving front fork performance, I have heard they keep the forks or lowers from rotating and also keep the forks from flexing outside of the parallel track down from the upper and lower triple clamps. The latter makes sense to me but I do not follow the part about it keeps the forks or lowers from rotating?


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    circle industries brace.png
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Your axle stops the forks rotating. The guard is a brace, the Special guards have extra material between the mounting points under the guard for better bracing. Removing the guard, (some like to add a brace with a guard), a brace is required to stop the forks from walking, so to speak. Imagine the forces on the forks where the inner goes into the outer tube when the forks are fixed at the top and bottom. The only thing that is stopping them from bending, where the 2 meet, is your seal, that is where all the forces are when riding and especially when braking

Over a period of time front forks, (Inner tube), get bent from normal riding. It is a thought the single brake rotor on the fork contributes to a bent fork because all the topping power forces are transferred unevenly to the one fork
Not a fork engineer but I'd be carefully working the brace till the flanges are at 5 1/8" and parallel horizontally and vertically, while keeping a nice round shape to the arch. 1/2 thick spacers, longer bolts will cost you rigidity. Anything other than parallel and the right spacing and you'll be introducing binding.
To be assured the fork brace mount spacing is correct which is critical, the front wheel, fork top caps and springs should be removed. Bike on a support under the front engine mount works.
The fork sliders should slide up and down without binding before the brace is installed individually and then the sliders should slide up and down together with a similar feel, not binding with the brace in place loosely. Then the brace can be tightened in that position.
An improperly mounted fork brace will cause both fork seal and fork action problems. Worse than not having a brace at all .
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brace is required to stop the forks from walking
If you have the necessary skill, grab a handful of brake while the bike is heeled over in a corner. Pull it down some, then release the brake. If your line changes, then a fork brace will be of benefit. If your line doesn’t change, you don’t need a brace. If you can’t run such a test, you probably don’t need the brace. JAT