I've been studying these a bit lately too, and come to the following conclusion: https://twitter.com/FredCookeNZ/status/ ... 7740062720
Which is a disappointing one, to say the least.
So, what form should they take? What style should they NOT have?The Good
What it's like when it's right and doing a good job of keeping the suspension geometry aligned.
- Straight across, in BOTH axes!
- Low down to strut top plate and/OR
- Strut top plate bracket and fasteners must be rigid and strong
- Light weight bar - no bending moments, only compression/extension
- Triangulation to firewall centre IF sufficiently far away and not otherwise - in fact, if the strut towers are very close to the firewall, why bother at all? :-p
Seems easy, right? Seems not, if you look around...The Bad
What it's like when it's bad and not doing much except adding weight. In order of popularity! :-p
- Bar is bent in one or both axes. Fail. Not stiff, likely to allow the movement it was designed to prevent. Purpose not achieved. Very popular failure...
- Bar is a frame, hugely overbuilt, not light, commonly combined with the above for maximum irony.
- Strut top plate brackets inherently weak  from insufficient plate coverage. Eg, plate 200mm wide, brackets only pick up half of this, or less
- Strut top plate brackets inherently weak  from insufficient triangulation/strange angles
- Triangulation added to firewall when angles are very shallow - minimum benefit, if any, likely an overall loss for the weight
- Triangulation picks up weak area on firewall that can't support anything - no benefit, possible damage
And there's just acres of these bad strut braces around. Unlimited choice, as we'll see when the images start rolling in.Reasoning
If the bar is bent it cannot be stiff. This one's obvious, despite being the biggest failure. To have it stiff/strong after being bent it would need to be high/thick. It can't be, there's an engine in there somewhere, and a bonnet/hood above.
If the distance from the bottom of the strut top plate to the attachment point is half the lateral distance from the outer most strut stud to the inner most strut stud, you're going to experience 50% of the lateral force lifting up on your nut trying to strip the thread. Whereas if the bar mounts down on the plate very close to the surface, then the force is purely in sheer, and counteracted by the friction joint held in place by properly fastened nuts. If the height is the same as the stud spacing, the force is equal. If there's any point in using a strut brace at all, then this force could be significant and you don't really want it trying to break/loosen your fasteners.Challenges
Something must be motivating these failures, right? It's pretty obvious again:
- Engine is high
- Strut tops are low
- Bonnet/hood is close to strut tops on the outside/low on the outside, and bulges over engine in the middle
In the third case, there's nothing much to do except put the bend in it and hope it does something. Except maybe triangulating into the firewall instead/as well.
In the first/second cases, one can raise the mounting points on the top plates in a rigid and strong fashion and run something straight, or close to straight.
The compromise between sheer loads with a non-stiff/bent bar and levering loads with a straight bar up high would need to be made on the basis of calculations and/or actual testing. So now I'm wondering "Who am I to assume those calculations have not been made?", which is probably a fair synopsis at this point.
Post pictures of strut brace setups you consider good/bad and your reasoning why. I'll drop some in as I feel the need, but not right now as I need to make some progress on some other stuff.
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