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Old 12-17-2016, 06:49 PM
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Quote:
Originally Posted by X53Jay4.8is View Post
Okay got it. When I think of structural I am under the impression that the without it the structure is going to fail during use. So without this stiffening plate will the structure of the X5 bend and twist thus making it unsafe to operate or is it just there for more added support?
I'm guessing now but I would say that as the sub-frame is tubular steel with welded junctions, the reinforcing plate is to reduce the stress on those "corner welds" when the sub-frame is subjected to twisting (torsional) forces, like entering a driveway at an angle etc.

Welds on tubular steel like this are very strong when compressed or stretched but not when twisted; the steel tends to fracture on the tube body along the weld line (the weld is often stronger than the thin-walled steel tube).

Lean way back on the rear two legs of a welded steel chair for a bit and see what happens...

Now bolt a square piece of thin alloy sheet to the legs on one side (or both), using four bolts and see if you can lean back for longer. The thin sheet will prevent the "square" steel frame from becoming a parallelogram, breaking the welds and collapsing. the sheet doesn't have to be thick, as all the forces are in the plane of the sheet. Just like on the E53... Need good bolts though (able to withstand high sheering forces), also like on the E53.
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2005 BMW X5 3.0d (b 02/05)
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