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post #32 of (permalink) Old 08-07-2013, 02:30 AM
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Focuz Aluminum Sway Bars, Metal Too Soft for Big Stiffness Increase

When I first heard they were aluminm, I thought it was a misprint. But they really are aluminum.

The sedan rear bars were 19mm, and the Hatches and Wagons were 18mm until about 2005, when all rear bars were 19mm.

Sway bars act like springs when you are in a corner. So the have a spring rate for when the car is in a corner. The problem I have is aluminum is it's not as stiff as steel. For two identical bars, the steel bar is 3.0 X stiffer than the aluminum, and the aluminum bar is .33 X the steel bar stiffness.

So assuming an 18mm oem bar, vs a 22mm steel bar upgrade. The stiffness increase is 2.2 X. But adjusting for the softer aluminum, your upgrade in stiffness is: 2.2 x .33 = .73 X, or a 15% softer bar.

I spoke to the vendor on Ebay. He confirmed it's aluminum, and as he also is a Mechanical Engineer, he said aluminum would not be his 1st choice, for the reasons I presented above. He said that he bought them for next to nothing, as a big batch, and can not reorder them. Sounds like someone, who did not know what they were doing, had these aluminum bars "forged" in presses designed for a 22mm steel bar. And then dumped the aluminum bars to buyer/seller guys, like in ebay.

The aluminum is much weaker than steel, by a factor of at least 3. I'd watch out for jacking up the car from the left rear or right rear frame support points, to avoid putting a permenant twist in the bar.

I discussed this with Robert (VTRman) who installed the Focuz 22mm bar, and he did notice a significant improvement. He did replace the worn rubber pivot bushings with stiff poly pivots, which would stiffen the ride a bit. I believe him, and if theory conflicts with reality, theory has to be re-examined. But the new piots may explain some of his improvement.


04 6S atx hatch
93 RX-7, 75 Trident

Last edited by KevinK2; 08-08-2013 at 01:21 PM.
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