JFryer Posted February 12, 2003 Share Posted February 12, 2003 Anybody know the how stiff the suspension techniques 3/4" rear bar is compaired to the stock early 260Z 20mm Bar. The ST bar that I am talking about is the one that mounts behind the uprights. Which makes a direct comparision hard due the differences in arm length. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 12, 2003 Share Posted February 12, 2003 If you do the math (ignoring the lever arm lengths): 1" = 25.4mm 25.4mm * .75 = 19.05mm 3.14 * (20*20*20) = 25,120 3.14 * (19*19*19) = 21,537 25,120 - 21,537 = 3,583 3,583 / 21,537 = 0.166 The 20mm bar is about 17% stiffer then the 3/4" bar. That's assuming I've got the calculations correct. Quote Link to comment Share on other sites More sharing options...
Guest Thurem Posted February 12, 2003 Share Posted February 12, 2003 Jeremy and John From Herb Adams "Chassis Enginering" book, I've gathered: The stiffness of a rollbar is a function of the diameter raised to the 4'th (not the 3'rd ) power. The easiest way is to compare the relationsship between two bars ie. a 19mm and a 20mm bar it would look like: (19 / 20)^4 = 0.815 So a 19mm bar has 81.5% the stiffness of a 20 mm bar. If you divide the stiffness by the swingarm length (provided the swingarm don't flex), you get the overall stiffness. Again I like to compare the relationship between two bars best. So for arguments sake the 19mm bar has a 40cm (400mm) swingarm length and the 20mm bar has a 50cm length. Then you can compare the two arms like this: (19 / 20)^4 * ((1/40) / (1/50))=1.018 So the 19mm bar with the shorter swingarm is 1.8% stiffer than the 20mm bar with the longer arm. To easily grasp the effect of the swingarm length just think about a short wrench versus a long wrench, it is harder to loosen a nut (twist a swaybar) with the shorter wrench. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 12, 2003 Share Posted February 12, 2003 Yeah, I was pretty sure I had the math wrong after I made my post. I was trying to find the calculation in "Race Car Vehicle Dynamics" but I obviously picked the wrong one. Quote Link to comment Share on other sites More sharing options...
JFryer Posted February 12, 2003 Author Share Posted February 12, 2003 Thanks I guess the real ? is how long is the lever arm on the ST sway bar. I went out and measured the stock one at 31cm. So if somebody could post the length of the ST arm I will work the math. Quote Link to comment Share on other sites More sharing options...
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