bjhines Posted February 13, 2007 Share Posted February 13, 2007 Before you go and find your calculator... The type of tubing and the way it is formed will greatly affect it's performance... You need a lot of information about specific tubing types... The other issue is that you have only a general idea of how much force will be applied... this will vary from car to car depending on chassis modifications, spring rates, tires, overall weight and balance, brakes, engine power, driveline mounting, suspension geometry, track surface, etc., etc., etc.... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 13, 2007 Share Posted February 13, 2007 I've always wondered what exactly the force was on the bar. My 1" OD aluminum "tap tube" with 5/8" rod ends seems to be holding up fine though, and it is light... Quote Link to comment Share on other sites More sharing options...
heavy85 Posted February 13, 2007 Share Posted February 13, 2007 Even a straight bar will bend under enough load. It will not crush, like an aluminum can, even if the loads are perfectly aligned along the bar's axis. I cannot remember why this occurs I believe it has to do with buckling vs yield and typically bucking is only a concern with very small t/r ratios (thickness/radius) such as in an aluminum can. By the way stiffness is inversely proportional to t/r so large radius and thin wall is the stiffest. This is where you have to consider buckling to determine the practical limit. Cameron Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted February 13, 2007 Share Posted February 13, 2007 ::scratches head:: Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted February 13, 2007 Share Posted February 13, 2007 ^^^ I think Cameron is speaking in generalized terms... a larger diameter thinner-walled tube will have less structural flex than a smaller thicker-walled tube given the "same amount of material" per linear foot. However, at some point, the thinner-walled tube becomes structurally unstable. In any given environment, there is a "happy balance" between wall thickness and tube diameter with regards to the best compromise between flex and crush points. EDIT: No.. I'm not an engineer. No... I'm not edumacated in this field. But this is the only thing that makes sense to me. Quote Link to comment Share on other sites More sharing options...
Guest Mike Posted February 13, 2007 Share Posted February 13, 2007 ... in other words a solid or very thick-walled tube "bends or flexes" while a larger diameter thin-walled tube "buckles or crushes". There is always a "best compromise" between diameter and wall thickness for a given material and application. Quote Link to comment Share on other sites More sharing options...
dimsum Posted February 14, 2007 Share Posted February 14, 2007 Before you go and find your calculator... The type of tubing and the way it is formed will greatly affect it's performance... You need a lot of information about specific tubing types... The other issue is that you have only a general idea of how much force will be applied... this will vary from car to car... All of this is true. It's difficult to calculate the exact amount of load and determine the optimal bar diameter and wall thickness. I'm sure most aftermarket companies just make something that is way thicker than necessary, so they don't have to crunch numbers. Other than using a stress/strain gauge, I'm not sure how to calculate the loads applied to the strut tower bar. However, it is fairly easy to look up the modulus of elasticity for the type of metal you plan on using. Some web sites will even give you specific numbers based on how the tube was manufactured. Quote Link to comment Share on other sites More sharing options...
dimsum Posted February 14, 2007 Share Posted February 14, 2007 My brother and I always wanted to replace a strut tower bar with one fabricated out of wood or another material that would permanently deform when placed under stress. We could take the car out, drive for a bit, and see how much load the car actually places on the bar. If the wood cracked, or even shattered, it should show an example of how much compression or tension the bar had to endure. This is probably something best done with the rear bar, so if it does shatter or splinter, little pieces wouldn't get into moving parts. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 14, 2007 Share Posted February 14, 2007 That has been done before. I believe katman used a tattle tale dial indicator and tested the deflection. I've read an article where the same was done with a Porsche 944. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted February 14, 2007 Share Posted February 14, 2007 We could run a string tight between the two rear strut towers (or the front if you want to drive around with the hood off) and have your passenger watch the string as you run the car through some hard corners. That would at least give us an idea of how much movement we are trying to stop. I'd do it, I can't push my car around corners fast enough to flex the body.....have to wait till I get the motor back together. Quote Link to comment Share on other sites More sharing options...
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