Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 I think I'm in the process of building a car serious enough... Can't someone with some math skill (this precludes me) figure out what the actual loading would be? I *might* be able to figure that out but I think its more complicated than that... wouldn't the spring and shock rate be a factor? (its the reaction force right?). Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Jon, I started drawing this (instead of studying like I’m supposed to be) and quickly came to realize that it doesn't matter (at least with the perameters you gave). *IF* the spindle is in the center, then the loads are the same on each side. The only way they’ll be different is if there is an imbalance. So what imbalance are you concerned about? Friction, braking, accell, the pot-hole? I might be able to figure it out with more info. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Jon, The thing that I struggle with the most, with the track that you are on, and I think we've discussed it in PM, is that if you succeeded in making all the suspension components absolutely rigid (to reduce the longitudinal stiction) then all the mounts in the car have to be PERFECTLY aligned. If you succedded in that, then there can be NO flex in the chassis. If there is, then something else has to flex. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 29, 2006 Share Posted October 29, 2006 The spindle is in front of the strut. It is basically centered in the 5.5" between the two attachment points. The strut shaft is ENTIRELY behind the two attachment points. So I think you're right that the force is lessened, but it is not in line like your diagram shows. As to your other point, I think realistically none of these parts is so rigid that they can't flex. I think the control arm would flex first, then the strut housing itself. Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 29, 2006 Share Posted October 29, 2006 I have not yet experienced the bending J bar that you guy's have (guess I havn't built a serious enough car). In looking at the front design, I really didn't figure the rotational loads to be THAT high. The only reason is does rotate, as far as I can tell is becuse the BJ isn't centered up in the same plane as the TC rod. It is, however, close so I assumed the rotational loads would be minimal. Apparently, they are greater than I expected. BUT, I do believe it takes a VERY extreme car under exteme conditions to cause a problem with that design. I don't belive its the same as what we're talking about in the back. Bending the J-bar isn't going to happen often. I did it once and changed things a bit by adding a piece of metal to the bottom. Regardless, the J-bar isn't as good as using a double shear bracket and solid rod end. I think what bends this part is heavy braking and then hitting a FIA style curb or getting the car into the air and coming down under brakes. At least that was my experience. If you look at a number of formula cars from the early 70s and even some trans-am cars from the 80s and 90s they have figured all this out. I was trying to go the easy route and discovered that it isn't always as easy as it looks. The rear arms pictured about from the first version of the back of my car were tested and worked just fine. I didn't see any issues of bending the clevice or the attachment point. But since I'd already seen a problem with the similar joint in the front all this is changing to solid ends in double shear on the inside especially since I was going to double the HP/TQ. And since I did read the Carrol Smith books I owe him that much. And I will probably change the aluminum toe adjuster to a swedged steel part because it makes me nervous too. Although I've used the tubing for TC rods and tie-rods for a long time. I usually build new ones every other year. I had three reasons for wanting to do the rear arms this way. The first, which will sound silly to most, is to be able to quickly change rear toe. And before Johnc rips me a new one for that being stupid I would like to point out that it is an autox thing. By changing toe I can get more heat into the tires when it is cold. The second reason was to increase the installation stiffness and a side benefit I'm hoping for is reduced stiction. And lastly was to have an easy way to change squat/lift and RC positions. On the second version of the car this all attaches to adjustable mounts. All of this is easy enough to test if you have a porta-power and a pull ram. You do what is called a parasitic compliance test. To do this test you push and pull across the axle and note deflections versus force. The second is you push and pull longitudinally (front to rear) again noting defelction changes per load. These kind of tests will tell you a lot and give you an idea of what will most likely be the first thing to fail. This simulates how the forces are actually fed into the pieces. Not a mathematical proof but a nice old fashioned low tech way of measuring this before you do something stupid in front of your friends. It's much better to find something out in the garage where your emabarassment can be contained Cary Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 The spindle is in front of the strut. Opps I made an effort to calculate this out. I don't expect it to be exactly accurate, but I think its close enough for the purpose, just as 3g's is probably close enough... I come up with 189 LBS. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Thanks Cary. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 29, 2006 Share Posted October 29, 2006 Alright, that number is lower than I expected, but even so, if you were assembling the suspension and you had to push with 111 lbs of force to get the strut into the top mount, would that be a problem? It would certainly be a problem for me... Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Jon, Something was bugging me about my numbers... I went back and found an error. 189LBS should be more accurate. I edited the previous picture to reflect that. Sorry. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 29, 2006 Administrators Share Posted October 29, 2006 ..... I think what bends this part is heavy braking and then hitting a FIA style curb or getting the car into the air and coming down under brakes. At least that was my experience.... Cary SOOooo.. Cary. When you race are you Auto-ing or Moto-Xing the car, I can see it now. The next generation of “X†games, Cary M. and his double back flip with a half twist in a 240 Z… Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 29, 2006 Share Posted October 29, 2006 That's already been done in a Jame's Bond film If you hit the curbs wrong on Medford you can get a little air. And their have been times when that extra little tenth seemed like a good idea. Bent parts after the fact seemed to indicated it may not have been. Cary Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Cary, In your linked pictures, the rear (outboard, toe link) pivot is not substantially supported vertically. Jon doesn't seem terribly comfortable with the extra side loads this would impart on the strut. If I read you correctly, not only have you driven the car in that configuration, but you're also doing it again on the revised car? What are your thoughts on the increased side loads? Thanks, Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 29, 2006 Share Posted October 29, 2006 In your linked pictures, the rear (outboard, toe link) pivot is not substantially supported vertically. Jon doesn't seem terribly comfortable with the extra side loads this would impart on the strut. If I read you correctly, not only have you driven the car in that configuration, but you're also doing it again on the revised car? Just to set the record straight. The tube80 has yet to run under its own power. Hopefully this coming year. But the old design of parts have been statically tested. And we ran this configuration on a modified stock-type arm (toe-control link) on our old yellow Z for three years with no issues. I don't have the means to meaure side load on the struts. And to be honest I'm not all that worried either. What we have here isn't really much different than the front end of a FWD vehicle. I'm sure those have side loads too but it doesn't seem to be too big of an issue. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 30, 2006 Share Posted October 30, 2006 Well in the interest of making the car as stiction free as possible, it seems that it's very easy to avoid this additional side load on the strut, so why not avoid it? If you're building your own control arm, is there any advantage to building it this way vs the other? I would look at building the maximum stiffness and minimum friction if I were making a control arm. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 30, 2006 Administrators Share Posted October 30, 2006 Ok, playing devils advocate here. It seem like John is wanting to redesign the strut suspension in such a way as to eliminate any and all loads imposed on the strut shaft that induces stiction, or at least in the fore and aft plane? I’m sure a Lower Control arm can be designed that would not allow the strut shaft to endure any “fore and aft†loads therefore reducing stiction in that that way, but the time invested in engineering such a part, you have to ask yourself, how much less work would it have taken to just design a double A-arm or some other “non†stiction suspension design? Also, if you were able to design such a LCA to take all the “fore and aft†loads away from the strut shaft itself, the cornering loads will still be present inducing said stiction. Seems like a lot of work for how much possible gain in track times or tire tracking over uneven track surfaces? And you will still have the side loads from cornering inducing stiction. It seems from a design perspective that it would-be rather hard to eliminate or even reduce the already existent side loads presented on the strut shaft to a level that would reduce stiction to a level that makes enough difference to be noticeably effective. A strut by definition is “supposed†to take those sort of loads, and to design a suspension that doesn’t side load the shaft of the “shaft†itself, is another suspension design entirely, i.e. no longer Chapman or McPherson strut. To me, if the idea of keeping it a strut type suspension is the goal, wouldn’t it would make more sense to spend the time energy and money designing struts with reduced stiction such as installing linear bearings internally in the strut with low drag seals, or maybe pressure fed plain bearings like the main and rod bearings in an engine? (The pressurized plain bearing idea would add lots of weight and complexity with a fluid pump, hoses, etc. and probably isn’t realistic, but it might reduce friction induced from strut side loading.) If you were able to design a Chapman strut suspension that takes away “all†loads that induce stiction in the strut shaft, by definition, you would no longer have a strut type suspension. Then it’s back to the drawing board for a new suspension design… Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 30, 2006 Share Posted October 30, 2006 Well in the interest of making the car as stiction free as possible, it seems that it's very easy to avoid this additional side load on the strut, so why not avoid it? If you're building your own control arm, is there any advantage to building it this way vs the other? I would look at building the maximum stiffness and minimum friction if I were making a control arm. I think that would be a fine way to go. I guess I don't understand how you do this unless you start restricting movement with the LCA, like roller bearings instead of sphericals. And when you do that you run into issues with compliance as parts bend. This is sorta like the sway bar mod you did. You could use rollers but when the bar and frame rail bends they bind. So until I see a better way to do this I'll stick with what I know works. So if anyone can show me a better way then I'll be happy to scrap the current parts and build those. This car will never be done and this is why. Cary Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 30, 2006 Share Posted October 30, 2006 It seems from a design perspective that it would-be rather hard to eliminate or even reduce the already existent side loads presented on the strut shaft to a level that would reduce stiction to a level that makes enough difference to be noticeably effective. A strut by definition is “supposed†to take those sort of loads, and to design a suspension that doesn’t side load the shaft of the “shaft†itself, is another suspension design entirely, i.e. no longer Chapman or McPherson strut. To me, if the idea of keeping it a strut type suspension is the goal, wouldn’t it would make more sense to spend the time energy and money designing struts with reduced stiction such as installing linear bearings Reiger makes such pieces. There are very common on rallycross cars and used to be used on a number of rally cars. I don't know if ohlins, penske, or any of the other high end brands do this. Maybe JohnC can tell us. I think he ran Penske tripples on his car. At one point some of the high end touring cars were using hex shaft in an effort to have increased stiffness. I don't think anyone does this anymore because of the sealing issues. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 30, 2006 Share Posted October 30, 2006 Well in Ron's case, since he's not really talking about reinventing the wheel here (or are you Ron?), he could use the expandable link behind the diff to change toe, and rod ends and monoballs for the pivots. Nothing lost in terms of strength, nothing gained in terms of difficulty in adjusting toe. For a "relatively stock" suspension I think this is a pretty good way to go. If someone is going to change it to the point where NOTHING fits anymore and every part has to be made, then I'd start looking at other ways to get this done, and I certainly wouldn't rule out getting rid of the struts and going SLA. If you decide on going with SLA suspension, then that is fine too. I don't think you'll find too many people arguing that this is a bad move. Cary, I'm not saying that what you did is "bad". I just don't see the advantage of it vs what I did as far as the toe adjustment is concerned. I definitely see an advantage to lengthening the control arms and the strength of the frame where the control arm bolts up and the rest of it. But with the toe adjustment setup in particular it appears to me that comparing the two, the arm on your setup looks weaker. Maybe it's not weak enough to be an issue, you certainly know better than I do. I'm not saying mine is the only way either. I'm just saying that of the examples we're looking at, so far I prefer mine. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 30, 2006 Share Posted October 30, 2006 Jon, Per another long thead (stiction) about using spherical bearings on the inner joints (the outer joints were easy), I've gone ahead and sent the drawing to a local machinist to have these "housings" machined for 3/4" bearings that will replace the rubber bushings (similar in concept to the parts you recently purchased). Any progress on these parts and there application? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 30, 2006 Share Posted October 30, 2006 Yeah, just a little progress to report. Ron and Paul machined my tube ends. Just got them on Saturday. I'm going to have to get back out to the garage and get them installed. I've got some issues with that installation, but I'll post my potential problems on the other thread so as not to jack this one. Quote Link to comment Share on other sites More sharing options...
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