Administrators RTz Posted October 28, 2006 Administrators Share Posted October 28, 2006 I didn't include this in one of the other, closely related, threads becuase I felt this was enough of a tangent... don’t want to steal any thunder. The details are intentionally non-existant. The blue circles are the pivots. Pivot locations are in roughly stock locations, but likely raised to keep the RC’s in check. The strut assembly is, at this point, unmodified. The “bracktery†is meaningless. I only included it becuase I thought it made it a little easier to visualize. The goals: Less stiction... Elimination of all bushings. Replaced with ball joint’s, bearings, etc. Lighter weight... This will be tough, I think. I’m not hell bent on it, but weight is definitely a concern. Fully alignable... ...and preferably conveniently alignable. Some sacrifices in convenience may have to be made. As little structural modification to the car as practical. Thoughts on load paths, stress’s, pro’s, con’s, and any likes or dislikes are welcome. From above... Quote Link to comment Share on other sites More sharing options...
johnc Posted October 28, 2006 Share Posted October 28, 2006 The geometry is basically the same as stock except for a toe link at the rear. Make sure the toe link is strong and well mounted. Things get pretty hairy when one breaks. Make sure there are no toe changes in roll, acceleration, or braking. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 28, 2006 Share Posted October 28, 2006 I think there is more to be concerned with than just the strength of the toe link. By having pivots on BOTH ENDS, the toe adjuster will allow for the rear part of the control arm to move independently of the front part. The only thing stopping the strut assembly from tilting up in the back when viewed from the side is going to be the strut shaft itself, and side loading the shaft is not a good idea. All the stiction reduction is pointless if you introduce a bunch of side load on the strut itself. I think you could lessen the side load on the strut by attaching the toe adjuster to the rest of the control arm. Here's an idea of what I mean: The problem then becomes that the link for the toe adjuster is so long. That's an awfully big lever, and I think it might tear the arm apart sooner rather than later. What would be better would be something like this: This ties the front and rear parts of the control arm together, and then has a smaller turnbuckle with a pivot only on the outside end. But if you just want ease of adjustability, why not just use an adjustable end like AZC or MM has on their arms? Or the toe adjusting link like poor mans toe adjuster: http://forums.hybridz.org/showthread.php?t=89111 Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 28, 2006 Author Administrators Share Posted October 28, 2006 All the stiction reduction is pointless if you introduce a bunch of side load on the strut itself. How is this different than the side loads from cornering? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 28, 2006 Share Posted October 28, 2006 Well the struts are angled in, so that would at least reduce the side load while cornering. We know that the side loads in cornering are still VERY significant, and that's why strut tower bars and all that make such a huge difference. The load in this case would be perpenicular to the strut's fore/aft plane, so there isn't much you can do to offset that loading, other than securing the strut on both sides. So in this case what would be really dangerous would be a big dip in the road, or a "G out" as we mountain bikers refer to them. That would tend to really side load the strut, and I would think (but I don't know) that you could get a heck of a lot more verical g's out of a Z than you can lateral g's. I don't know if this makes any sense, but it's almost like mounting the strut in single shear with a bearing on the one mount. So all of the load goes through the strut shaft. In cornering, the load goes through the control arm to the frame, and only some of it goes through the shaft of the strut itself. That's my uneducated view anyway. I'm headed out the door, it's going to be interesting to see what's in here when I get back... Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 28, 2006 Administrators Share Posted October 28, 2006 I’m going out on a limb and try to explain something that I have very limited knowledge in, so if I’m way off base, please set me straight…. The stock rear control arm is quite strong in the loads it is subject to, but in regards to allowing the top of the strut to move for and aft to keep strut shaft stiction down, the lower control arm doesn’t really play any roll in limiting that. It isn’t very strong in that type loading, i.e. it will “twist” pretty easily considering the loads it is subject to. The strut shaft absorbs those loads, just like it does while cornering. With the top of strut unbolted from the car, you can force the strut to move fore and aft by hand causing the control arm to “twist”. Braking and acceleration loads are WAY more intense than the loads our bare hands can exert on the strut causing the control arm to twist. In short, the fore and aft stiction is already present in our Z cars and the design presented above wouldn’t be inducing much, if any more, stiction or strut loading fore and aft than what already exists. Now Double A-arm would eliminate stiction in the "shock" induced for cornering, acceleration, and braking loads….. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 28, 2006 Author Administrators Share Posted October 28, 2006 So in this case what would be really dangerous would be a big dip in the road, or a "G out" as we mountain bikers refer to them. Good point, I hadn't thought of that. My guess is that it wouldn't hurt the strut. I'd be more concerned about the stress on the A arm, particularly the forward mount and link. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 28, 2006 Author Administrators Share Posted October 28, 2006 I’m going out on a limb and try to explain something that I have very limited knowledge in, so if I’m way off base, please set me straight…. Dude, you're always OFF base Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 29, 2006 Share Posted October 29, 2006 With the top of strut unbolted from the car, you can force the strut to move fore and aft by hand causing the control arm to “twistâ€. Braking and acceleration loads are WAY more intense than the loads our bare hands can exert on the strut causing the control arm to twist. In short, the fore and aft stiction is already present in our Z cars and the design presented above wouldn’t be inducing much, if any more, stiction or strut loading fore and aft than what already exists. That's with soft bushings in place. When you remove all the rubber from the suspension then you have to start worrying about loads a lot differently, because there is no give anymore. With no bushings, pushing on the strut does nothing except side load the strut shaft. Now Double A-arm would eliminate stiction in the "shock" induced for cornering, acceleration, and braking loads….. Yes it would. The two of you guys could probably do up a SLA suspension setup fairly easily too... Quote Link to comment Share on other sites More sharing options...
heavy85 Posted October 29, 2006 Share Posted October 29, 2006 What BRAAP said - the LCA is not meant to take the F/A loads the strut is. Just like the strut is taking the side to side moment. I've never understood why everyone ties the toe link in solid to the A-arm as that technically makes it worthless for adjustability (without bending it) and if anything seems to weaken it since you are building in stress risers and preload. In my oppinion something like this is the better solution. http://album.hybridz.org/showphoto.php?photo=4667&cat=573&ppuser=9074 Thanks Cameron Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Heavy, Looks like I came dangerously close to copying Cary's car... I'm going to spend some time looking things over. Thanks for the link. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 29, 2006 Share Posted October 29, 2006 What BRAAP said - the LCA is not meant to take the F/A loads the strut is. A technicality here... The LCA is designed to take fore aft and lateral loads and actually does it quite well within the parameters of the original design. What causes stiction problems are: 1. Torque loads (acceleration and decelleration) which imparts a twisting load to the LCA/Strut combination with the hub as the center of rotation. 2. Spring deflection caused by vertical load path misalignment between the strut, the coil springs, and the spring perches. With a stock LCA properly modified and located with monoballs stiction from that part is basically eliminated until we exceed the capacity of the stock LCA's design and materials and its inner mounting structure. And with it properly located, torque loads can be reduced (but never eliminated) on the strut. EDIT: I wasn't clear - the main stiction component in the 240Z suspension is the shock shaft at the upper seal and the shock piston. Its fairly easy to practically eliminate stiction in LCA, very difficult and expensive to reduce stiction in the shock shaft. It took me $8,000 to come to a satisfactory solution to that problem. EDIT2: BTW... I'm aware that in an ideal situation the suspension shouldn't see any torque loads at all (the equal and opposite reaction thing between the ground the tire and diff) but halfshafts are never straight, wheels and tires are never perpendicular to the road and parallel to the chassis, etc. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 It took me $8,000 to come to a satisfactory solution to that problem. Is that something you can share with us? EDIT2: BTW... I'm aware that in an ideal situation the suspension shouldn't see any torque loads at all (the equal and opposite reaction thing between the ground the tire and diff) but halfshafts are never straight, wheels and tires are never perpendicular to the road and parallel to the chassis, etc. ...and, as far as I know, the only way to reduce it significantly under braking is inboard brakes. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 29, 2006 Share Posted October 29, 2006 What BRAAP said - the LCA is not meant to take the F/A loads the strut is. Just like the strut is taking the side to side moment. I've never understood why everyone ties the toe link in solid to the A-arm as that technically makes it worthless for adjustability (without bending it) and if anything seems to weaken it since you are building in stress risers and preload. In my oppinion something like this is the better solution. Take a closer look. That is a CLEVIS on the inboard pivot of the adjuster, not a rod end. So that looks a lot like my first drawing. [ proud of myself ] No bending going on with the clevis, because you just loosen the bolt, adjust the toe, then cinch the bolt down again and now the toe adjusting link DOES provide strength to the the control arm, and does take some of the F/A loading... 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, Honestly, I am not able to see the clevis providing the kind of strength that you're talking about. I see it as pretty weak in bending. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted October 29, 2006 Share Posted October 29, 2006 A technicality here... I realize that just wasn't clear - the LCA as you say is meant to take F/A loads but it is not efficient at taking moments about the spindle pin. Take a closer look. That is a CLEVIS on the inboard pivot of the adjuster, not a rod end. So that looks a lot like my first drawing. [ proud of myself ] No bending going on with the clevis, because you just loosen the bolt, adjust the toe, then cinch the bolt down again and now the toe adjusting link DOES provide strength to the the control arm, and does take some of the F/A loading... I'm still not convinced the toe link will realy take any moment loads about the spindle pin. Consider if you remove the spindle pin and pull up and down on the toe link you could deflect it faily easily with low loads. Now consider that any moment load is imediately felt by the strut - in other words I think the strut would have to deflect a lot before the toe link really started to take much load. I'm guessing it's more of a manufacturability issue to use a clevis on the inboard end but Cary would have to say for sure his intentions. Cameron Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 29, 2006 Share Posted October 29, 2006 Honestly, I am not able to see the clevis providing the kind of strength that you're talking about. I see it as pretty weak in bending. You might be right, the clevis isn't my first choice here, but even so, you'd use one in a TC rod where the entire force of the braking is trying to snap the thing in half? Cary and I think it was jt1 have talked about BENDING the J Bar that was attached to the clevis. Haven't yet heard anyone talk about breaking a clevis. I think they're pretty strong. Maybe not as strong as a full control arm. But again, I think the weak point is the span and not the rod end or the clevis. Cary used an aluminum turnbuckle. That's the part that I'd be worried about. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted October 29, 2006 Author Administrators Share Posted October 29, 2006 Ouch! that's gonna leave a mark 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. 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, In looking at it again, I didn't say that well to begin with. I was trying to reference the entire toe link, including the clevis, as a flexible arm vertically, with only the clevis to stop it. Quote Link to comment Share on other sites More sharing options...
JMortensen 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. Badly worded on my part. I think it was Cary and jt1 that bent the J bar. I think I'm in the process of building a car serious enough... I agree with you that the situation in back isn't the same. My fear is that this situation in the back is WORSE than the TC rod situation up front. Can't someone with some math skill (this precludes me) figure out what the actual loading would be? The length of my sectioned strut from the gland nut to the bottom of the cast iron housing is 15.5", add about 3" from the bottom of the strut to the rod end. So say 18.5" tall. Then the strut itself has ~5.5" length from front to back and we know this is 90 degrees from the strut tube. Since the strut is mounted entirely behind the attachment point in back, then you should have the full 5.5" of lever from where the pivot is at the front rod end to the end of the strut tube the way I see it. So lets say you can do 3 g's in bump (I think that might be low, but let's just use it as an example). If you have a 2000 lb Z with equal corner weights, that is going to be 500 lbs x 3 g's or 1500 lbs on the end of that 5.5" lever. What kind of pressure to the rear is that going to get you at the top of the strut? Anyone smart enough to figure that out? Quote Link to comment Share on other sites More sharing options...
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