74_5.0L_Z

Thanks for the responses. Jon you are correct, I am neglecting the tire contribution to roll. Also, I lowered my tire pressures for this event. I have previously been running 40 psi front and 36 rear (cold), for this event I lowered the front to 32 and the rear to 28. I am just shooting in the dark until I get a tire pyrometer. That will be my next purchase. Cary, I have been wanting to try droop limiters. My next event is in 2 weeks in Gainesville, Fl (05/18/08). I hope to have droop limiters on the front by that time. From my picture, it appears to me that the inside tires are fully drooped (limited by the struts) and that the outside tires are on the Koni bump rubbers.

Saturday, I finally got the car aligned for the first time since redoing my suspension. Here are the alignment settings that I used: Front: 0 toe, -2.5 degrees camber, and 5.6 degrees caster. Rear: 0.10 degrees toe in, -2.1 degrees camber. Sunday, I ran an autocross and the car did extremely well considering that I have some seriously dead Hoosier A3S04 tires. At the limit, the car had just a little understeer, and the rear traction was much improved from the last couple of events. I attribute this to using less rear camber and less toe in at the rear. There was a photographer present, so I asked him to get some pictures of the car in various parts of the track. The following picture surprized the heck out of me. The picture was taken at the end of a fast sweeper with a decreasing radius exit. The body roll in the picture is about 3 degrees. This is more roll than I expected the car to achieve with the tires and suspension that are in place (Hoosier 245/45/16, 450 lb/in front springs and 425 lb/in rear springs). The weight transfer worksheet predicts 1.6 degrees of roll per gee of lateral acceleration (for a steady state 1 gee turn). I guess I overlooked the additional roll that will occur in transient manuevers. Also from the pictures, it looks as if the rear tires have sufficient camber to compensate for body roll, and it looks like the front tires could use a little more negative camber. Unfortunately, in order to get more negative camber on the front I have to either lengthen the lower control arms or give up a little bit of caster. I will probably make some new lower control arms (and outer tie rods) to widen the front track, and allow me to run more static negative camber. Before I do make new control arms, I plan to do the following to add to this thread: Measure front camber gain. Measure front bump/roll steer.

Like johnc, I am using Outlaw 2800 calipers on all four corners. I've been quite happy with them.

Thanks Jon, Were you using the bias ply or radials? Bias Ply P/N________Size_______App______TW_____Dia______Circ_____ Rim Width 43361__22.5 x 9.5-15___FA______9.2"_____22.9"_____72.0"_____10" Radial P/N________Size_______App______TW_____Dia______Circ_____ Rim Width 43570__23 x 9.5R-15____FA______9.4"____22.9"_____72.0"_____10" These would both be good options for my car. Regardless of which of these tires that I select, I am going to need some different wheels.

Cary, Thanks for the reply. All of those cars look like some serious hardware. I love the big rear quarter panels. Makes me wish that I had flared mine a bit further (but alas). Hoosier lists several FA tires on their web site. These tires range in size from 22.0 x 9.0-13 to 23.5 x 11.0-15 in Bias Ply slick and 23 x 9.5R-13 to 23.5 x 13.0R-15 in radial slicks. The big tires for both are supposed to be mounted on 14" wide wheels:shock:. Are you guys using the Bias ply or radial tires? Because of my brakes, I cannot use the 13" at all, and the available FA 15" sizes are incompatable with my bodywork. With the right selection of backspace, I could fit these Hooiser Bias Ply tires on all four corners of my car. P/N________Size_______App________TW_____Dia______Circ_____ Rim Width 43470__22.0 x 10.0-16__GT2_______ 9.7"___ 22.9"____72.0"_____10" Other options are to use the R6 DOT radial tires from Hoosier. The following could be made to work on my car: P/N________Size________TW_____Dia______Circ_____ Rim Width 46535___P275/35ZR15___10.1"___ 23.0"___ 72.2"______ 9.5" 46630___P275/45ZR16___10.3"___ 25.6"___ 80.5"______ 9.0" 46730___P275/40ZR17___10.3"___ 25.5"___ 80.1"______ 9.5" I have been trying to decide whether to stick with a DOT radial or to try a bias ply slick. Which lasts longer? I am tired of tires that "go away" after only a few events. I love the pictures as a means of troubleshooting the car. I will try and get someone to start getting some pictures of my car at work. You mentioned that one of the crew is using droop limiters. Is he using them on the front and back, or just on the front? I have been toying with droop limiting my front suspension.

Me too. No rear bar.

Jon, You are probably right. I'm just looking for a good starting point.

In my previous post, I stated that my car would roll 1.6 degrees per G and that I had set the static camber to -1.3 degrees. The static setting of -1.3 degrees would give me -1.89 degrees on the outside tire in a 1 G turn. I was happy with myself because I had stood the tire up a little bit more vertical and convinced myself that I would have enough camber at max lateral acceleration. Then Cary (Tube80Z) had to go and inject a little reality: "I should be generating 1.3 to 1.5 gs of lateral acceleration." At 1.5 G my car should roll 2.76 degrees, the outside tires should rise (relative to the body) 1.2", and the inside tire should droop 1.2" from their static ride position. With -1.3 degrees statics camber, I will have about -2.2 degrees of camber in a 1.5 G turn while the body will roll 2.76 degrees. The tires will go 0.5 degrees positive in camber. I want at least enough camber to offset the body roll. I'm looking for the least amount of static camber to improve my forward traction, but I want enough camber to prevent the tire from going positive due to body roll. So, I generated some camber curves for several positions of my camber plates. For each of these positions, the static ride height was held constant (5.75" at rear of the rocker panel, or 7.125" at the center of the LCA inner pivot). On this graph 0 on the X axis represents my static ride height. Displacements to the right represent bump of the tire and while displacements to the left represent droop. Each of the curves represent a different setting of the camber plate. The bottom curve is what I have settled on (for now). I have set the rear tires to have -1.88 of static camber. This will give -2.8 degrees of camber on the ouside wheel and 0.88 degrees on the inside wheel in a 1.5 G turn. If you analyze the graph, you can see that there are two things that affect your camber. First, If you hold your ride height constant, you can increase/ decrease camber by adjusting the camber plate. Second, with the camber plate adjustment held constant, you can increase/ decrease camber by lowering/raising the ride height of the car. If you look at the curves, raising the ride height 1" makes the camber become ~.74 degrees more positive. So as Terry noted: the Ground Control camber plates will be set at or near there maximum outboard position on a severly lowered car. BTW: Cary what wheels / tires are on that car? I'm trying to decide which tires are going on mine next.

In going through all of this process, I have installed 425 lb/in rear springs, 450 lb/in front springs, replaced my front 1" sway bar with a modified stock (18 mm) sway bar, and lowered the heck out of my car. The car is about 1.5 " lower than when I started this process and about 3.5" lower than stock with 245/45/16 tires. The car is much better in transitions than it was, but I have been having trouble putting down the power since going to the higher spring rates. I have not aligned of or corner balanced the car since starting this process. Just looking at the car though, it was obvious that the rear tires had acquired a bunch of negative camber. At the old ride height with the 250 lb/in rear springs, I ran -2.0 degrees of rear camber. At the new ride height, I found that I had -3.7 degrees of rear camber. Perhaps this accounts for some of my lost rear forward traction. So, I decided to try and set my rear camber to a more reasonable number. That begs the question: What is a good rear camber setting for my new suspension setup that will optimize forward traction without letting the camber go positive with body roll? To answer that question, I needed to know two things: First, how much will my suspension compress in roll? Second, how much camber gain will my rear suspension give me per inch of wheel travel? To answer the first question, I did the suspension analysis as outlined in RCVD and as implemented in the weight transfer worksheet. The weight transfer worksheet predicts 1.6 degrees of roll per G of lateral acceleration. To answer the second question, I spent today measuring camber curves for various positions of my rear camber plates. What I ended up with was setting the plates as far towards positive camber as the slots would allow. This yielded -1.3 degrees of camber at static ride height. The camber gain at this position is -0.74 degree/ inch in the range centered around my static ride height (The camber curve is not really linear, but can be approximated as linear over small ranges). If we assume that the suspension rolls about the center (big assumption), that amount of roll corresponds to approximately 0.8" of bump on the outside wheels and 0.8" of rebound on the inside wheels. If we also assume that we want the tire vertical at 1 G lateral acceleration, then we choose a static camber that will yield -1.6 degrees at 0.8" of bump. For my case, the most positive that I was able to set my camber was -1.3 degrees at static ride height. At 0.8" of bump (1.6 degrees of roll), the camber should be -1.3 deg - (0.74 deg/in x 0.8 in) = -1.89 degrees. This value is more than the 1.6 degrees of body roll, so I should have a little camber more than the minimum required to keep the outside tire from going positive. I'm sure that I have oversimplified some of this, but I am quite sure that the car will be a bit happier than it was with -3.7 degrees of static rear camber.

I've been using black aluminum pop rivets from these guys: http://www.colemanracing.com/catalog/product_info.php?products_id=3181 They are $21.59 for 100 rivets. They look exactly like the factory plastic rivets. The down side is that removing them requires that they be drilled out.

I had a ball joint that was worn, so I cut it apart while I was trying to locate my roll centers. I found that the center of the ball is approximately located along the upper surface of the webbing for the four bolt flange where it meets the spherical housing of the ball joint (right where the webbing blends into the housing). This will get you within ~1/16". To be a little more clear, I mean the most outboard point where the webbing meets the housing.

The center to center length for the front control arms (using a tape measure) is 11.25". The rear control arms are 14.5 center to center. Be careful about the factory frame drawings. The 240Z and 260Z factory manuals had some errors. I believe the errors were corrected in the 280Z drawing.

Jon, Go to the following link: http://www.fromsteve.net/carstuff/suspension/SuspensionCalc.htm After the page opens, select the Sway Bar Rate Calculator tab at the bottom of the page. On that page is a figure of a sway bar with dimensions A, B, C, and D. Would you measure those dimensions for me on your sway bar and post them here? Ignore the extra bend in the sway bar. The extra bend in the Z sway bar provides clearance for the L6 oil pump and really only has a small affect on the stiffness. Dan

I experimented with my front sway bar today. The purpose of the experiment was to quantify effective spring rate of the sway bar at the outside wheel. Here are the specifics of my front sway bar: Modified suspension techniques 25 mm front sway bar: The lever arms have been shortened and fitted with rod ends. The measured dimension of the bar are as follows: A = 7" ---------Length of lever arm measured perpendicular to B B = 30.5 " --------Length of bar in torsion C = 7.75" -------Length of lever arm (along arm) D = 1.005"-------Diameter of sway bar Sway bar installation ratio 0.58 Fred Puhn gives the following formula for the stiffness of a sway bar on page 150 of his book, "How to make your car handle." K = (500,000 x D^4) / (0.4244 x A^2 x B + 0.2264 x C ^3) For the dimensions of my bar, the theoretical stiffness given by Puhn's formula would be as follows: K = (500,000 x 1.005" ^4) / (0.4244 x 7" ^2 x 30.5" + 0.2264 x 7.75" ^3) = 689.6 lbf / in This measurement gives the stiffness of the sway bar for one inch of deflection at one sway bar end. To find the stiffness for one inch of deflection at the wheel, you multiply the stiffness by the square of the sway bar installation ratio. So for my car, the theoretical sway bar stiffness for one wheel rising 1 inch with the other wheel locked in place should be 698.6 lbf/in x 0.58^2 *1 inch= 231 lbf Formulas are great, but their results need to be verified, so here is what I did: Removed both front springs. Replaced the drivers side spring by a 7" x 2.5" x 0.125 wall aluminum tube. Reconnected both struts (one with no spring and one with the aluminum tube to lock that side at ride height). Disconnected the sway bar. Placed a bathroom scale (analog type) under the passenger side front hub with a scissor jack, and raised the hub (with out spring or sway bar) to ride height. Record weight of hub, and scissor jack. (67 lbs) Connected sway bar. Raise hub using scissor jack until hub rises 1 " above starting position. Record weight of hub + scissor jack + force of sway bar. (275 lbs) Subtract initial measurement (hub + jack) from final measurement (hub + jack + force of sway bar) to get the force at the hub caused by 1 " of wheel motion. Here are the results: 275 lbs (hub + jack + force of sway bar) 67 lbs (hub + jack ) ______ 208 lbs (measured sway bar force at hub for a single wheel deflection of 1 ") This is slightly less than the force predicted by Puhn's formula. The error is (231 - 208)/231 = 10.3 %. In all fairness to Mr. Puhn, much of that error can be accounted for by the inaccuracies of my own measurements.

I was poking fun at the picture. I was not criticizing. I'm quite sure that my situation looked just as comical to innocent bystanders.

I'm sorry, but that looks like it should be included as a workplace safety message. I sure my job would have been included on the same page.

After I finished the tube front end on mine, I needed to prep and paint the bottom of the car (from the rear crossmember forward). The front suspension was removed and there was no drivetrain or interior. The rear suspension was installed, so I grabbed the two front frame rails and rolled the car out of the garage like a big wheel barrow. Once in the driveway, I blocked the rear tires and stood the car up until the rear valance was almost on the ground. I secured it in this position with a rope up to a tree limb above. I was then easily able to scrape, clean and paint the underside of the car.

I switched to Hypercoil springs because I have heard that they have less variation in spring rate than some of the others. But yes, if I ever get truly serious, I would need to measure the rate and free length of every spring (and recheck periodically). In the meantime, I'll get as close as I can using off the shelf spring rates and movement of weight. The deeper you look, the deeper it gets.

I will try to measure the bar. A simple experiment is worth a thousand calculations as long as all the variable are covered. How long are your lever arms on your sway bar? Were your bearings located near the stock location near the bend in the bar? How flexible is the workbench that it was bolted to? Were you measuring the deflection at a point equal to the end of the lever arm, or were you measuring the deflection at the end of a longer lever?

I dug out my statics text and went through the torsion calculations and if I assume infinitely stiff lever arms, I get pretty close to what the WTW calculates for a 1" sway bar. The WTW comes up with 659 lb/ in (That's one inch on each side), and I came up with 592 lb/in (Again one inch on each side). I do plan to measure the rate, but I am pretty darn sure that it will measure greater than 120 lb/in. Is it possible that you annealed your bar by welding on it? I have seen suggestions that sway bars that have been welded need to be heat treated.

I already had my 1" sway bar in place and haven't had time to measure it's rate or install the sway bar that my calculations say should work (stock 0.71" sway bay modified for rod ends and 7.5" lever arms). I ran the car with the 450 lb/in rear and 425 lb/in front with the 1" sway bar. The weight transfer worksheet gave me a magic number of 9.4% which predicts understeer (which it did). With the new sway bar and swapping the springs front to rear, the weight transfer worksheet gives me a magic number of 3.2% which is much closer to neutral. My calculations for the sway bar rate agree pretty closely with what the weight transfer worksheet predicts. John, I plan not to miss any more seat time regardless of the springs that I have installed. My next event is one month from now. By then, I will have the new sway bar set-up in place and hopefully the new springs. I'll wait till I get the new springs in place before I get it balanced. Oh, my weights are with me in the car and a full load of fuel.

I ran an autocross yesterday with my new set-up (sort of). I had all of the new springs and struts in place, but I haven't had the opportunity to re-corner balance the car or get it aligned. Additionally, my front sway bar is much too large for the springs that I have chosen (I was pushing a bit). Nevertheless, the car did pretty well. I took first in E-mod against 4 other cars in my class. I will say that the new set-up will take some getting used to. The car reacts much quicker with a 2.5 Hz suspension frequency than with a 1.8 Hz frequency. I think that I will like it as I get accustomed. As I was inspecting the car today, however, a strange and troubling thought occurred to me: These cars are not symmetric left to right. The left side is heavier than the right side. Yet, the spring that I put in the left front is the same rate as the spring that I put in the right front. The left front sprung weight is 586.6 lbs and the right front sprung weight is 543.6 lbs. The resulting frequencies for the left front and right front are 2.28 and 2.37 respectively. The resulting frequencies for the left rear and right rear are 2.20 and 2.28 respectively. So, what does all this mean? It means that in order to have the suspension frequencies match left to right, the car needs four different rate springs. For mine, I would use the existing 450 lb/in spring on the left front, and use a 410 lb/in right front spring. On the rear, I would use the 425 lb/in spring on the left and need a 390 lb/in spring on the right rear. By doing all of this, the car should sit level when corner balanced and transfer weight forward and backward equally between the left and right tires during acceleration/braking. Please someone tell me that I am full of crap. Otherwise, I will be ordering two more springs.