In the words of so many young women today. OMG!!!!
FPRbuzz wrote:Do you know how to use MsExcel or similar spreadsheet programs?
Yes
OK, starting with the unlikely, but do able. Like "the Shaolin" stated. Order a copy of How to make your car handle. Then build a spreadsheet with the formulas from the book and plug in your suspension dimensions and see what results you get. The upside to this is you can then plug in different spring rates or/and different roll bars to see what the effect on your "handling" should be like. But build it for the stock suspension, then make a copy for your current modified suspension, and then make a copy for the optimized suspension.
OR we'll make some assumptions and you can just try this stuff out. See next answer.
FPRbuzz wrote:Can you tell me what spring rates you have in the front and rear?
Sadly no. They are stock springs that we cut coils on.
OK at least make a spreadsheet with spring parameters in columns (cell b5 is wire diameter, B6 is coil Outer Diameter, B7 is free coils, B8 is measured unloaded lenght). Use the spring formula that Chesero links to in the last response. Calculate your stock front and rear in Column B and C. Calculate the cut down springs in columns E and F, make a copy for new JY springs in columns H and I and maybe a couple more.
Measure your wire diameter and outer coil diameter. The nominal coil diameter is the outer DIA - 2 x 1/2 the wire DIA or more simple outer coil DIA - 1 wire DIA.
for free coils, if your ends are flattened look closely at when the coils start to be free, usually about 3/4 of a coil from the starting point. If you cut the coils its all in play for the cut end, so count free coils right to the end
You need to look at the lower control arms pivot to spring center, vs pivot to ball joint length. The effective wheel spring rate is a function of the ratio of the control arm. UNLESS you are using a coil over. If the spring is over the strut, its 1 to 1.
Tell us what those rates you calculate are. I'm guessing you'll have rates in the 150-200 #/in range. I'm also guessing you'll want rates in the 400-600#/in range for a 3500# car. Maybe higher if the LCA ratio is low.
The Valiant (my Car) seen in this photo is ~2600-2700#. 400#/in dodge van springs on the rear with a Datsun 510 7/8" roll bar. A combination of stock 110#/in torsion bars and some ~300#/in coil overs on the fronts, but de-rated by the LCA ratio with a 1.125" Mustang roll bar. Notice the VW has more roll
http://www.murileemartin.com/UG/LAF14/0 … _8440.html
http://www.murileemartin.com/UG/LAF14/1 … _9044.html
Here notice the BMW an MR2 have less roll than the valiant, but the VW has more. Also look at the Left front wheel of the Valiant. its just about 1-0 deg camber under moderate cornering, an 0-1 (out) under hard cornering. Its about 4 deg in at the top with the car level. (see more below)
OK, what to do.
Bigger rate up front . 2 wheel up front tricycle cars corner OK, 2 wheel to the rear tricycle cars corner like shit, RIGHT?
Option 1: Hit the JY with your computer and measuring device and find some new springs that when cut will give you about 500#/in wheel rate, maybe 600 or 700. Your looking for the same OD as your stock spring, but a bigger wire DIA or less coils in the same length If you get a tall 500#/in, you can cut it down after 1 race and try the 600#/in version.
Option 2. I'm going to guess that finding a big enough spring to get to 500-700#/in rate is going to be difficult (6000# cadillacs?).
So double spring it. Hit the JY and look for springs that have an OD that fits INSIDE your current springs. So (example) you have a 5" OD with a .540" wire DIA, your inner DIA is 5-2x0.54 = 3.92". Now this gets complicated in calculating the right length of each spring vs the rate. Basically what you want is the UNLOADED length to be the same. Then you can calculate the rate of each and get a combined rate. You could get a little trickier and make it progressive, but having one spring just a little longer than the other, but I' vote against that, its even more complicated.
FPRbuzz wrote:Do you have a rear sway bar?
Yes. It's a twig, ~12mm.
OK some people say no rear bar or a small rear bar. I'm using a small datsun bar 7/8" or ~22mm on the 2700# Valiant and in the first picture, above, you can see the right rear tire is almost off the ground. need more something somewhere (probably more front spring). Your 12mm rear bar is ~ 1/2 the size on a heavier car, so its probably undersized. See if a front bar will fit the mounting locations at all. Or measure the end location and hit the JY to see if you can find a similar shaped bigger bar. what every you do make the rear smaller than the front (smaller DIA with the same length arms).
BUT the most important thing IMO is Spring rate. Fix that first then figure out the roll bars.
FPRbuzz wrote:Stock front bar?
Yes. Stock bar with good condition bushings and endlinks.
Same answer as for the rear bar, measure it and hit the JY.
FPRbuzz wrote:3500# is the current racing weight?
3500# with a driver and 1/2 tank of fuel
FPRbuzz wrote:How is the camber on the front wheels? Or what Static (car on the ground) camber do you have (even eye ball it). 0 degrees? +3 (top out), -2 (top In)???
Static camber right at 0° static
OK not nearly enough Camber. With the Lower Control Arms horizontal (draw a picture), when the suspension compresses, the arm moves up the curve ( and the camber goes positive (top out), which rolls the tire onto its outer edge and the front end slides (pushes). I'll bet your tires have plenty of tread on the inner edge and cord showing on the outer edge at the end of the race Valiant has about 3-5 degrees in at the top. front tire wear is even and very light. We get ~3 races out of set of tires.
Options: move the upper strut mounting point inward, or move the lower ball joint out.
HOW: get rid of the upper isolator and install a flat steel 1/4"plate. drill a couple holes for the upper strut inward of center. Maybe every other one on the Center line and the others to the rear by 1 DIA. or something like that. Or just figure out via some math where you thing you need to drill. I'll guess again and say that the strut rod needs to be at the inner end of the current upper mount opening or slightly further inward.
OR: cut the lower arm and weld in either a extra section, or cut the inner end off and weld in a threaded rod with a threaded Heim joint end to make the LCA longer. Use washers to space the Heim joint fore and aft in the inner mount. Put on a locking nut. This is adjustable (very cool)
Also if you put blocks in between the LCA and the ball joint the LCA gets more angle downward, starting out lower on the radius curve ( , and so when your front end compresses you get back to mid point an only have 0 camber (see the Valiant photo again).
Report back.
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