w116 Roll Center Correction (Page 2 of 2)

In the words of so many young women today. OMG!!!!

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.

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.

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.

Same answer as for the rear bar, measure it and hit the JY.

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.

Thanks for the great info Mackwagon. I'll be in the JY today and they have a stock w116 I can check out with my calipers and tape measure.

For stiffer springs look to vans and SUVs, we found that Chevy Astro van springs at around 800 lbs fit a 3rd gen camaro and 65 Impala rear springs increased the rear by around 100 lbs.
Jeep cherokee fit a RWD Celica etc

If you know what you have got then try this handy dandy Moog look up table to find something with the same diameter but higher rate, that gives you the drop you need, remember cutting will increase the rate further.
http://classiccarsprings.com/coil-sprin … tions.html
Then go buy the new springs or junkyard, most new springs run at about $50 a piece on Rockauto/amazon etc.

These guys made a noticeable difference in our E30.

Single shear roll center correctors freak me out. I'm sure plenty of people use them without issue. If something can't take rally abuse I don't want it in a car I'm racing.

It's mentioned above to put blocks to improve lower control arm angle. Realize the control arm angle doesn't matter, it's the center of the ball joint to the center of the control arm bushing angle that matters.

Lower control arm angle in any correct suspension talk/book is referring to pivot point to pivot point of the control arm. Draw it out, blocks change the physical control arm angle but gain you nothing because the pivot point doesn't change. If the ball joint bolts to the steering knuckle/ wheel bearing housing and the block moves the pivot down from the wheel centerline then yes. Most ball joints bolt to control arms and blocks do nothing in this case.

The single shear roll correctors work but add weakness. Not something I like trading for.