How 'bout this for a race setup?

[gramercyjam]

Pancho,

The 300# springs on my car are the spring rate (Eibach ERS, 7" springs in the front, 8" springs in the back). I run a 1" sway bar in the front that mounts like a stock sway bar so the dimensions are similar and a 7/8" in the back that bolts to floor just behind the seats in the area that slopes up. I don't know the brand, I got the bars second hand from Dennis Thoney's GT car, but they are pretty stout solid forged material. All bushings on my car are the poly type. I run my 16" wheels and tires extremely close to the struts (you can slip a piece of paper between the wheel and strut) and that affects wheel rates somewhat, giving me a little more stiffness than the typical race tire'd car. The stance feels like it handles pretty level and flat in all situations.

Here's a pic of the car in an extreme braking/cornering situation at the end of a long straight with me braking way too late .....

[panchovisa]

Alright guys, smoke-em if ya got em! (tires that is)

Ya never know how late you can brake until you wait to long.

I used to know how to figure the wheel rate, but since AARP started sending me membership forms I've forgotten.

Springs are rated according to how much weight is required to compress 1 inch of travel (constant rate springs). You must apply 300 lbs to compress your 300# spring 1 inch. A sway bar is basically a torsion bar (spring) without a fixed anchor. One end moves up as the other end moves down while the "spring" portion of bar tries to resist.

Seems to me that the easiest way to measure the spring rate of front sway bar would be to jack car up level, place jackstands at the back, place one front wheel on blocks, place jack or jackstand under frame at other front, disconnect T-C rod, drop link, and balljoint from A-arm. Let arm swing out of way (tie strut to wall in garage so it doesn't get in the way. Add a plate to bottom of drop link (simulates A-arm, but not anchored) where you can start hanging weights. Measure height of end of sway bar then add weight until you get 1" of deflection. The number of pounds needed to delect one end of bar would either be the bar rate or twice the bar rate (unsure about that point, Help from an engineer would be appreciated). This method would take into account all the variables encountered in actual installation (frame stiffness, style of drop links, play in bar mount, etc.).

The rear would be more difficult to get arm out of the way without pulling pivot pin (not fun), but could be done by dropping arm at inner pivot.

Your picture shows body roll so the rate of the bar is adding to outside wheel rate.

[panchovisa]

Oh, I also forgot that the effective spring rate of the bar would be increased by a percentage relating to it being working on a shorter lever than the strut spring (sway bar mounts closer to inner A-arm pivot than the ball-joint), but would be the same from Z to Z.

[gramercyjam]

Hey! I'm an engineer, but all this engineering stuff makes my brain hurt. I don't think I have anything heavy enough to hang to deflect the bar by 1" (well maybe if I could hang the suburban from it), but I think that measurement would be the rate.

[panchovisa]

Just borrow weights from the neighbor kids gym! If it take more than 300# who gives a $hit what rate springs you use as they are less important than the transient rate of the bar:)

[260DET]

Here are some Z anti roll bar rates that were posted here or at HybridZ some time ago. Using the stock bar setup.

Front: 22mm - 268lb/inch, 23 - 321.

Rear: 20 - 86, 21 - 105, 22.5 - 139

One reason why I prefer heavier springs to anything larger than a 22mm front bar.

[panchovisa]

260DET, thanks for the numbers. I feel much better about my 260# front and

240# rears now (nice numbers hey!). I'm using a 28.6mm adjustable front (five or six positions) and 22.2mm rear (with four positions and much shorter "arm" than stock).

So I'm just guessing that my front bar should be adjustable from 400# to 600# and my rear from 150# to 250#.

The much lower rate on the rear may be the reason why some racers use stiffer springs in the back.

[sopwith21]

Okay, guys. Many thanks for the thoughts offered so far. I wish I had talked to you all earlier, but I didn't and that's life. Here's the parts I have now... they're paid for and its not negotiable, so the trick now is to do the best I have with what I've got. My next race is at the end of the month and I'm in the points battle.

Springs: 350 fr/250 rear

ProShock coilover kits (4)

Tokicko 5 way adjustable struts (4)

Sway bars fr and rear, don't know sizes yet. Stock with no pre-load adjustments.

Hoosier R55 slicks

8 of the 11 corners at the next track are left handers... so... if I end up with a push (the parts are going on this week), here are my rather limited options:

- increase rebound on LR strut to wedge car out of corners and increase fr grip

- take off two rounds of coilover on LR and RF tires to wedge car and increase fr grip

- put a bigger tire on the RF for same effect

- swap springs fr to back and hope for the best (but I don't know if we'll have time and ability to do this at the track, so I can't count on that)

In the unlikely event that we end up with an oversteer, we can:

- unhook the rear sway bar for more bite in the rear

- do the opposite from above on tire stagger and/or coilover adjustments to tighten car

YES! I realize that some of this is a band-aid, but as I mentioned, this is what I have to work with. Our money and time are nearly gone and the challenge now is to do the best we can with what we have.

The suggestions you guys post are helping more than you know and its appreciated. We may not have the perfect parts, but we've got to work with what we have and get close... and I think we should be able to at least do that much. Thanks again to all.

[sopwith21]

BTW, air pressure adjustments on a tire this hard seem to have only a the most minor effect, so I left that possibility out. When you're tuning a car from absolute zero, your first adjustments have to be major to get your car in the general ball park.

What fr/rear weight ratio is best when we scale the car? Now that we have coilovers we should be able to make some adjustment there.

[panchovisa]

Sopwith, I don't know what you mean by taking two rounds of coilover off RF and LR. That will only affect the ride height (lower) at those corners and increase weight at opposite corners and has no effect on wheel rate.

I hate the idea of jacking a road race car out of whack.

Try something less drastic like lower LF air pressure (slight stagger), more camber on RF (or both), more preload on RF of sway bar (stiffer wheel rate on left turns), more toe in, or a little more castor (shim T-C rod). Also try not to over cook your turn entry, and use throttle to balance out understeer (blip-blip).

I'd find a parking lot and run a skid pad circle trying some adjustments prior to track time.

Just my 2 cents.

[sopwith21]

Sopwith, I don't know what you mean by taking two rounds of coilover off RF and LR. That will only affect the ride height (lower) at those corners and increase weight at opposite corners

Exactly. Its an old circle track trick called "wedge." That deliberate stacking of crossweight helps turn the car in (for instance) left hand corners. Of course, it hurts you in right handers, but if the car is pushing and you're getting creamed anyway, you might as well try to get better in 8 of the 11 corners on our road course.

I hate the idea of jacking a road race car out of whack.

Me too. But if the car is awful and I have no other options, we can do it temporarily to try and pick up some time. I'm just trying to plan for a worst case scenario.

Try something less drastic like lower LF air pressure (slight stagger), more camber on RF (or both), more preload on RF of sway bar (stiffer wheel rate on left turns), more toe in, or a little more castor (shim T-C rod).

Good idea. I've tried using air pressure adjustments to stop understeer, but I've not used it yet to adjust stagger or crossweight. Great thought. I wonder how much these tires will respond to staggering by air pressure?

[260DET]

With 250f/350r springs you could try doing without the rear anti sway bar, remove or loosen one link right off if you don't have time to take the whole bar off. With both stock bars in place though the car should oversteer if anything.

Or, if the springs are interchangeable swap them front to rear. But I'd play with the rear bar as above first. Don't want to know about the speedway tweeks

If it still wants to understeer no matter what you do with setup, try some light left foot braking through the problem corners, keeping the power on though and assuming that the brakes can take the extra work.

And let us know how it all goes, fascinating stuff.