[railing68]

I am looking for a coil spring rate recommendation:

Car is street driven but used a lot for auto-x and pending track days!

I am looking to help eliminate push/plow and was under the impression that a stiffer coil would only increase understeer.

Under fairily tight turning ie. pivot cones and slalom I am experiencing scrub/push!

The car handles very well aside from issue stated above, which is becoming more of an issue as times improve etc.

here are some specs

Coils are HO 465lb 7 coils
GW arms w/Gmod-delalums in UCA and LCA-
Solid body mounts
1.25 solid sway bar
Bilsteins
Hotchkis leafs w-Delalums pending install
175-180lb

I was previously told with a solid big bar that spring rate should be lower around (500lb) now GW states should be 700-800lb.

auto-x alignment is -1.7*camber, 6* caster.

Tires are NItto 0-1s 245-45-17 all for corners.

Looking for a little guidance.
Thanks, SS.

[HarleyD67]

I'm sure Dave will pop in on this one.
But mean time check out his site for some good info. www.pozziracing.com/first_gen_suspension
Any rear sway bar or other traction devices?

[davidpozzi]

I'd install the rear springs ASAP.
I would keep the rubber bushings in the front spring eyes and use either rubber or polly in the rear spring eyes. The top shackles can be Del-A-Lum. This allows the leaf to twist in the bushings when you corner preventing bind and ovesteer problems.

If body lean is 3 degrees or more under hard cornering after the leaf install, then I'd go to a 600 to 700 front coil and add a rear anti-roll bar. I think you are going to wind up with the stiffer front coils in the end. But a lot depends on how much traction you have and how hard you drive it, also the traction at the site you run.

David

[railing68]

The hotchkis leafs have been installed with urethane bushings for quite a while. guess I should have been more clear.

Removed the rear bar due rotation on the axle housing-no matter how tight the mounts were and traction issues. Traction improved greatly w/o rear bar.

Called GW back and spoke with someone who was also helpful, and changed my order!

If you speak to 3 people you'll typically get 3 different answers. Present company not included!

Thanks for the help David additional input on bar diameter vs spring rate would be appreciated. SS.

[railing68]

By the way GW recommended a 800lb spring with a 1" bar.
I went with 680lb in hopes of being able to retain 1.25" for the time being!

[davidpozzi]

I'll come back later tonight and post somethng, have company right now.
David

[davidpozzi]

Springs do very little in terms of roll resistance and oversteer/understeer. The Anti-roll bars do much more. Use the springs to control dive and squat.

I'd say a 465 coil is very very marginal for autocross unless the car is close to stock ride height. Did the front suspension feel like it was bottoming out under braking or corner entry?

A 600 lb coil is a pretty good choice.

Where did the anti-roll bars come from? Adco?

How balanced was the handling with the rear bar connected?
David

[railing68]

No bottoming but it does pull the front tires off the ground under hard accelleration and some 1-2shifts! probably on corner exit ( I was told this by several friends and spectators). Accoriding to GW this is a stiff bar and softer spring however the car seems pretty darn rigid. THe coils are lowered (H.O. claims the low rate). Ride ht is lowered approx 2" all four corners.

Bars are Suspension Techniques, I have had them for a long time, since the late eighties.

1.25" front solid and 7/8 rear.

I am considering re-installing the rear but I will probably have to weld the shackle to the housing to stop the rotation.

I realize their are several variables but are the Hotchkis leafs at 150-180lb enough spring to work well with the new 680lb front?

I can't really completely answer the balance question since I only was able to make 4 runs with race tires with rear bar and weather was marginal for two. It did feel better in the slalom, maybe a bit more agile! Yet traction was'nt great.

Seems there is a debate about whether the first gen should use a rear bar or not.

I am wondering if the stiffer coils will change wt transfer and help keep the front tires more planted.

I just don't want to throw money at it and not make improvements.

Sorry for all the questions, I appreciate the help. SS

[davidpozzi]

How is the body lean at this time?
Although running without a rear bar is "ideal". Some of that approach comes from Dick Guldstrand.

Long ago I purchased leaf springs from Guldstrand and they have solid bronze bushings in the front and rear spring eyes. This stiffens the rear in roll similar to an anti-roll bar, this may be the reason rear bars were seen as bad.

Global West has Del-A-Lum bushings for leaf springs that will do the same thing. Above that, they have the Cat5 which eliminates the spring roll stiffness problem completely. Anyway, I find that a rear bar is needed for most situations. It's against what I've allways heard from the "experts" but on my 67 Camaro and my wife's 73 Camaro, they both needed a rear bar to balance them out with 600 to 700 front springs and 175 rear springs. FYI, we switched from Hotchkis 175 rears with rubber bushings, to GW Cat5 with 240 lbs/in and the same Hotchkis rear bar was needed to balance it! We lost roll stiffness from the bushings with the Cat5, but gained it back in the extra spring rate, making a 0 net difference in roll stiffness only.

I don't see how you are not bouncing off the front bumpstops pretty often unless your tires are not gripping well. Lifting the inside front wheel is a sign the front suspension is too stiff in roll relative to the rear. Our 73 Camaro was doing the same thing before we hooked up the rear bar for our most ecient event.

Corner exit traction is reduced as you stiffen the rear bar, but if your rear bar is so large as to get you into oversteer, then you should soften it, or increase the front bar stiffness. There will always be tradeoffs in this area. If you use the 680 front coils with rear bar, the balance will be better with the rear bar on, and I'd work from there to get it close to neutral balance in long sweeper corners where you are using just light throttle.

With careful fitting you should be able to squeeze a 275-40-17 rear tire on your car. The 245's are marginal for your power level.

A couple of notes:
1. make any handling balance observations in second gear or above, first gear will oversteer in almost EVERY case! Don't waste your time thinking about what it's doing in first gear. Look at Second gear if it's in the 40 to 60 mph range, at mid corner in a sweeper, if you are gently on the throttle to maintain speed, is the front or rear having trouble with grip?

2. Anti-roll bars can be softened by loosening the end link nuts a bit, or substituting rubber end link bushings for polly. Don't overtorque the end link nuts, it can bind the suspension and make it worse. Even more stiffness can be achieved by making aluminum frame mount blocks insted of rubber or polly mounts. You don't need this, because your front bar is already very large.

[railing68]

Thanks for the detailed response,

Lean isn't excessive at all and after watching some videos to confirm this.
However it was really planting the rear and pushing the front in some cases especially in 1st. Noticed more in the rear but understeer increased w/o bar also!

The front bar end links are short due to lowered ride ht, I will be substituting rubber in an attempt to soften the bar, possibly loosening/lengthening slightly( not much room there).

I am wondering if the stiff bar could be limiting the transition and preventing bottoming?

I will replace the rear bar with the current poly end links and give it a go. I am hoping the GW springs come in at the same ride ht since the stance was nearly perfect and no tire rub.

I bought 245-45s so I could rotate front to back since the fronts wear fast in auto-x.

275-40 would be ideal for the rear but require more backspacing somewhere around 5"-5.5"?

I already have solid body mounts, So I guess I will run what I have with the new coils and play with tire pressures. 4 runs is never enough to sort out issues.

SS.

[davidpozzi]

TC member CarlC has put 275's all the way around on a 68. http://www.geocities.com/casanoc/
It requires tubular upper arms for clearance, and the tires will hit the subframe at full lock but the lower arms he used have adjustable steering stops.

I ran a 550 front coil and it was too soft. I don't recall it bottoming out in front with those coils though. I already had the Guldstrand rear leafs but the 550 front coils allowed too much weight transfer front to rear and buried the rear so low on hard acceleration that the pinion hit the rubber bumper on the unibody. Changing to coils close to 700 fixed it. Your stiffer front bar may be helping you keep off the bumpstops, but as you said you haven't run it many times yet.

Check that your antiroll bar arms in front are close to level. If not, shorten the sleeves to get them closer to level and don't over torque the end links. Don't get them fully level because it may require shortening the sleeves too much and the sleeves need to move side to side actually more than they move front to rear. If the front bar is not correctly installed, it can hold the front end up and even bind. Look closely at the very ends of the bar, the bar to end link bolt angle should be pretty close to 90 degrees. Any other part of the bar does not matter.

I haven't had much luck playing with tire pressures, the radial tires are not as sensitive to it. With your tires I'd put 40 front and 36 to 38 rear for a start. If the course were tight with lots of decreasing radius turns, I'd go up 4 or 5 lbs. If the course were more open and flowing without severe left/right turns, I'd lower pressures 4 or 5 lbs. The main thing is to prevent front tire roll-over on the sidewall. Some people put dabs of white shoe polish on the tire shoulder to show if the tire is rolling over and how far.
David

[davidpozzi]

Our rear bar slipped too. I tightened it more this time, but if it moves again I have two ways of making it stay put. One is to tack weld it in place. The other is to tack weld a piece of metal in front and behind the mounts, that way I can still unbolt and remove the brackets.

David