My question concerns the spring rate of my HO coils and the suspensions techniques bars I have. The bars are solid 1-1/4 and 7/8 rear, coil rates are 470lb. Since I have solid bars can I use a softer spring rate like these? Hotchkis 3 leafs in rear variable rate to 180lb I think. The stance of the car with these coils seems really good. From what I have read on davids suspension site is 650-700 would be ideal, how much does the bar play into this equation? The intended use is autocross.

[ 04-15-2003, 04:03 PM: Message edited by: railing68 ]

Those thick bars would be too stiff for a 650-700 spring. They are better for a stock spring or maybe OK for the 470 coils you have.

The problem to look for is excessive front lift or dive. Your thick bars will make the car corner level, but the softer rate of the coils will tend to allow excessive front lift and rear squat. The front lift really affects rear squat a lot.

The amount of traction your car can produce will determine how much lift and squat you generate to load/unload the springs. If your tires are skinny or hard, the car won't generate enoug G force in acceleration or braking to show up soft spring problems. If you put slicks on the car with wide rims, you may find the rear suspension bottoming out when on the gas, and the front hitting the bump stops when braking. If that happens, it's time for stiffer springs and then you may need to soften the bars to keep the car from skating in the corners.

If you do plan on using the softer coils, allow for a little extra suspension travel to help it out.
David

good question/topic railing,
i'm looking at new front springs for my 69 also.
david, what would you think of 550 lb fronts with a 1 inch solid sway, aluminum headed smallblock, gulstrand mod, 17" rims with 40 series. no rear sway bar. rear spring rate yet to be determined.
would this be a decent match for autocrossing?
thanks
kip

David won't the front sway bar limit lift to an extent, due to the end links? I seem to remember several cars at the drags disconnecting links for more weight transfer. When choosing end link lengths shouldn't the distance be based on the bar being horizontal and the suspension at rest? How much does link length matter? I spaced the bar off the frame previously to get it away from the balancer, which in turn shortened the link length. Does this have a positive or neg effect on the suspension? Also what are indicators of not needing to run rear sway-bar, Since the set is matched I am going to try both together. I used to run both with suspension in stock form, spring rate is increased now with Hotchkis in rear and Bilsteins all the way around I have up on your site about rear bars somewhat but I am not sure which way to go.

Kip,
My buddy has a 69 with those springs and front bar (Addco) He has 245-45-16 fronts and the car is pretty neutral when I drove it but I didn't get a chance to really slide it around as we were just driving around town.
He had the rear bar on it way before I drove it, but took it off to clear the exhaust or something...

The Addco rear bar has such long arms on it that it has a really low rate anyway.

The more traction you have overall, the more a rear bar may be needed.
You can test for the need by driving in a large 200' circle on flat pavement like a parking lot "skidpad" or freeway offramp with no throttle or brake, do you have to steer into the turn more or out of the turn more when you get to the limit?

If you see you are steering into the turn more, you are understeering, if steering out of the turn, you have oversteer. Adding power or brake masks the result.

railings68,
Yes the front bar can limit lift if the bushings are tight at the frame mounts, also the end links can bind, but would limit dive more than lift due to the arms being elevated at normal ride height. If you use a hard polly or aluminum bushing material and/or loosen the squeeze on the bushing it should allow freer rotation of the bar. See if you can shim a polly bushing bracket away from the frame just a little to loosen it. Polish and lube the bar where the bushing fits. Alternatively, you could trim the part of the bushing that hits the frame and that would loosen the squeeze on it. If you trim it too much, it may wiggle out of the bracket. It can't go outboard as the bar bends there, but it could go inboard. A hose clamp or somthing there would help but it shouldn't be that loose to start with.

You can make a mount out of an aluminum block that will have very little friction and is very stiff.

The arms should be level, but on a lowered car the links would need to be cut too short and they also need to swing side to side as the arms move up and down. I think you have to compromise by leaving the endlinks a little on the long side as a compromise. I'd also look at the link bushings and see if you can use smaller diameter bushings to ease binding, or leave them slightly loose and double nut the bolts so they won't fall apart.
Something like three or four turns from normal tight on the end links might help. Herb Adams made a bar with the end links turned up 90 degrees and put heim joints on for end links, - no binding at all.
David

If I jack the front end up and let the lower arms drop the sway-bar rotates freely in the frame mounted bushing and angles down considerably,Does this sound like proper travel? If it would help I could take some pics of the car this week level and jacked up to illustrate my point better. The bar is supension techniques and when I spoke to them several years ago, they said lowering it with spacers on the frame would not hurt anything, I was just concerned since the end links were so short and whether I had to consider full travel of the A-arms.