Opinions on coil spring rates/adjusters and leaf spring bushings

[mike68]

Have a 68 Camaro that I building and I'm looking for any input on my suspension plans. Car will basically just be a street car, but I want it to handle as well as possible. Will be running a iron headed small block and plan to run a 245 or 275 tire up front and 275-315 tire in the back. (I haven't yet decided how much turning radius I want to give up or if I'm going to minitub it.)

I have the following suspension parts now:
Global west upper and lower control arms
ATS spindles
DSE 3" drop rear leafs (i believe these are 175 lb rate)
Hotchkis revalved Bilsteins
ATS/Lee steering box
Hotchkis 1 1/8" front sway bar

I am planning on using the afco adjustable spring spacers and 9.5" front coils. Have done a lot of reading and looking around, and think a spring rate somewhere about 600-650lbs will be good, but would like some opinions. I am a little worried about going too stiff in the front with the springs and fairly large sway bar compared to the somewhat soft rear springs.(Maybe a smaller front sway bar might be better?) I would also like to know if anybody that uses the adjusters has had any problems with the collars moving on a car that gets driven a lot.

I also would appreciate any input on what leaf spring bushings to go with. I have considered either using some spherical bearings (like the cat5 springs), keeping the rubber bushings that are in the front spring eyes and using urethane in the rear, or going with a solid bushing like the del-a-lums. I understand how this will affect how much rear suspension movement ends up twisting the leafs, but I'm not sure what will end up being the most balanced setup. I'm leaning towards the del-a-lum bushings, thinking that stiffening the rear might be the way to go because these spring are a little soft in rate compared to what some guys run.

Any opinions on the whole package are welcome, sorry if this seems like the same kind of question that everybody asks, I've read through all the old posts and know I'm in the ballpark on the front springs and the whole package, but haven't found a lot of discussion about different leaf spring bushings or long term results with the adjusters.
Thanks for any response.

[Twentyover]

WRT paragraph 3, https://www.pro-touring.com/forum/showthread.php?t=52167

Pay attention to posts 2-4 and 8

On point of collateral collar movement during service, I'm thinking of welding a couple nuts around the coil pocket at different heights in the region the collar will sit in service. Run a screw through the nut into one of the slots on the adjustment collar should prevent incidental shifting of the collar.

600-650 lb/in are the numbers I'm hearing for front spring rate. remember this will yield a wheel rate of about a third or quarter of that due to spring distance from the lower arm inboard pivot vs wheel distance from the pivot. If this turns out to be too stiff, a spring change is easy enough and fairly inexpensive.

On rear leaves- I'm planning on using Del-Alum front spring bushes, and starting with rubber rear bushes. If the springs still flex laterally, I'll then add the rear spring del-alum stuff. May run rubber in the street and Glabal West for track days. Not a fan of using monomballs in street service due to wear.

Just my opinion- worth exactly what you're paying for it.

[David Pozzi]

How much horsepower will you have?

[79T/Aman]

on the leaf spring bushing part you got it backwards the front half of the spring is the "control arm" and should articulate, the rear half is the spring and more flexible so run poly or even the Del-a-lums in the shackles

[David Pozzi]

Global West used to have a warning about using solid front leaf eye mounts with soft rear shackle bushings. The leaf will act like a lever and rip out the front clip nuts on the leaf eye bracket. I like a stock front eye mount with Delrin shackle bushings. You could use rubber bushings in the rear leaf eye to reduce bind, then Del-A-Lum in the upper shackle, but I doubt there is much benefit.

If you have 400 hp and street tires a 175 leaf is OK. If you have 600 hp and DOT slicks or 180 treadwear tires in the 315 range, then stiffer rates around 250 are needed. I like a 600lb front spirng.

Minitub the car or you will only be able to run a 255 or 275 rear tire max.

You should get Matched front and rear anti roll bars from the same mfr.

[mike68]

Thanks for the ideas so far.

The motor will be a 406 that should make about 500 hp / 500lb/ft
I'm not sure exactly what tires i want to run yet, going try for a somewhat sticky street tire that I can still get somewhat decent mileage out of. Car will eventually be minitubed and have a 285-315 rear tire, but I may throw on a 275 and drive it for a year or 2 first.

I like the ideas about making the front ajustable without taking it apart, I'm going to look more at that once I get all the parts. As for the spring seat moving around on its own, I was thinking about either welding a nut to the collar and using a set screw to lock it in place, or possibly a second threaded seat turned down as a lock nut. Both of these would be similar to the locking methods used on most coilovers, but I don't know if anything is really needed to lock it in place, hoping that somebody who uses the adjusters could say if they have had any problems with them moving or not.

With the rear I had planned on not using a sway bar to start, and going from there. I have read a lot of opinions on this, some say never to run a rear bar on these cars, others say it is only needed on some cars. My thinking was that without a rear bar or a really stiff leaf it might be good to run a solid bushing in both eyes to stiffen the rear in roll, so that all the twist is done by the leaf spring but i don't know if this is the best way to go. I can see some of the advantages of using the bearings, but would think that they probably work better with a stiffer spring so there isn't excessive roll when cornering. Maybe the simple rubber/urethane bushings are the best in between setup?

I understand it's hard to give definate answers on this, it depends a lot on what exact tires I end up using, different peoples driving styles etc. I fully expect to end up changing some parts around down the road before I end up with my ideal steup, just trying to come up with the best baseline to start with.

[ks71z28]

I have spent 20 years dialing in my car for autocross and track days, and well I haven't got there yet, the competition keeps getting faster, so I keep making changes. If you have never driven the car, get it going and get a feel for it, then add parts as needed. The best suggestion i would give is to buy a "kit" from someone, 1st gens are tricky and need a lot of work. 2nd gens take less, and can be made to handle without putting rock hard springs in the car, which you and your lady will hate BTW. Balance is key, geometry is important, but fun is the objective. If I can be of any help let me know.