Overspendin'

I'm considering the Ground Control weight jack system for my '88 IROC convertible, and I'm wondering about how steetable the system is.
The car is for street use only, which springs should be used to maintain a reasonably comfortable ride without bottoming out during aggresive cornering?
Thanks for any advice!

RegaPlanet

You can get springs made for whatever height you wish but you must keep in mind that the non-weldin weight jacks will add 2" of height. GC can recommend some rates and spring free lengths to you. The system is totally streetable.

To stay near the ride you have now I think you'd be looking at a 650# front and 125# rear. I'm at a more severe level with 850# front springs and 175# rears but I'm even coming down on the front rate as its too much for autox which I do mainly now. I'm thinking of gong to either 750# or 800# fronts with a 10.5" free length. Currently the springs I have now are all 9.5"

I wouldn't be afraid to go as high as 750# fronts and 175# rears depending on what dampers you're thinking of choosing. I'm running regular KYB's right now and cause they're so limply vavled the ride over my regular stock 200,000km RS suspension during normal driving isn't much diff. But once I get the Koni sports I just bought installed I'm sure it'll be tooth jarring on cracked up streets. But I don't mind sacrificing for the performance gain at all. The dampers really do play more of a role in how the car feels comfort-wise over the springs IMO.

Chickenman35

Quote:To stay near the ride you have now I think you'd be looking at a 650# front and 125# rear.

I take it the 125# rear is a typo? Anything less than a 175# rear is going to be way too soft.

I've got the GC ( Suspension Specialist Spring ) 175's in the rera right now and they feel softer than stock IROC rears.

RegaPlanet

no typo, just a guess as to what stock rear rates are.

CrazyHawaiian

The stock rear linear springs are around 100# (102# I think), but usually with the average age of a stock 3rd gen spring it is even lower as they deteriorate and sag over time. Changing the rear spring weight has more effect on the 3rd gen's ride and handling characteristics than changing the front springs. Keep in mind that a harder rate is not always better, but it all depends on the condition of the roads you are racing/driving on. Like building a good engine, a good suspension setup needs a good combo. No single set of parts will make the car handle great. You need a combo of parts that work well together for your desires use of the car. A public street has a high probability of being uneven or bumpy, while a racetrack is usually smooth and well kept. You should keep this in mind when building your suspension. If the car is a street/track car then you need a more well rounded setup than a car that is for track only. Like RegaPlanet said, your dampeners (struts/shocks) play a huge role in the ride quality of your car, and one of the main limiting factors in their ability to dampen is the suspension travel. As you lower the car the suspension travel decreases meaning the dampener has less room to dampen. In the front you can solve this with a set of strut mounts with a raised top that provide more suspension travel. Combined with a set of drop spindles it is possible to drop the front end 3 inches and still retain almost full suspension travel as far as the strut is concerned. But in the rear of the car, there is no solution to provide more suspension travel. This is why changes to the rear have more effect on ride quality than changes to the front. A 175# rear linear spring is a lot stiffer than the stock springs. Thats a good spring rate for street and track use. I'm running a 150# linear 1/2 height spring from Suspension Specialists on my street only 91Z and I wouldnt go any stiffer for a street only car. In fact I might consider that somewhat extreme for street use, but because of my desired ride height for my street car (slammed!) I wanted a spring that was stiff and would lessen the chance of rubbing issue with my wheels and tires. I went this route because my old rear spring setup (Eibach Sportlines) was too soft IMO for the ride height causing a lot of rubbing issues. So far I have had no issues and this is with 18" wheels with 275/35/18 tires. The rest of my setup is a 700# 1/2 height front spring, Koni reds in the front, Tokiko HP's in the rear (using left over parts hehe), and of course the weight jacks. Currently my ride quality is really bumpy but I dont mind it at all (my dad thinks im crazy). I blame it on our junk roads here in Hawaii. I plan to replace my dampeners with the Tokiko Illumina 5 way adjustables. This will allow me to tune the car for a somewhat softer ride that will still not rub. Good for the street.

Overspendin'

Thanks for the advice guys, Crazy...you mentioned drop spindles, I only know of Belltech and I had heard they discontinued production, any other sources?
This car is really a weekend cruiser, I have two kids that will be riding in the back on occasion so I really don't want a suspension that will shake the fillings out of their heads.
I have ordered a set of Boyd Coddington Hot Rods, 18 x 8 front and 18 x 9 rear and have not decided on tires yet.
You have seen the look I am going after on Graboid's car but all things considered I cannot slam the car as severely has he has.
I suppose the ideal solution might be an air ride setup, but I have not been able to find a kit for our cars and don't have the wrench-smarts to engineer my own.
The other components I am planning to order are Spohn's LCA's,
subframe connectors, adjustable panhard rod, urethane bushings etc.
At one time I owned a 240Z with adjustable coilovers, I ran the Tokico Illumina adjustables with that setup and was very pleased with them, would they be a wise choice for this project?

CrazyHawaiian

Belltech has discontinued their drop spindles. I found a website that was advertising them once, but when I emailed them they said they were out of stock indefinately. But you still might be able to catch a used set on Ebay if you're lucky. Thats how Revlimit scored his drop spindles, but so far I have not been lucky enough to find a set. Other companies do make them, SSBC makes them but at the unrealistic price of $1500!! I found another company that advertises custom made spindles so I am working with them to see if they can produce a drop spindle for our cars. Should be under $400. Boyds are good wheels, I'm really happy with my set (18x8 front 18x9.5 rear). I'm running the Potenza S-03 tires and I love them. When you choose your tires be sure to go with a re-inforced sidewall to protect your wheels incase you hit a pothole. As for your suspension, you can either go completely custom with the air suspension, which would be the best of both worlds, or stick with the spring/dampener setup and make a compromise. Unfortunately with a spring/strut/shock setup you cant have a low ride height and super nice ride quality without running into rubbing issues. If you do decide to go with air, contact Easy Street Customs, they make brackets for our cars. I would also contact Air Ride industries and inquire about adapting Easy Street Brackets to their new Air Struts, which are much better for performance applications than Air Bags. Good luck!

Chickenman35

Just a note....no way are the stock springs around a 100lb\in rate. I have rate checked IROC rear springs on a spring checker and they come out at around 170lb\in. There has been discussion on this before...I'll dig up the links later, but right now I have to rush off to a Christmas party. BTW, the rating given in catalogs listed for springs such as Moog,TRW etc doe not equal the true Spring rate as measured by companies such as Eibach, Hypercoil, Afco etc. This is where people are getting confused over spring rate when they order springs from aftermarket companies.

My McQuay Norris catalog ( same as TRW, Moog ) list a rear spring for a 1989 Camaro as Part # RCS5665s. In the catalog this is listed with a Rate LOad Height of 107. Take the same spring...put it on a proper spring checker...and the spring rate comes out around 170lb\in. Go figure...

Checking with Ground Control confirms that to get the equivalent to a Stock rear IROC spring, you have to order a rear spring with a rate of approx 175 lb\in ( Suspension Spring Specialists )

RegaPlanet

So who's got some Z28, IROC/WS6/F41 and RS rear springs to measure diameter and coils so we can solve this riddle?

Chickenman35

Easier to put them on a rate checker.... Unfortunately, with the holidays coming I just don't have the time.

That's why I'm going to proper race car springs. Fed up with this guesswork of springs that are listed as replacements in jobber catalogs. I've can feel a 25lb\in difference in springs in the front of my car. Even less in the rear. Surpisingly, proper race car springs, with a guaranteed rate are very,very affordable. You have to make some changes ( like adjustable ride height ) to the spring perch area, but once that is done, race springs such as Afco, Hypercoil, Suspension Spring Specialists, Eibach etc, are the only way to go IMHO.

CrazyHawaiian

The ride difference between my stock 89 RS with stock springs and my 91 Z with 150# SSP is way different. Granted the stock 89 springs are probably deteriorated and I have no way to measure these springs, it is possible that the stock springs were harder than 107#. If anything I'm thinking I might have confused the rate load height with the spring rate, but now I'm not sure what to say. From my experience my stock 89 RS was the softest, the 91Z with rear eiback sportlines was a little stiffer (but a progressive rate spring so does not really count since nobody knows what the actual rates are), and the 150# SSP springs being the stiffest. If the stock rear spring were really 175# spring rates then I would be very very supprised. Cuz I'm running 150# and its really stiff (with both 16's and 55 sidewall, and 18's with 35 sidewall). Hope we can find an answer.

Chickenman35

I think in the New Year I will try and gather up some rear springs and rate check them. No promises on when I can do this....but I really want to find out what's going on too. One of the things that has crossed my mind is that the Suspension Specialist Springs that I got were somehow tagged wrong. They're suppossed to be 175lb\in...but were softer than the Iroc springs that I took out.

It's very confusing.....

Everything works out just fine if you order a set of springs from one mfg. Lets say Moog or TRW...but their load rates do not seem to coincide with " spring rates " by such mfg's such as Eibach, Afco, Hypercoils or Suspension Spring Specialists. So comparing one to another is like comparing Apples to Oranges....or maybe a better comparison is between Camshaft profiles before Mfg statred using the .050" standard. Some mfg's would use a .020" checking figure, some would use a .006" checking figure etc, etc. It drove you nuts. Same thing with the spring situation...... Grrrrr

RegaPlanet

that'd be great chickenman.

I plan on running half of my next season of autox with these koni sports and a properly setup rear(posi, brake biasing and relocation brackets) to see how the car feels before I try some other springs. But so far from what I've been reading I'm thinking of going to a softer spring in front(750 or 800) instead of raising the rear rate to balance the car(current setup in sig). I do have my mind set on the road courses mind you. The autox is just a stepping stone.