I have a 96 Formula.

To my knowledge it still has the stock suspension setup on it.

I Don't do any road racing with my car at all.

I have some extra stereo equipment in the trunk of my car. I'm not sure of the weight, but I know the speaker box weighs in the neighborhood of 100 pounds or so plus I have an amp rack as well.

Ok, so when my speaker box is in the car, there is about 1 1/2 inches of space between my bump stops and the axle tubes on the rear of the car. It just feels way too low.

The rear end drops between .5 and 1 inch when I put the speaker box in the car.

I am asking you Autocross and Road Racers this question because it seems that you folks are the logical choice to know about springs, spring rates and such.

What I would like to do is to get the rear suspension set up to handle the extra weight without sagging in the rear end. Is a stiffer spring the right thing to do? Drag launch air bags?

I do some occasional drag racing, if this makes a difference.

Also, I am planning to move to some 17x9.5s up front and 17x11s with 315/35-17s in the rear.

Any advice you folks can give would be appreciated!

 

You should look into getting a height adjustable coil over suspension. This way you can raise the rear height to compensate for the weight of the box. Try checking out the Ground Control kit. It's fairly inexpensive (compared to other coil overs) and you can choose your spring rates. Check out Strano.com, prices are like $420 for the springs and adjustable collars.

 

Thanks!

You are the first person to recommend such a setup...

Do the coil-overs replace the stock shocks and supplement the rear springs?

How would the occasional blast down the drag strip be effected by such a setup?

 

You can still run your stock shocks with coil overs but they will replace your stock springs. They have a threaded collar at the base of the spring which will give you the ride height adjustability you need due to the added weight. If you get a spring with near stock rates you shouldn't have any issues with the occasional blast down the drag strip.

 

Thanks for the reply...

Can someone tell me what the stock spring rate is?

 

114 lbs
The $400+ figure he quoted was for both front coliovers and springs and rear adjustable spring perches and springs. If you only wanted to do the rear, it's much cheaper.

 

Since I don't autocross or road race, I originally thought I would have to get new stock springs, and drag launch air bags.

But if I can do the adjustable spring perches in the back and still run it at the strip occasionally (1 trip maybe 4-5 passes per month or every other month), that's cool too.

I was going to go back with stock shocks, so I can go to SLP for the take offs for that, and save some bucks!

Thanks everybody for the advice!

Is there anything I need to do to make sure I don't lift it too far?

 

Ideally, you'd swap in springs of about 8% - 10% higher rate since that stereo equipment is essentially a permanent load. Your ride quality, particularly at highway speeds, should then be about the same as OE without the constant heavy trunk load (it's a front vs rear suspension frequency thing). The slightly stiffer spring will also be better matched to the load in terms of energy (of suspension motion) per unit volume and will be less apt to sag over time.

Norm

 

Thanks everyone!

I spoke with Sam Strano yesterday afternoon and he recommended what he called "weight jackers", or adjustable rear perches for my car as most of you did. He recommended some 125 lb springs with this setup too.

He also said that the parts cost on it is around $200.

He told me that the single biggest improvement I can make to my suspension is to replace my stock DeCarbon shocks with at least some Bilstein HDs... I'm considering that too.

Thanks again everyone...

Once I can get the parts and get them on the car, I'll let everyone know how it turned out.

 

Sam gives the best advice. He's tried it all, you won't be sorry.

 

I have an interesting update on my issue...

I measured at one point back then with the car sitting on a flat level (or nearly so) road. The measurements were as follows:

LF: 26-3/4"
RF: 26-3/4"
LR: 26-3/4"
RR: 26-3/4"

The above measurements were WITH my speaker box in the car and all my "normal, day to day" crap as well. The box made the rear end drop one full inch when in the car.

I bought a set of stock springs off a member of my car club for $30. I figured it was worth a shot to try anyway.

I removed my stock springs from the car and measured from end to end, the overal length of my spring and compared it to his spring. His were 1 full inch longer!

So, I put his stock rear springs in my car, and measure the rear end. Without the box in the car, this is what I came up with:

LR: 28-3/4"
RR: 28-3/4"

After a week, the suspension had settled to 28-1/2" on each side.

Last night, my wife and I put my speaker box back in the car...

The rear dropped to 28" even on both sides.

The car feels to ride a bit firmer and it's going to take a little getting used to.

I've yet to do the fronts, because my understanding is that you have to remove the shocks to do them, so I ordered some replacement shocks for the car now.

I still plan to take Sam's advice, but maybe this will get me through until this spring with tax money comes in.

 

Could the new springs be out of a WS6 or SS???

The stock rate is 114 but the WS6 or SS is 130-180 progressive. That would explain the difference in height and firmness.

 

By the way, how do you like the 3.42's with the A4??

 

The springs are out of a 99 Trans Am, non-WS6 car. Non-1LE also.

The rear spring tags from the factory were gone so I can't tell you the spring code for the new set that I put in.

My old ones were tagged TTH though.

Sam told me there were a whole bunch of different springs used in the F-Bodies, so I assumed that it was just a case of luck of the draw for my use.


As for the 3.42s, I love them! A great gear for street cruising as well as a little drag racing.

I went a best of 14.299 with my 2.73s, then with the change to the 3.42s I went 14.01 bouncing off the rev limiter on the 2-3 upshift.

I need to get my program fixed for that and there is apparently an issue on the 1-2 shift as well. Ion (MadZ28) is confident that he can fix things for me.

 

I'm thinking about going to those from my 3.23's, the update/back rule in my class. I've done all my re-programming for my TC change and it made a world of difference in how the car drives, it's like a totally different car. I'm not really sure if going from 3.23 to 3.42 will be worth the effort and expense though.

I've used Ion too, great guy and he knows what he's doing. I had him do some minor re-programming for the engine side of things.