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Spring rate trade offs

M

matt5112

New member
Heres the suspension setup so far:

Bilstein HD's.
Vogltand springs spring rates: 200/140
Dorman front sway bar, 33 mm solid.
ADDCO rear sway bar, 22 mm solid.
GMPP trailing arms.

Things that dont matter:

ZZP STB's, poly sway bar bushings and front end links. Moog rear links.


Its not comfort I'm concerned with at all.

I wouldn't care if it the car beats me up all the time.

Yes, have been in cars that do that for extended periods of time and driven them.

Car is already a little harsh on the bumps.

ZZP ships their coilovers with 350/275 spring rates.

I think this will be a little high for maintaining traction on the rough roads that we have around here.

I'm thinking a nicer compromise would be 275/200.

Similar increase as going from stock (143/120) to the vogtlands.

Just need to talk to more people running spring rates that high.
 
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Re: Spring dimension anyone?

my coilovers have 7 kg/mm front, 5 kg/mm rear. that equates to about 390 lbs/in front, 280 lbs/in rear. it was a rough ride, but then again my struts were probably valved by retarded people. handled pretty well, though.

doing it again for a better handling car that i could keep off the ground more readily i would jump up to 8k/6k (~450lb/335lb) like most of the aftermarket coilover manufacturers use for my car.

knowing that the grand prix is a heavier car with a lot more load to shift around, would you consider going higher than your initial numbers?
 
Re: Spring dimension anyone?

I need to know the sprung weight of the vehicle.

McPherson strut though right?

With that you can get the ideal cycles per second.

Interesting to note the stock CPS has a rearward bias to help with understeer.

Regardless, how was traction on rougher roads? Non-existent?
 
Re: Spring dimension anyone?

yes, mcpherson strut.

traction on rougher roads did kinda suck, but ill admit i never pushed it really hard. i did take a few left hand turns through lights at a couple rough intersections and the car seemed extremely unstable because of its ability to take flight due to the spring rates. however, on flat roads (on/off ramps for the highway) it worked pretty nicely. my new spring/strut setup would be no match for it prior to the swap on a little road racing course.
 
Re: Spring dimension anyone?

knowing that the car has a natural tendency to understeer A LOT, i would probably opt to bumping the rear spring rates more than you'd be bumping up the front. that, applied with a bigger rear sway bar may be able to cure a lot of the handling issues this car is famous for.

however, since youre trying to keep the rates light to trade off handling for ride comfort im not sure this arguement is worth having.
 


my car is a little more balanced and the RWD bias of the AWD system does lend itself to being able to run higher rear spring rates, i agree with you there.

however, i think the same concepts would help out, even on a FWD car. right now you have a car that cant get the ass end of the car around to save its own life. bigger, stiffer everything in the back would help this situation out.
 
honestly the best thing to help out this car would be a subframe brace, but no one is going to take the time to make one.
 


Wrong about:
but no one is going to take the time to make one.
Click to expand...

problem is: lack of ground clearance and the odd way the rails are recessed in the rear.

Also a roll cage is typically designed to reinforce the points that are connected on the under body.

Makes a proper one very difficult, and expensive.

I believe nick had some plans for your most simplistic SFC's though.

front subframe to trailing arm mounting location.

Rear subframe is so far recessed its pretty difficult to get in there, again, utilize roll cage for that portion.


Comes down to money really.

It'd be cool, but is the investment worth it.

Funny I say that considering the parts I already have into it haha.
 
As far as spring rates go, I started with a 375, and it made the car a "little" tail happy in the faster turns, right now I am running 275 and it seems good. Really, the ride quality didn't change much with the spring rate change, it just made the overall balance a little better. After I get the front coilovers done, I am going to prob think it is crap though, good thing I can get all the springs i want for free! I did find that the dorman front sway bar really stiffened up the front, and helped the balance a lot! I plan on doing a top swap in the very near future, so I can't really give you much feedback on the front spring rates until I get that done, but after the top swap, the front coilovers are number one priority.
 


yeah, i am thinking that my front is "ok" for now. I wanna get the top swap done and maybe a cam and other engine mods first, so I can whoop up on my buddy's earnhardt jr monte, since he wont shut up that his is faster on the top end. we ran and i kept with him to about 40, but after that his sc helped him pull away, and he doesn't believe that i will ever be able to stomp him lol:th_laugh-pointup:
 
Not sure how much it honestly helped because I did it all at once.

The rear STB seems to help a little for chassis flex. Maybe that's a first low cost step to see if something in the trunk could help the issue.

The other things I did were to oversize and poly the toe link and lateral arm. Those typically flex a lot from the factory.
 
BillBoost37 said:
Maybe that's a first low cost step to see if something in the trunk could help the issue.
Click to expand...


That makes me things. A lot of the older RWD cars have cross braces behind the backseat to provide structural support and prevent body flex and roll. That could be a possibility.
 
when i put my next one together i planned on deleting the rear seats and putting in a half cage to stiffen up the mid section of the car. most likely i would bind this cage to the rear end of the car in some fashion.
 
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