Ground Control Spring Rate Comments

[kheetar]

Browsing through the Suspension threads I have found that many fellow P10 owners are in the process of or already have installed Ground Control Coil-Overs. I'm planning on purchasing a set of GC's for my '96 G20 in the near future, most likely to go along with a set of AGX's. I created this thread to aggregate comments on spring rates, specifically how the car rides, so that I can determine what would be the ideal spring rates for my coil-overs. The popular range seems to be 300-340/225-275. I realize that the spring rate depends on the amount of drop, so that information would be nice, too. In any case, I would appreciate any input from anyone who is willing to give it.
Thanks,
Steve Bielat

[P10DET]

OK, my comments are well known, but in the interest in consolidating the rate info in one place, I'll give it another go.

I am currently running 275/200 in my P10 with AGX dampers at 2/2.

The ride is excellent. It's a little stiff, but you only really notice it over expansion strips and other small hard bumps. It does bottom a little still. I have the front ride height as high as it will go (about a 1" drop). I'd like to go about 0.125-0.250" higher. The rear is set to match.

I originally had 340/275 and I found the ride to be too jiggly for my tastes for a road car. When I drove back from the SE-R National Convention in DC I found the ride with this set-up to be quite good (car was pretty well laden). That is what prompted the switch to 275/200.

I think 300/225 might be a good combo, but I don't know. I also need to play with damper adjustments a bit to see if I can improve the ride a bit more.

[poppy_morenito]

George,

Could you post a picture of your car so we can see what the drop looks like ?

My Intrax say they drop. 1.75 but I tell you the ride over a bump is Disneyland Time. It just looks so sweet.

But When I get the car back on the road, it will be time got GC's to go with my AGX's....

[JustinP10]

I don't know if this will help or not, but here is a picture of my car with GC's to compare to a picture of his car. There was some stuff in the trunk, so it looks a tad lower than it normally is, but it'd pretty close, as teh stiff springs don't sag too much with added weight, or at least i havn't seen them do it yet. These are the 340f/250r springs, and i believe 8"f/7r" The fronts are as low as they go, and the rears are about the same height, maybe a smidge lower, just because of the added weight of my sub and full tank of gas (didn't have the sub when I adjusted everything.) Those wheels, aren't the ones on it now (photoshopped on), but they are copied directly over my existing 16" wheels, the tire you see in the picture is the actual tire on my car (205/45/16 Nitto 555zr).

[kheetar]

Hey Justin - The G looks tight. How does it ride? BTW Are those the wheels from the new Sentra SE-R?

[JustinP10]

Originally posted by kheetar
Hey Justin - The G looks tight. How does it ride? BTW Are those the wheels from the new Sentra SE-R?

It rides very well (I think) And why yes, yes they are. From the Spec V. (gotta love Photoshop)

[P10DET]

Originally posted by poppy_morenito
George,

Could you post a picture of your car so we can see what the drop looks like ?

Yeah, Kerry bought some film for me today, but I wasn't able to get any photos today. Tomorrow I'm off to Dallas to pick up my new project. I'll get some photos soon.

[poppy_morenito]

Originally posted by JustinP10


It rides very well (I think) And why yes, yes they are. From the Spec V. (gotta love Photoshop)

It looks great. Thanks for posting. I have photoshop but never use it. Anything with graphics and stuff scare me.. I have no artistic eye at all.

" I don't know art but I know what I like when I see it " ...

[drockg20]

Can you guys explaine what the spring rate is please?

Also i have kyb agx with intrax springs, yet the ride sucks it bottoms about 50% off the time and it is really a jiggle supension.

I think i nee to upgrade to GC very soo. because i miss my stock tight supension.

PS: please help me. also how much are GC going for and who has the best price on them?

thank you

[kheetar]

The spring rate is basically a measure of the "strength" of the spring. Usually spring rates are given in units of lbs./in. So a spring with a rate of 340 lbs./in. will be compressed by 1 inch when a 340 lb. force is applied to it.

I learned in Physics that the force applied on a spring(and thus the force applied by the spring back on whatever is compressing or stretching it) is directly proportional to the change in length (i.e. F = k*x, where k is a number called the "spring constant" and x is the change in length). This seems logical enough, since the more you compress a spring, the more force it takes to compress it further. So from the units of spring rate we can see that it is the same thing as the spring constant.

Some spring manufacturers, in an effort to make cars ride more comfortably, make their springs so they are wider in the middle. This is called "progressive" spring rates. It makes the spring constant increase as the change in length increases. This is so that the springs will flex more when a small force is applied(e.g. going over a small bump in the road) but as the force increases, the spring will compress less and less(e.g. when you're taking a hard corner).

Dampers(aka. shocks, struts) are there to provide a viscous force(proportional to the speed of the spring's up/down movement) to bring the spring back to its equilibrium length. This is the same kind of force that slows you down when you jump into a pool. Without a damper, a spring would keep oscillating up and down forever(in "Perfect Physics Land"). If you've ever seen a car that takes a bump and then continues to bounce up and down for a while, then you've seen what happens when dampers go bad. Since they help to bring the spring back to its equilibrium length, dampers also make the ride much more comfortable, by preventing the spring from extending beyond equilibrium and kicking you in the butt.

Well that's probably more than you ever wanted to know about car suspension, but I'll be damned if I let that bitch-and-a-half Physics class I took last year go to waste!

Lemme know if you have any questions or if anything I said was wrong, I'm basing this analysis pretty much on equations and intuition.:hehe:

BTW You can get GC's on groupbuycenter.com for $460 shipped.

-Steve B.

[P10DET]

Originally posted by kheetar
Dampers(aka. shocks, struts) are there to provide a viscous force(proportional to the speed of the spring's up/down movement) to bring the spring back to its equilibrium length.

Well, not exactly. Sort of by default though.

The dampers don't bring the spring back to equilibrium length per se. It slows the speed of the suspension down (up and down). By doing that, the spring finds equilibrium more quickly.

[kheetar]

George:

The guy selling the GC's on groupbuycenter.com is telling me they only have "street spec" springs, which translates to 395/300 springrates. I told them those springs would give a pretty stiff ride but he said he talked to Ground Control and they said as long as the shocks are good it should give a comfortable ride. What do you think?

-Steve B.

[JustinP10]

I'm not sure what George will say, but I personally wouldn't go that high on a street car, if you race it at the track alot, then maybe, but on the street that's pretty stiff, but I wouldn't go as far as saying unstreetable, it'd just be stiffer than i'd want for a street driven car.

[P10DET]

Originally posted by kheetar
The guy selling the GC's on groupbuycenter.com is telling me they only have "street spec" springs, which translates to 395/300 springrates. I told them those springs would give a pretty stiff ride but he said he talked to Ground Control and they said as long as the shocks are good it should give a comfortable ride. What do you think?

Ground Control actually recommends 340/250 for the P10. I personally prefer lower.

My guess is the guy selling them is a monkey. Often that's the problem with price shopping.

As for comfortable ride, that is subjective, but I don't think it would be a comfortable ride.

[Beige4dr]

Hey George! Any chance you are interested in swapping your 275/200s for my 300/225s? And can I ask what prices you are seeing for the Koni bumpstops?

Thanks,
Jim