# Spring rate



## rnoswal (Dec 2, 2007)

I bought an adjustable coil-over system last year for my 2005 GTO. The shocks are one way adjustable either firmer or softer with the adjuster on top of the shock. It also came with springs. They springs are way too firm. The fronts are 7 inch long, 2 1/2 inner diameter. I tested the spring rate on one, knowing they were too stiff for street driving, it was 375 lbs. I remember reading that the stock front spring rate was around 175. 

The rear just came with a shorter coil with an adjuster under it and again, way too stiff. The rear shock is threaded so I am going to try to make it a coil over someday. I also know that where the rear spring is mounted now it has to be a higher rate than if I took it out and made the shock a coil over since it is closer to the wheel and further out from the pivot point. I put my stock ride replacement spring back on to soften the rear but it puts it too high for now. I can live with that for a little while.

I am thinking about putting an 8 inch, 2 1/2 ID, 200 lb rate for the front. I didn't mind the rate of the STOCK front spring but I wanted adjustability. Any thoughts on this and maybe some thoughts on what would be a good street-able combination front and rear? There is no track close by but I like spirited driving.

Thanks

Russ


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## svede1212 (Nov 1, 2005)

IMHO picking a spring height and putting them on is the best solution for 98% of people. You either want it raised (I have no good idea why), stock height or lowered to as far as 20mm (3/4"). Beyond those parameters there are problems with wheel camber and too short of travel. 20mm is I think the best all around. Along with a bushing replacement camber will be good, handling will be improved and the ride won't be compromised. For almost everybody being "adjustable" isn't a benefit. That said I'd sell the set, get some Lovells drop springs and some Koni or other adjustable shocks/struts and be done with it.


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## rnoswal (Dec 2, 2007)

I already have a good coil over system but the springs they sent with the kit are was too stiff for my taste, jarring in fact. The front is 375 lbs linear. It is a 7 in tall spring with a 2 1/2 inner diameter. I bought the coil overs so I could adjust the ride height. I do not need shocks as these are adjustable as are some koni's. 

All I need to know is what the stock spring rates are on any GTO for 20-05. They should all be the same. I don't care about how much drop aftermarket springs offer because I can adjust mine to my taste. I read in one forum that the spring rate stock was 175. Well now that I tried a set of springs that were 200 lbs I now know that that number is way off. The springs coil bind before it even starts to raise the car.

Ride height is one thing but it says nothing about how harsh the ride will be. That has to do with spring rate. This fixation with ride height is strange because even though the car may look good at a certain height, how does it ride? Of course stiffr or soft shocks play into that but that is why I have adjustable shocks to give me the ride quality I am looking for. Corvettes offer variable stiffness with their cars but it is all in the shocks, you can't vary the springs while driving. I could put a solid bar on in place of a shock and get the ride height I want but I would hate the ride.

Anyway, I just thought someone might now about spring rates.

Thanks
Russ


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## AlaGreyGoat (Jul 6, 2006)

Spring weight is per inch. A 200lb/in spring will collapse 4" with a 800lb load, so a 12" long spring will settle at
8", but a 7" spring will settle at 3" (way too low). With a shorter spring, you will have to go with a higher rate to
have suspension travel and a harsher ride.

Larry


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## rnoswal (Dec 2, 2007)

Well I guess it would be great to have a set of scales to figure what the corner weights are. An 8 in spring fits best with this coil over setup. With the adjusters all the way down I only have to compress the spring about a half inch to get the nut started. I suppose there is a mathematical way to figure out what spring weight I need but its been a long time since school. 

The parts store I am getting these springs from is Day Motorsports and they have a good selection. But I am just throwing springs at the car right now. I know a 7 inch 375 lb spring was too strong. And I know an 8 inch 200 lb spring is too light. Its a 200 mile round trip to the store so I guess I need to find a spot to try the new spring after I buy them that is still close to the store. I will probably try closer to a 300 lb next along with a 275 lb too. I know the ride I want but wish there was a quicker and more accurate way to be close.

Thanks
Russ


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## rnoswal (Dec 2, 2007)

ok. Well I finally found out what the numbers meant on the front springs that came with the coil over kit from cx racing. 62.170.007 first is inner diameter, 2.5 inches. 170 is mm tall which is 6.7 inches and the 007 is the spring rate which is 7 kg/mm. Changed to lbs/inch equals 391 lbs spring rate value. 

Wow, that took a lot of homework. The rear springs come out to 9kg/mm or 503 lbs/inch. That is very stiff for the lighter half of the car. Now I understand why the car wants to snap around in a hard corner and why it wanted to push so bad with the stock spring set up.

So now I have the option of either a 350 or 325 spring up front. But I still wish someone knew what the stock spring rate is on the 04 to 06 GTO. I have to look around to see who sells the rear short coil for the adjustable height. 

Thanks
Russ


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