coil over spring rates.David P or ? - Team Camaro Tech
Brakes, Suspension & Steering Conversion questions, Steering & Handling

 
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post #1 of 9 (permalink) Old Feb 24th, 02, 08:15 PM Thread Starter
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David,

I did a search and found several times where you talked about a 500-650 pound per inch front coil spring on these cars for handling. How does that compare to a coil over spring? I'm guessing it's not a direct comparison. I am just finishing up a Wayne Due conversion with Bilstein coil overs on the front. The springs were 500 pounds per inch. I have an all aluminum big block with a centrifugal blower and A/C. Less weight than a standard iron big block but with the accessories probably heavier than a small block. You can't even compress the front suspension, literally! It rides like a skateboard and is basically undriveable on the street. I'm guessing I need 400 pound springs or maybe even less. I want good handling but can't live with a super stiff suspension.

Do you use different spring rates when comparing regular coil springs to coil overs? What would you recommend?

Thanks for your time.

Jody
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post #2 of 9 (permalink) Old Feb 24th, 02, 08:25 PM
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David Pozzi
 
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Jody,
The secret is the mounting location and angle.
You need to first figure what the spring rate is at the WHEEL.
Then figure what spring will give that rate with the new setup.

Coil overs usually are mounted very near the ball joint for better control. If yours are that way, you need a softer spring to achieve the same wheel rate as a stiff spring mounted farther from the ball joint like on a first gen.

A 550 lb spring gives a wheel rate around 325 lbs per inch.

*** Correction*** the wheel rate is 178 lbs per inch.

If you can measure from:
lower A frame inner pivot to ball joint, and from inner pivot to lower shock mount, give me those dimensions.
Also I need a measurement from shock centerline to lower A frame mount as viewed from the front. It must be measured in a 90 degree angle from the shock.
If you have trouble with that, just measure the shock angle in degrees.
I'll try to figue a new rate for you.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 Origonal owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

[This message has been edited by davidpozzi (edited 02-25-2002).]
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post #3 of 9 (permalink) Old Feb 25th, 02, 06:57 AM Thread Starter
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David,

Thanks for our help. I'm a softer spring/more shock kinda guy and this thing is unreal. I can't compress the front suspension by pushing down on it; it just kinda wiggles a little..

The a-arm pivot centerline to lower ball joint centerline is 13.5". The a-arm pivot centerline to lower shock mount center is 11.25". The shocks are at a 70 degree angle at rest. The last measurement I was not totally sure of what you wanted, but I measured from the centerline of the shock 90 degrees to the centerline of the a-arm pivot; it's 10.5".

These are as close as I can get; it's pretty crowded in there. They are Bilstein coil overs mounted upside-down (spring on bottom, adjuster on top, their recommendation) with 500 pound per inch springs.

Thanks again.

Jody
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post #4 of 9 (permalink) Old Feb 25th, 02, 07:24 AM
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Thanks, that should work for me. The spring is very close to the ball joint and that is giving you more of the spring rate than on a stocker.
This is typical of a coil over mounting and is better as the shock has more travel per inch of wheel travel than on a stocker.

I'll figure out an equivalent spring for you and post it here.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 Origonal owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer
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post #5 of 9 (permalink) Old Feb 25th, 02, 10:55 AM
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I made a mistake and used the wrong multiplier for the eqivalent wheel rate above. A 500 lb spring yields a wheel rate of 178 lbs, not 325.


First Gen ratios:
.596 MR*
*motion ratio, amount shock moves per inch of ball joint/wheel movement.

.356 MR2** 500 lb spring on firstgen 500 X .356 = 178 lbs/in at wheel
**motion ratio squared, converts spring rate in lbs per inch to wheel rate in lbs per inch.


Your ratios:
.777 =MR
.6 = MR2

500 lb spring on your car= 500 X .6 = 300 lbs/in at wheel, what you have now.

1.667 is your MR2 Reciprocal ( reverse of MR2). multiply by this to figure what the desired (178) wheel rate will yeild the needed coilover rate. 178 X 1.667 = 296 lbs/in - the needed "new" coilover rate.
Looks like a 300 lb/in spring will equal a 500 lb spring on a "normal" first gen.

So, let's use your now known present wheel rate (300) and use the stock first gen reciprocal (2.809) to figure out what rate spring would have to be used on a first gen suspension to equal your present wheel rate.
Since your present wheel rate is 300 lbs/in, it would equal: 300 X 2.808 = 842 lbs/in!
So it would take an 842 lbs/in front spring on a stock Camaro to equal the wheel rate you have on your car now.

Hope this helps.
David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 Origonal owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer
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post #6 of 9 (permalink) Old Feb 25th, 02, 11:22 AM Thread Starter
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David,

It helps a bunch and I REALLY appreciate you spending your time to help me. I had decided on a 300 pound spring after talking again to Wayne Due, but I wasn't ordering anything until I heard back from you.

It now makes sense why the car is so stiff!!!!!!

Thanks again.

Jody
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post #7 of 9 (permalink) Old Feb 25th, 02, 01:09 PM
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I am going with the carrera coilover kit and it bolts into the stock shock location. I do not have the coils yet and i was wondering if I should go to a considerably lower spring rate like Camcojb. Was it the mounting location that made the difference?
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post #8 of 9 (permalink) Old Feb 25th, 02, 01:40 PM Thread Starter
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I'm not answering for David, but I believe that is correct. If the springs weren't way outboard next to the ball joints it would have been completely different. If their kit puts the coil over where the stock springs were then you should be able to run a spring rate similar to if the suspension was stock.

Jody
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post #9 of 9 (permalink) Old Feb 25th, 02, 08:49 PM
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Yes, it is the spring leverage difference that makes the difference. It makes a difference in shock valving or effectiveness too.

The 550 range spring is real nice on a street Camaro. Kinda stiff but not as bad as the Hotchkis and Global West rates are.

I had to go stiffer for autocross because I had 10" wide road race tires and under hard acceleration in low gear the rear Guldstrand springs were bottoming out. I think it was the pinion snubber hitting.
With Hotchkis rear springs and normal tires you are probably OK. The Guldstrand rears were special autocross springs and very very low to start with.
If you do experience bottoming out like I did, you may have to go stiffer on the front.
I found going stiffer in front makes a big difference in how the rear squats.
You need to find a front rate and front shock rate that will work for off the line and first gear hook-up.

Tell Wayne I said HI.
David

------------------
Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 Origonal owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer
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