Wayne Due spring rates

[Rsimons]

I have a 67 firebird with Wayne Due C4 front subframe and Wayne Due C4 IRS with QA1 single adjustable coil overs. Car is a convertible with an LS3. What spring rates do you recommend?

[Reckn8]

Have you or are you able to weigh the car?

[Rsimons]

No. Current rates are 550 front and 300 rear. Rear is very bouncy regardless of shock setting.

[Rsimons]

What rates are you running on your 69?

[QA1_Bill]

Hey Rsimons,

Do you know the part numbers of the springs? The part number will tell us the free length and rate. If we know the free length, rate, and loaded (compressed) length, I can help determine if the spring is too stiff, and what you could change to.

EXAMPLE:
If the spring in the rear is a 10HT300 or 10-300 (older part number), that would be a 10" spring with a 300 lb/in spring rate. If it measures 7.5" at ride height, that would mean that the spring is compressing 2.5". Spring displacement (2.5") X Spring Rate (300 lb/in) equals the amount of force on the spring. In this example, that would be 2.5in X 300 lb/in =750 lbs. We generally want to see the spring compress 25-35% of it's free length when the suspension is loaded, so if your spring is only compressing down to 8.5" (1.5" compressed), that would be an indication that it may be a little too stiff for street driving.

If you can get me those measurements, I'll be happy to help out. You can call me anytime, my number is in my signature.

[Rsimons]

Hey Rsimons,

Do you know the part numbers of the springs? The part number will tell us the free length and rate. If we know the free length, rate, and loaded (compressed) length, I can help determine if the spring is too stiff, and what you could change to.

EXAMPLE:
If the spring in the rear is a 10HT300 or 10-300 (older part number), that would be a 10" spring with a 300 lb/in spring rate. If it measures 7.5" at ride height, that would mean that the spring is compressing 2.5". Spring displacement (2.5") X Spring Rate (300 lb/in) equals the amount of force on the spring. In this example, that would be 2.5in X 300 lb/in =750 lbs. We generally want to see the spring compress 25-35% of it's free length when the suspension is loaded, so if your spring is only compressing down to 8.5" (1.5" compressed), that would be an indication that it may be a little too stiff for street driving.

If you can get me those measurements, I'll be happy to help out. You can call me anytime, my number is in my signature.

Thank you for the response. I actually spoke to QA1 tech Tim on the phone, and performed those measurements. Fronts were 10-550, 8" compressed, with 1.5" of exposed thread. I chose to change to 12HT450 based on Tim's advice. Rears are 12-350, with 7.5" compressed length and 2" of exposed thread. I decided to replace those with 12HT450 as well. I'll report back after install with how it worked out.

[QA1_Bill]

Great! Good Ol' Tim. He's a pretty sharp tack. Let us know how it goes!

[Z06vet]

On my wayne due w LS1, I had 475lb front springs w/QA1's. I had 200lb rear springs with ridetech 4 link. I'm sure the IRS has totally different mounting configurations. Bouncy sounds like a valving issue. Maybe you could start with a spring rate used on C4's with coil over conversion as a starting point.