CadVetteStang
CadVetteStang New Reader
5/1/14 11:34 p.m.

Thunderbird coil springs 489 lbs./ inch. photo 0501141718.jpgI need to know the number of active coils so I can calculate the rate increase when I cut them. One end is square and one is tangential. I think I am supposed to count the tangential end but know not to count the square end.

FYI the current rate is 489 lbs. and the free height is 13.9" I am looking at about 10-11" as a starting point for installation.

Tom Suddard
Tom Suddard Associate Editor
5/1/14 11:43 p.m.

Could you post a picture of the spring compressed in its mounting location?

CadVetteStang
CadVetteStang New Reader
5/1/14 11:57 p.m.

I have the pic edited into the post now. It did not take on the first attempt. Thanks.

Tom Suddard
Tom Suddard Associate Editor
5/2/14 12:05 a.m.

Assuming none of the coils touch each other when it's loaded, I see 8 active coils there. Double-check my work there, though.

CadVetteStang
CadVetteStang New Reader
5/2/14 12:19 a.m.

That makes sense. Thank you very much. They will be installed into an IRS that looks a lot like the SVT Cobra rear end (minus differential and axles). The stock spring (when installed and unloaded) has no touching coils. The 275 lb. Stock springs were designed to be helped by the air shocks, which will be replaced by SVT Cobra shocks. I still have to measure, but I think the motion ratio between the two rear ends are close also. You don't happen to know that ratio for the Cobra IRS would you?

CadVetteStang
CadVetteStang New Reader
5/2/14 12:21 a.m.

BTW ; new here. I am not getting emails when replies are posted. How do you fix that with an Android?

CadVetteStang
CadVetteStang New Reader
5/2/14 12:26 a.m.

Am I correct that with 8 active coils, cutting one full coil makes it a 550 pound spring?

Toyman01
Toyman01 UltimaDork
5/2/14 6:00 a.m.

Cutting a coil should increase the rate by approximately 1/8th. It's too early for math, so you figure it out.

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