Question: 65 Barracuda Swaping from leaf to coilover what spring Rate?

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MonkeyMadness

MonkeyMadness

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Hello,
Just as the title says, I'm looking for a "ball Park" spring rate. I've ditched the leafs and straight axel set up. I have a set of Jag spring over shocks on the car for mockup/ build but now I need to get a proper spring rate on the rear.
The car setup is HDK frontend with QA1 coilovers, V8 with heavy over/drive auto, and out back I have a full XJ12 jag IRS setup.
The cars intent is mostly cruse and lively drivability, and the occasional road Rally

Thanks
j
 
Got pics of the Jag setup ?
 
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Uh, it's more complicated than that. Your Jag IRS will have a motion ratio associated with it, so the spring rate for the factory leaf springs will be no where near the spring rate for the coils if you want to keep the wheel rates the same.

The factory leaf spring rates were 90 lb/in for the /6 springs and 110 lb/in for the factory XHD's. And note those are spring rates, not wheel rates.

Here's a video on how to calculate it. The example car in the video is a Mustang so it's not going from leafs to coils, but going live axle to IRS on that car meant going from 450lb/in springs to 806 lb/in springs to keep the wheel rate the same.


For example, a lot of the club Cobra guys run 250lb springs on their jag IRS set ups. Those cars weigh like 2,200 lbs, so you're gonna need more than that.
 
72bluNblu said:
Uh, it's more complicated than that. Your Jag IRS will have a motion ratio associated with it, so the spring rate for the factory leaf springs will be no where near the spring rate for the coils if you want to keep the wheel rates the same.

The factory leaf spring rates were 90 lb/in for the /6 springs and 110 lb/in for the factory XHD's. And note those are spring rates, not wheel rates.

Here's a video on how to calculate it. The example car in the video is a Mustang so it's not going from leafs to coils, but going live axle to IRS on that car meant going from 450lb/in springs to 806 lb/in springs to keep the wheel rate the same.


For example, a lot of the club Cobra guys run 250lb springs on their jag IRS set ups. Those cars weigh like 2,200 lbs, so you're gonna need more than that.
Click to expand...


Thank you! This was perfect and exactly what I was looking for!
 
MonkeyMadness said:
Hello,
Just as the title says, I'm looking for a "ball Park" spring rate. I've ditched the leafs and straight axel set up. I have a set of Jag spring over shocks on the car for mockup/ build but now I need to get a proper spring rate on the rear.
The car setup is HDK frontend with QA1 coilovers, V8 with heavy over/drive auto, and out back I have a full XJ12 jag IRS setup.
The cars intent is mostly cruse and lively drivability, and the occasional road Rally

Thanks
j
Click to expand...

I`ve got a pair of 350# , and a paqir of 500# springs for 12'' shocks , if u can use either of them ----
 
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