Spring Rates & sizes

[Brad1970]

This is for a 1972 Pontiac LeMans:

Front:
Afco 5 1/2" x 9 1/2" 650lb rate


For the Rear Spring rate I'm gonna run about a 225lb or 250lb rate.

What size (example 5 1/2" x 11")? If I'm not mistaken I have to run a pig tail spring in the rear, but not 100% on that. Who makes a spring that is linear for the rear like this in that spring rate?

I want the car to be level & not running at stock height.

The type of suspension setup I'm looking for is sporty enough for a very occasional SCCA Autocross but comfortable enough for excited street driving as this car will be my daily driver.

I don't mind a little sporty feel to the suspension, but not looking to rattle my teeth outta my head or jar my kidneys so hard I pee myself...

Sorry if I've missed anything...

I'm going to be running the Savitske Street Comp 2 plus setup up front & a Global west rear adjustable setup.

Maybe Bilstien HD shocks or a single adjustable shocks...

[Roadbuster]

This is for a 1972 Pontiac LeMans:

Front:
Afco 5 1/2" x 9 1/2" 650lb rate


For the Rear Spring rate I'm gonna run about a 225lb or 250lb rate.

What size (example 5 1/2" x 11")? If I'm not mistaken I have to run a pig tail spring in the rear, but not 100% on that. Who makes a spring that is linear for the rear like this in that spring rate?

I want the car to be level & not running at stock height.

The type of suspension setup I'm looking for is sporty enough for a very occasional SCCA Autocross but comfortable enough for excited street driving as this car will be my daily driver.

I don't mind a little sporty feel to the suspension, but not looking to rattle my teeth outta my head or jar my kidneys so hard I pee myself...

Sorry if I've missed anything...

I'm going to be running the Savitske Street Comp 2 plus setup up front & a Global west rear adjustable setup.

Maybe Bilstien HD shocks or a single adjustable shocks...

You might want to consider a lower rear spring rate. I think you will get that kidney problem with the rear rate at 250lbs! :)

[Randy67]

The 250 lb shouldn't be a harsh ride, as my El Camino currently has 350 lb rear springs (5.5" x 11", single pigtail) and it's not a harsh ride, even with extra heavy valving Pro-Shocks. I do want to try a 225 or 250 spring here soon. The single pigtails do work in the 67-72 cars, but I would attach them to the lower spring perch as they can fall out when jacked up. Zip ties will work as a simple fix, or you can use bolts and washers to do it.
Mark at SC&C said he hasn't needed to run the rear rate any more than 200 lbs on his cars, so you may want to consider running 200 lb springs.

[John Wright]

You need the spring to be stiff enough to support the car, but compliant enough to follow the road contour.....finding that balance is part of the fun....LOL

[Bryce]

also make sure at full droop (during a normal driving condition) you are still supporting the car with the spring.

This means you need to know the corner weight and your wheel to spring movement ratio. Then determine how much droop you want. I designed a limiter to limit droop. Use the equation F=kx. k is the spring rate, x is your intended droop at the spring, F is the force on the spring (corner rate divided by the motion ration).

[Brad1970]

I have no idea what you mean by droop, sorry. Could you explain that a little more? Thanks

[Bryce]

when you lift the car the wheel droops. the wheel hangs. this would also represent the wheel falling in a pothole while driving. Or body roll, one side is under compression and the other is extending, representing droop. I hope that helps.