Front suspension - what weight springs?

750hp · #1 (**permalink**) 08-12-2001, 04:50 AM

I was hoping to borrow a few sets of front springs to test what best suited my car, but to no avail...

I was thinking somewhere around the 375lb mark - am I in the ballpark?

(Vehicle weight around 2400lb, front-rear distribution unknown

)

Thanks for any opinions.

750hp · #2 (**permalink**) 08-12-2001, 05:33 AM

Replying to my own post! I have had a look at the calculators on Richard Hudgins' JBL website, so I know I'll have to make compensations for the spring mounting angle, control arm to inner pivot ratio etc, but I'm really interested in the "desired ball joint rate" as mentioned in those calculations. From that number I can choose my springs with confidence. I suppose my weight over the front wheels is similar to a big block. I have a 351W with the added weight of a Vortech supercharger and an air to air intercooler.

Richard Hudgins · #3 (**permalink**) 08-12-2001, 09:26 AM

Hi Craig,

It would be my best guess that you would wish to be in the area of 140 for all around use.

Wheel rates for soft street use should be 120-125.

Wheel rates for "sports" type use 135-140.

Road course use (depending on chassis stiffness) 160-180. (stiff chassis) These numbers can be mush higher on a flexible chassis.

Hope this helps a bit.

750hp · #4 (**permalink**) 08-13-2001, 02:50 PM

Thanks Richard! WOW, those numbers are way lower than I was expecting. I thought I had heard guys on here speaking of numbers around the 350-500 mark. I'm glad I asked...

Thanks again,
Craig

Bob Putnam · #5 (**permalink**) 08-13-2001, 03:19 PM

Richard,

Aren't those natural-frequency numbers and not spring rates?

Richard Hudgins · #6 (**permalink**) 08-13-2001, 07:53 PM

Hi Bob,

Correct. I left out the CPS designation. (nothing like confusing the folks with goofy information)

I always design to spring frequency. the numbers that I gave Craig are on the high side as used for sports cars. Standard road cars are lower by 20% or there abouts.

the equation for wheel rate is:

Wheelrate=(motionRatio)2 X spring rate.

For instance the rear of the JBL is as follows:

142.56 (LBS)= .5184 X 275

I would think the front wheel rates in the area of 275-325(LBS) would be correct for most Cobras.

Sorry for the confusion.

wadesdad · #7 (**permalink**) 08-13-2001, 08:10 PM

Just picked up my pieces parts. Springs for my coil-overs are
Carreras (Atlanta, GA) : P/N 10CS400
"Coil Spring, 21/2" I.D. 10" Free length, 400# Rate Chrome Plated"

Zderf · #8 (**permalink**) 08-14-2001, 07:19 AM

My Can Am big block weighs in at 2475#. Distribution is unknown. I had 450# springs all around and it rode like a lumber wagon with a threaded rod suspension. I recently installed 350# Alden adjustable aluminum coil overs all round. With some adjusment of the spring, I achieved my desired ride height and now enjoy a ride that actually has some suspension. The shocks are set midway in the recoil scale.

If your planning on moderate hiway and cruising use, you would likely find the 350# springs to be good. Anything over 350# may be a tad stiff, especially since you are not running a big block. But every car is different.

Good Luck.

Zderf