Rear spring rate recommendations

[rattus]

I'm having a somewhat difficult time deciding on what leaf springs I should run on my 69 firebird. This car will rarely be driven on the street so I'm not concerned w/ a smooth comfortable ride, but w/ some compromise between drag strip and road coarse performance. I'd like the springs to be sufficient to control wheel hop w/ out using traction devices, e.g. Caltracs, etc. I'm making 450-500 rwhp.

I've searched this and several other boards regarding rear leaf spring rates, but the info is pretty sparse on recommended rates. From what I've found there are a few "off the shelf" options and a few custom options:



Guldstrand, DSE, Hotchkis, Global West: all seem to be in the 175lb/in range. It seems that most people are using these, but some have stated that these are a little too light for the track (and require traction bars etc.).

Afco, Landrum, etc. offer several springs in the 200-250lb/in range, w/ various true arch heights.

Landrum offers a "drag race" multi-leaf 300 lb/in w/ custom true arch. They will also custom make higher rates.

Flex-A-Form and Hyperco offer composite mono-leafs in the 200-250lb/in range. One guy on cc.com has the Flex-A-Forms and really likes them. Hyperco recommends using a panhard bar / watt's link.

The composite leafs seem appealing due to the sprung weight savings (which could offset the weight added by panhard bar / watt's link).

Without much experience, I have the impression that the 250-300+ lb/in range will work well.

Also I plan to use either Guldstrand solid (bronze) or Global West Del-a-lum bushings.

[Reckn8]

I am also interested in the composite springs and am wondering what spring rate to order. Any help??

[Lowend]

In general I would stay away from the fiberglass springs. They have strength issues in hotchkis style mounting, ie they shatter.
Every 'glass spring I have come across need a custom valved shock with extra rebound damping to work properly.

In general 160-180 lbs should do you pretty well. IMHO the Global West L2CatV is the best spring out there

[CarlC]

What is the cause of the composite spring failures? Torsion? Heat? Front section compression? Damage?

[TitoJones]

I too would like to know of the fiberglass failures. After hearing of that Torker did on his Camaro, I'm interested to see if these would be good for a road race application.

Tyler

[zbugger]

I have heard that it's fatigue. They are not recommended much for drag racing because of the repeated hard launches. I'd think that for a road race application it would be ok, but the shock choice would be important.

[Lowend]

The fiberglass springs work ok in Vettes because they are transverse mounted and do not take the full force of the torque. From what I have seen the fiberglass springs can deflect sideways to extremes which causes them to split lengthwise
Look at VBP's website, they even say that the springs should not be used with over 400HP.

[Chevy350]

As a trivia, thought I'd throw it in here;
From the time I worked at the local Chevy dealer over here, I remember the Astro vans with composite rear leafs cracking all the time right where the axle is mounted. They were all converted to regular multi-leaf springs. The power from the 4.3L V6s isn't that great, so I guess it's more of a weight issue on the light trucks.

[chicane67]

Your rear rate is going to be dependant on a few things..... mainly front rate, FE geometry changes (if any), sta-bar, shock valving and chassis weight.

But, specifically your front rate and any geometry changes done to the front suspension. Your impression of a 250-300 rear rate would put you in the 700-720+ front rate to even be a close balance.

You can purchase higher rate springs (than what is advertised) from Guldstrand, specifically his FIA spring that rolls in at around 275.... but you will only get the small diameter bronze bushing in the front eye. Nice thing is, at least that spring has a partial wrap on the front main eye that acts as a traction bar.

When I worked for ole Dickie Poo Guldstrand I got a lot of time in on building various designs. What I am sure of is that you will definately want a partial wrap on the front main eye, a reverse rear eye (for the ride height benifit) and using various leaf lengths to control brake hop and to control the instant center location.

I myself am using a design I whipped (with the influence of Guldstrand pushing me along) and came up with a 720/320 package that works like a dream. I have even done a few dozen sets for clients chassis that were built to the specific client chassis.

The only down side, is the cost of American spring steel in the current market.

If you want, PM me with your e-mail and I'll send you the spec/build sheet. The design is basically off of the 24hr Daytona spring, but with some late tech throw-in.

[DLinson]

Chicane,

What are the ride frequencies for the car with the 720/320 spring set-up? Is that on a track only car? Would you consider it for something that would see street duty?

Thanks,
Dennis

[chicane67]

Dennis,

The chassis saw double duty on the street (as a daily driver) for 3+ years and was driven hard (understated) on and off the street with the noted spring package. I myself, am more than pleased on the balance of the chassis as it is. So yeah, Id run on the street without hesitation.

The coinciding shock package was 350/160 front and 275/110 rear and the front sta-bar is a 0.750" with no rear.

I should note that my 67 weights in under 3k and the chassis is a little more on the exotic side, so the related freq is going to look a little firm. I don't believe my set-up is going to yield the freq numbers for a typical 67 chassis with a 720/320 package. The last time I ran the numbers was awhile ago and I have made some changes to the chassis (since the last time I even dealt with actually "doing the math") so I am only able to supply you with a rough. I would say its around 2.1F/2.3R to 2.3F/2.5R. I think its on the latter side of that rough, but the choice of bushings and the dampers did change its perception of ride quality tremendously. Its compliant yet it takes high speed compression very, very well.

.......I cant say enough about Del-a-lums and a properly valved set of Bilsteins.

[shmoov69]

I have had the Vette Brakes composite springs on my car since about '91 and have been very happy with them. It has not been a powerhouse until about 5 years ago though. No signs of problems still. At the track it is low 11's, high 10's with 1.60 60' times. They seem to be fine, but I don't know about the benifits in handling or the such since I was in high school when I got them and pulled the stock monoleafs out. It was night and day difference then!

[Lowend]

There is a guy that goes by ovrsteer at 2GCOG that has video of the fibglass springs in his CP car deflecting a fell inch to the side during cornering