Carl Fausett

I was not able to find accurate springs rate numbers for the 928 springs, so I thru them all in the car to have them tested commercially.

Thought this information might be interesting to you guys.

The 1979 OEM 928 Springs: STATIC RATE SPRING
Front tested at 215 lbs/inch
Rear tested at 120 lbs/inch

Weltmeister 928 Springs: STATIC RATE SPRING
Front tested at 400 lbs/inch
Rear tested at 245 lbs/inch

Eibach Springs from 928 International: PROGRESSIVE RATE SPRING
Front varied from 399 lbs/inch to 559 lbs/inch near stackup
Rear varied from 285 lbs/inch to 372 lbs/inch near stackup

cobalt

Thanks,

I appreciate the info. I heard the Eibachs were stiffer but didn't know by how much.

Interesting device. I am assuming this is measured by a load cell?

Scott M.

No, measured by a brunette.

Scott

T_MaX

Thanks you for your efforts! I have the Weltmeister on mine, but never knew what the spring rates were advertised as they were PO installed.

What is the static spring height of all the springs tested?

SharkSkin

So the eibachs start out nearly twice as stiff... wow!

DonT

Scott - I knew I could count on you for that observation.

cfc928gt

The Eibach rates came out exactly as they advertise the rates to be, not even a pound off, amazing. I have a set of Weltmeister progressive springs on mine, does anyone know what they were rated? I know they're supposed to be close to the Eibachs...

GlenL

Nice work, Carl.

The question of spring rates has been asked often. We've needed the data.

Thanks.

Carl Fausett

When we started testing the Eibachs, we tested them the same way as the other static springs. Basically, the tester operator pumps the hydraulic jack until they register 100 pounds of force on the spring (so the spring has a pre-load of 100 pounds), then they measure how many pounds they must add to the spring to make it compress 1 inch. That yields the answer like 245 lbs/inch for Weltmeister rear and 400 lbs/inch for Weltmeister front.

When we followed this same procedure for the Eibachs (which is the wrong procedure for a Progressive rate spring) we got 275 lb/inch for the rear, and 365 lb/inch for the front. BUT - a progressive spring has top be continued to be compressed and measurements taken every inch until the spring is within 1" of stacking on itself. As the Eibach compressed, it got stiffer(as you would expect from a progressive-rate spring) and yielded the numbers I posted above.

The Weltmeister springs I tested were static-rate (sometimes called "LINEAR" ).
A progressive-rate Weltmeister spring would be different.

QUESTION: How can you tell whether your springs are Static or Progressive just by looking at them?
ANSWER: Take a look at the two pictures I posted above. A Static-rate spring has no change in the coil windings throughout the entire length of the spring. Same all the way thru - symmetrical. You can see that in picture #2. A progressive rate coil will have a descending-rate of coil windings - see picture #1 - this is how it acts like a "softer" spring on light loads and a "stronger" spring on heavy loads.

QUESTION: What are the benefits of each?
ANSWER: Few of us want to have our teeth jarred into our heads on every bump by racing springs when we are just going to Grandma's house for a visit - yet should we encounter along the trip a really neat and curvy road, its not like you are going to stop and change springs just so you can have a little fun.

Progressive-rate springs offer this compromise, softer on the interstate, harder in the corners.

But you will not find many hardcore performance drivers and racers that like to drive progressive rate springs for the very same reason - the spring rate is constantly changing exponentially. To the racer, this makes performance driving most unsettling. You are in a corner at x g's and force, and you think you could go a little faster.... you apply a little throttle.... and your suspension loads a little more... except now your front springs have changed from say 450 lbs/inch to 500 lbs/inch and the car that was neutral steering is now over-steering and you have an unscheduled off-track excursion!

Racers like predictability at that critical point in the corner - and we desire springs that are truely linear - we test for it! Our suspension-setup software that suggests changes to camber/toe-in/stagger/pre-load/CG/shock rebound/shock compression/anti-roll bars/etc just hates progressive rate springs, and you can see why - They throw a constantly moving variable in the suspension!

My final thought here and then you guys can rip this all to shreds: We sell the Eibach progressive-rate springs and I am happy to do so. They are excellent springs with an excellent track record on many many 928's thoughout the world. A good choice for the spirited street driver who on occasion wants to enjoy a Solo II event (Cone racing) or a DE day. They work very well. Cheap, too - they get a lot done with only having to invest in a single set of springs.

Then when you want to start wheel-to-wheel or Solo I (Time Trial racing) events - you will benefit from a quality performance static spring. We have developed spring perch adapters that allow the 928 to hold all common 2.5" static racing springs - and I will be posting about this shortly in a separate thread.

SharkSkin

Carl, I will be needing springs at some point in the near future... and would be fine with something maybe 20% firmer at most. I'm more interested in firm damping. The roads around here are not all smooth, and I've found compliant suspension to be much more useable. For example, years ago I had a 510 that I put Addco swaybars, gas shocks and Pirellis on(back in the 80's when P6's were worth a damn) and I used to leave other 510s with stiffened suspension in the dust. What spring options are available for someone who wants only a slight increase in stiffness?

Carl Fausett

Maybe, given the pot-holed condition of your roads as you describe them, you are better off with stock springs and get the cornering you want out of Koni's and a stronger pair of swaybars.

If you want more - I can set you up in any spring from 200 lbs/inch to 1000 lbs/inch in 50 pound increments.

T_MaX

What brand of springs would these be?

Would spacers or special spring perches be needed to set-up the car at factory ride height?


Better shocks and heavier "Anti"-sway bars will give you what your looking for. springs will not change your dampering so to speak.

SharkSkin

Carl, thanks for the info. I may just go with stock springs, or maybe the next 50 lb increment, Boge gas shocks, and maybe adjustable droplinks. What is the cost of stock springs vs custom or Eibachs?

Garth S

Carl, You've pretty much described the basic setup I've enjoyed on my '80 and recently added to the S4 - 2x green stripe OEM springs over Konis and 2x brown stripe over Konis respectively on the '80 & '88. I'm a fan of this combo for the application described.
These cars are country road use primarily - with pavement that is far form smooth ( Dave may have more potholes, but I suspect it's a close contest ). To go the next step - will a simple change to Heim jointed drop links on the OEM bars make a felt difference? - either at OEM length or adjusted +/-?. Similarly, does a front bar bushing upgrade do much more than look nice on OEM bars?
To move on to upgraded bars, are they best done in front/rear pairs - or will a front only upgrade be workable for the street? TIA

SharkSkin

Thanks... I understand what does what in suspension very well. I do have to replace my springs though so I can get my ride height back in spec.

Garth,

It's not so much potholes as it is old roads where the pavement has been moved around due to heat, heavy trucks, and weekend racers. I have to give props to the folks who maintain the roads around here... at least potholes get patched fairly quickly!