Spring Plate Calculator - Questions

kstylianos · 12:03 PM

I'm planning on installing the spring plates tonight with new 28mm torsion bars, Neatrix bushing and Bilstein Sports. Trying to calculate the correct angle using Will's and Thoms calculator. I know the new Bilsteins will take time to settle to my desired 24.5 height, but want to make sure that I set the initial angle correct.

Here are my parameters:

Weight = 1160kg (it's an 82 SC Targa, correct?)
Static Plate Droop = 3.8 (This is default for Euro Height of 25, I'd like to go 24.5 the rear. Is there a 'better' figure here?)
Rear torsion bar size = 28mm
Weight Distribution = 40/60

Calculated Angle = 23-24 degrees unsprung

These look correct?

Neilk · 04-29-2003, 12:20 PM

Wil's and Thom's calc. works great. Make sure to include the angle of your car on jack stands when you measure the spring plate angle.

Don't be surprised if your car is initially 1" too high. It takes several miles before it will settle all the way down.

kstylianos · 04-29-2003, 12:33 PM

Thanks Neil,

I will take the rake into consideration when measuring the spring plate angle.

Just want to make sure I have the weight and static plate droop figures correct before I continue with the 23-24 angle calculation.

Wil Ferch · 04-29-2003, 12:36 PM

Note that the 3.8" default value is a measurement when the car is back on the ground. If you want to target less than 25" rear fender height...and you seem to want 24.5...then plug-in a value 1/2" less than 3.8"....use 3.3" in the calculator. 1160 kg is 2552 lbs....don't know if this is correct, maybe it is. May 85 Carrera was "spot-on" duplicating it's published weight of 2760 lbs. I'm somewhat troubled that an SC and 3.2 Carrera should be *that* different in weight. You need to input accurate data to get good results from the calculator. I didn't run or recheck your numbers so I can't comment on whether it's correct. Should be simple enough however. Just be accurate with the input numbers, and all should be fine.
If your car had Bilsteins before...and now have new Bilsteins..then you should be OK. If your car had hydraulic shocks before..and now you have Bilsteins..then I would target a new free-hanging droop angle that is 1 degree more horizontal than the calculator suggests...to compensate for the tendency for high-pressure gas shocks like Bilsteins to raise the car somewhat.
--Wil Ferch

Wil Ferch · 04-29-2003, 12:39 PM

OH...and you may want to adjust the two-piece spring plate to "mid-range"...so when you're all done, you have about a (+/-) 3/8" range of adjustment...for fine-tuning.
---Wil Ferch

widebody911 · widebody911's Garage

From what source did you get your weight figure? You should find out what the car really weighs. From my experience, the number shown in the door jamb and owners manual seems to be a bit on the heavy side, so your car will end up higher than you want.

kstylianos · 04-29-2003, 12:44 PM

Thanks Wil,

I had the standard Boge's before, thanks for the tip.

I'll use the 3.3" measurement and lookup the weight in the owners manual.

I should be good to go tonight.

-Charlie

kstylianos · 04-29-2003, 12:46 PM

Thom,

The car isnt at work so I used the Rennlist FAQ to find the weight.

ckelly · 04-29-2003, 01:45 PM

I just installed my 30's in the rear using this method. I used the weight published in the owners manual, plus myself, and some fuel. Spring angle came out to 21-22 degrees. I set the car on 4 jack stands, as level as I could using the door sill plate as a guide. Set the adj. bolts to midrange, and set the angle exactly at 21-22 degrees.

Worked perfect, right on the money, minor adjustments was all that was needed, no re-indexing......1st try.

widebody911 · widebody911's Garage

Ok, works for me. I actually went to the trouble of weighing mine.

kstylianos · 04-29-2003, 04:20 PM

Just recalculated with:

Weight = 2756-lb (Owners Manual)
Static Plate Droop = 3.3 (taking into account 24.5 desired ride height)
Rear torsion bar size = 28mm
Weight Distribution = 40/60

Calculated Angle = 22-23 degrees unsprung

Shooting for 21-22 degrees due to the gas Bilsteins.
Probably will go with 22

Thanks again guys.....

Won't know how it really turns out until the engine goes back in and the Bilsteins settle.

-Charlie

Wil Ferch · 04-30-2003, 12:54 PM

Let us know... Charlie....

Clay...it warms my heart to hear someone say it works the first time. That was the whole point of publishing this method in the first place, I was tired of hearing people say it may take 4-5 iterations to get right. All for a car platform that's been around for 30+ years..for goodness sake !!

---Wil Ferch

widebody911 · widebody911's Garage

Quote:

Originally posted by Wil Ferch
I was tired of hearing people say it may take 4-5 iterations to get right.

BTDT. I even broke my thumb dismembering a spring plate once.

Wil Ferch · 05-01-2003, 07:10 AM

Thom:
V. sorry to hear that...didn't know.

Pioneering has its drawbacks, eh?

---Wil

kstylianos · 05-01-2003, 07:22 AM

Installed the swing arms and indexed the t-bars last night.

The rake, depending on the side I was working on, was between 3.5-4 degrees (nose down). I subtracted this from my desired angle and was able to set the bars spot on. I'll let you know what height it eventually settles down to.

Used this tool from the Home Depot:

BGCarrera32 · 05-01-2003, 07:55 AM

So where does one find the calculator???

kstylianos · 05-01-2003, 08:01 AM

http://vintagebus.com/cgi-bin/spring.cgi

BGCarrera32 · 05-01-2003, 08:03 AM

Dunka.

Craig Roche · 03-29-2004, 07:33 AM

Charlie,

I was reading your thread and I'm curious to what your results were. I'm ready to install my springplates with Chucks bushings and revalved Bilstein Sports. Is it correct that if your cars sill is level then you just use the number the calculator gives, no adjustment? Did your allowance for the Bilsteins work out? Thanks!!