Ode to the Ferch Method

[cowtown]

I'm slowly learning about suspension setup. Working on the ride height on my '75 again tonight, I was running some numbers through Wil Ferch's height calculations, on paper and with Thom's calculator, and thinking about the reasoning behind his method. I just want to say, Wil has saved a lot of people a lot of time, and really given something to the DIY 911 crowd.

My car has 21/26 bars, and I was going for fender heights of 24.5" rear, 25" front.

With an estimated 40/60 split at 2300(car) + 200(driver) lbs, it predicted 26-27 degrees of droop. That gave a height about 5/16" too low...I think the actual distribution on my car with the 930 engine and FG front end is more like 35/65.

The magic number turned out to be 28.1 degrees for my situation. To be able to get that in three tries just seems like magic to me.

I can't imagine what it would be like to do this setup blind, without any up front math predictions.

Thanks Wil!!!

Now on to the corner balance and alignment!

[Pat S]

Sweet!,
I'll be doing this in a month or so on my 74 911 also with 21/26s but with a stock 2.7. Do you have the link to Wils formula?

Pat

[ubiquity0]

I think its on www.vintagebus.com, then there's a 'Porsche' link.

[Pat S]

Ahh,
I knew Thoms was there but never saw the other article behind it, thanks.

[Wil Ferch]

Gee ( blush)...thanks for the kind words:
Accurate input is critical to accurate output. Here's some more thoughts from a different thread on this subject. Note the weight affect of a 152 lb driver on the 4 wheels...you can proportion up/down from this "typical" driver weight too, if you wish.
Thanks...
---Wil

In my opinion, you have the option to add ( or not add) your weight. Remember, the calculator works best if you know the other variables rather well ( vehicle weight and individual wheel weights, for example), ...and most people take a "stab" at the vehicle weight and get close.

If you want to be real anal about it, you can:
-- add your weight...but you'd have to figure how much of this the rear of the car sees. For a 150-152 lb driver.... it affects the four corners of the car this way ( looking down on car):
+62 +11
+50 +28
.... so the rear of the car would ( in total) weigh 78 lbs more than thought...with 50 of that on the left-rear and 28 of that on the right-rear ( USA type seating...not UK).

--- and...you can fudge the numbers to account for the slight left-side bias these cars show..and set your spring angles for this slight variation, too. It depends how accurate you'd like to get... balanced against how "good" the more basic numbers are to begin with ( individual wheel weights).

---Wil Ferch

[tiorio]

(I thought the title of this thread was 'Ode the the FRENCH method'...so many quips had I, until I realized...drat! foiled again)

[cowtown]

LOL tiorio.

I stuck 4 bags of softener salt (200lbs total) in the drivers seat while I was doing all this. I knew there had to be some advantage to living in an area where the calcium clogs the pipes.

One issue I'm having now, even at 24.5" rear, 25" front, is there a three-finger space between the top of the tires to the fender lip.

The PO put 205/45-16 tires on the car. I'm going to measure just what the diameter on these things is when I get home. Probably way too small. (Edit again - tire calc. indicates diameter is 23.3", and stock is 24.9". So the tires are lowering the car an additional 0.8 inches )

The car looks like it's at USA height, even though it's not.

On the bright side, I can reindex the rear bars in an hour now. Practice makes perfect, I guess.

EDIT - PS Wll I think I see what you're saying about fudging the angles a bit for the left-to-right split. Fortunately, I have adjustable spring plates so I didn't bother. I matched up the angles from left to rigth.

I'm going to try to get the side-to-side levels perfect when I attack the car with my load checker.

[widebody911]

Here's the link to the spring plate calculator:
http://www.vintagebus.com/cgi-bin/spring.cgi

[vash]

thanks widebody, the math makes sense. i think it is Hooke's law with some trig. i am going to print it so i can read it later. cowtown, you can do it in an hour? i think i read the tech article several times and that took me an hour alone

[vash]

wil ferch, that is pretty slick. the "ferch" method it is!