964-C2

Thank you for your inputs and explainations Van!
I understand and agree with most of what you write, but I do not understand why you have to square the motion ratio to get the wheel rate. I think the wheel rate should be just (spring rate) * (motion rate)??

In this link it is not squared:
http://members.rennlist.org/dan10101/944SpringRates.htm

Van

I'm not telling you what to believe or think - I'm telling you what I believe and think.

I would just caution you, before you decide to believe that the motion ratio is not squared, do some research, then make an informed decision.

I don't know who Dan10101 is - and I mean him no disrespect - but here's the link to Wikipedia's page on suspension geometry which explains why the motion ratio is squared: http://en.wikipedia.org/wiki/Suspension_(vehicle)

And here's what Eibach, the spring manufacturer, has to say about squaring the motion ratio: http://www.eibach.com/eibach/img/ers...nworksheet.pdf

333pg333

Nice for some.

This is an ENZO for sure but it's in context here. This was some dialogue I had with Karl about my then incoming KW setup. I had been given some other numbers by a guy on another forum, Bob, which Karl disagreed with. The guy was saying that my setup couldn't possibly work so I asked Karl for some clarification. You can see that he uses the formula squared as well.


"Patrick,

I have not spoken with Bob, and actually don't know who he is. But believe
me, my numbers correct (or close to it - see the following explanation).
The info on Paragons site is stuff they got from me a few years ago. In any
case, the 47% is a number that I have calculated By taking measurements. I
am now pulling out one of Porsches own Motorsport sheets that shows all the
rates of their Turbo and "Cup" cars back when they ran competitively.
Porsche lists the 25.5 mm bar as 31 N/mm which is 177 lbs/in. They also
then give the variable rate coilover helper spring rates at 34-65 N/mm which
is 194 lb/in - 371 lb/in. They then give the total Rate at the wheel(T-bar
plus coilover) as 45.4 - 58.5. Back out the rate at the wheel due to
torsion bar which they list as 31 and you have 14.4 - 27.5 at the wheel due
to the coil over. So take your pick, 14.4 / 34 is approx 42% or 27.5/65 is
42%.

Bob is right about them being inboard but his numbers are off. Actually
they are correct I think in that the motion ratio is about 65% but when
calculating wheel rates from spring rates it is the motion ratio squared
that is used. So 0.65 ^2 is , guess what,... 42.25% which is the number
that Porsches own sheet claims as I outlined above. So your torsion bar is
177 at the wheel, and your helper spring rate is a 285 which is 119.7 lb/in
at the wheel. So working backwards 177 plus 119.7 is 296.7 pounds per inch
at the wheel. Divide this by .42 and that is you equivalent coilover, or
706 lb/in coilover (initially I had 661 lb/in which is attributable to my
measurement error - I had 47% and Porsche lists it at 42%).

So it may be a bit stiffer in the rear than I might run but with the ability
to tune sway bars etc... you should be Fine. Your setup is actually much
stiffer in the front than the Porsche cup setup which ran progressive front
springs (200 - 371 lb/in) with the rear setup I described above which is not
that far from what you have( yours is 296 at the wheel and theirs was 259 -
334 lbs/in at the wheel).

Hope this make sense, but believe me, what is above is 100% correct. I can
fax you the Porsche motorsport sheet if you think it will help."

Darwantae951

Van,

Thanks for all your explanations in this thread, as well as all the points everyone else are bringing to the table. I'm researching suspension and spring rates and guess what? Search worked!

951_RS

Really great topic