dillon410021

What are you running? I have 500lb one in the rear. What should i get up front to compensate?

Zeff

Look at paragon's tech session site. They have all the info you need for effective spring rates with and without t bars. Figure the fronts at .9 to. 93 effective.

TonyG

Are you running torsion bars?


TonyG

Voith

Would front 500 and rear 350 make a good combination? Torsion bars not removed..

dillon410021

I have no torsion bars

TonyG

300lbs in the front with your current 500lbs in the rear would be a good place to start.

TonyG

DDP

If you want something relatively stiff, 500 rear with no T bar is not enough. That's an effective of only 200 lbs. If you're thinking 300 front I would run no less than 650 rear.

Ski

dedicated track car, 650 in the front, 900 rear.

TonyG

So how did you come up with a 500lbs rear spring having a 200lbs effective rate?

TonyG

DDP

500 * (.40) = 198 ish

TonyG

Are you saying that .63 is the displacement ratio?



Tony

dillon410021

Yeah, please explain. This car will be a street/ track car. I just dont the *** to sag when i get into it or to have massive roll when turning. I am young so a rough ride doesn't matter.

TonyG

I was referring to the formula to get the effective wheel rate from the advertised spring rate. In other words... a 500lbs spring doesn't equate to 500lbs of spring at the wheel because of the fact that the spring isn't connected to the trailing arm at the axle center line. It's located inboard with creates a mechanical advantage.

That said, I just didn't agree with the formula used to indicate a 500lbs spring creates 198lbs at the wheel.

So if you have a 500lbs rear spring, and you want a starting point for the front spring rate, you need to know what the effective wheel spring rate will be for the 500lbs spring. Then you get something close to that for the front.

It's my understanding (and I personally have not taken the measurements of the control arm ... so I don't know this for a fact), is that the effective wheel rate is approximately 56%.

I have several control arms here. I should take the measurements and do the calc myself.

TonyG

kinglenario

Agreed. .56 is what I've always gone by in the rear.

But I found the post by Van which he stated this...

If you do the math, here's what you get:

Front motion ratio = 91%

Rear motion ratio = 63%

Wheel rate is equal to motion ratio squared, times spring rate.

For the front, that would be (0.91^2)*350 = 290 lbs/in

For the rear, (0.63^2)*525 = 208 lbs/in

DDP

Well, not correct is harsh. I can agree there may be different opinions on the subject. There are two different ways to figure spring rate, calculating and actually testing. And if you're calculating there are a lot of things to consider. I personally have not made any calculations on a car so my opinion is somewhat limited and I go by what other people have actually measured and how cars I set up feel. First off, ignore my .63^2 because that can get confusing and I just happen to remember it that way. .63^2 is roughly .40. So 40% of the spring rate is the effective wheel. On the old paragon tech, what most people used to go off of was .63. Well that site is quite old at this point and since there has been a few changes of opinion. From people who have actually calculated, they've figured from .4 to .45. At least from what I've seen. Apparently if you read the following thread, someone mentioned Porsche Motorsport tested it to be .42. I'm not sure how valid that is but it falls in line with everything else.

When I set up my first 944 forever ago, I used the old Paragon .63 and the rear was FAR too soft. The effective was most definitely not what I calculated.

Tony, which value do you use and what are your spring rates on your race car?

Dillon, this thread has everything you'll need:

https://rennlist.com/forums/944-turb...-enclosed.html

I would just suggest you don't go over 300 in front if you're driving it on the street. That's plenty stiff and the car will handle very well without knocking your teeth out. Tony has a good suggestion there.