wjk_glynn

Hi folks,

I'm planning on removing the rear torsion bars and installing the A1 Koni Cup coil-over kit from Paragon with 968 M030 sway bars. I'm also going to run 8x16 and 9x16 D90 rims.

I'm thinking 300 lbs/in springs up front and I need to pick a matching rear coil-over spring rate.

Since 300 lbs/in front springs are typically matched with 29 mm torsion bars, I used Paragon's page on Rear Spring Rates vs. Effective Rates to calculate an equivalent rear coil-over rate... and 525 lbs/in is the closest match.

So I'm just curious to know if others have experience with 300F and 525R rates (without torsion bars) and what are your opinions?

Thanks.

Karl.

thirdgenbird

i have the kit sitting at home, jason at paragon recommended a 100lbs split front to rear

i did 400 front 500 rear. i hope i didnt make a mistake...

xsboost90

i have 450F and 525R and it has just a touch of oversteer that i can balance out by adjusting the coilovers and/or rear tires and pressures. I would think w/ 300 in the front there would be much more oversteer.

Potomac-Greg

That does look like too much of a spread. I'd go lower in the rear and use the adjustable rear sway (3 settings) to dial in the balance.

wjk_glynn

Very interesting feedback. I really appreciate it.

I'm some what stumped that the 300-front/29mm-rear rule-of-thumb doesn't translate to 300-front/525-rear per the "effective" spring rates on Paragon's tech site.

Karl.

76 911s

Interesting, I'm using 340F and 550R on KW V3's, and it feels great. I'm on R's, and 968 M030 sways if that makes any difference.

wjk_glynn

I ordered the kit today from Paragon along with Racer's Edge camber plates and Elephant Racing rear spring plate bushings - Yay!

Jason at Paragon helped me with the order. He was very helpful. He runs without torsion bars on his 944 and based on his guidance, I went with 300F/400R.

And the beauty of removing the torsion bars is that if the car ends up pushing a bit more than I like, it's an easy and inexpensive operation to replace the rear springs with something stiffer.

Karl.

Potomac-Greg

The Koni Cup kit looks great. And it's a good value. It wasn't available when I did my suspension and I went with Bilstein Escort Cup.

The Koni's have a spherical bearing rather than rubber bushings, eliminating one worry that I have. The folklore says that the rubber bushing (in the Bilstein) may not be suitable long-term to carry the rear suspension load. I say "folklore" because I have not heard of actual failures. I've got my coilovers in tandem with t-bars, but I would like to dump the t-bars eventually to get total ride height control. But I do worry about those rubber bushings.

Van

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



If you want MY opinion, I think you need MORE rear spring, not less.

Van

What do you consider a failure?

vt951

+1, except that "Wheel rate is equal to motion ratio squared, times SPRING rate."

Potomac-Greg

That right there would be a failure.

Were these run in place of t-bars? How many years/miles?

vt951

Paragon must be assuming a motion ratio of 0.75, because .75^2 = .56.

Apparently, there is evidence to suggest the Porsche would side with Van's equations: https://rennlist.com/forums/4093528-post26.html

Van

Doh!! Good catch.

Yes, those were run with coil overs in place of torsion bars. About 4 years on a track car - 1,500 miles per year.

thirdgenbird

my kit came today, i lied... i did 350 and 450