odurandina

i've read the posts but i am still a dumbass about suspension... but i'm hooked on the arms race modus.

i am running 18x8.5 255-35-18 front, 18x10 275-35-18 rear.


q1. i have 928 GTS big brakes on non M030 spindles with the use of an adaptor kit... once adding this kit and the sway bars, would i now, in effect, be running M030 suspension despite not running M030 spindles ?

q2. what spring rate would i want to have a stiffer but streetable suspension such that i could lower my front suspension, thus geting my front tires to tuck in closer into the fenders without problems. going 300 same as karl will work ?

q3. what spring rate would i want for the rears to accomplish the same. the 400 ?

q4. are these all height adjustable ?

q5. i've heard the stock suspension is the best for the street. my biggest concern is lowering my front wheels since my rear wheels are already resting at a perfect hight.


what should i do ? any ideas would be greatly appreciated.

mattipuh

there has been quite alot of discussion.
quoting van's one message, getting a good balange, you need to get spring motion ratios squared close to each other. Havin' bit stiffer motion ratio^2 front keeps car little understeery -> easier to handle with help of accelerator.

I planned to go F450 and R700. how harsh can you go depends also on the shocks you will use, and what comfort level do you require.
actually, now when calculating this, would F400 R800 be better split, which would give
Wheel rations (400/800)
Front 331,24
Rear 317,52
Seems to be ok, still softer rear -> not too tricky?

Wheel ratios (450/700)
Front 372,65
Rear 277,83
This feels understeery, already on paper... ?




Van's calculations

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


some topics disussing this
https://rennlist.com/forums/924-931-...-a-budget.html

https://rennlist.com/forums/924-931-...300f-525r.html

https://rennlist.com/forums/924-931-...treet-use.html

https://rennlist.com/forums/924-931-...oil-overs.html

https://rennlist.com/forums/924-931-...treetable.html

https://rennlist.com/forums/924-931-...questions.html

wjk_glynn

A friend and I ran the car at a PCA autocross event in November.

First, here's a clip of him driving the car:

http://www.youtube.com/watch?v=cr74878W_10

Next are shots showing maximum roll. Note that this was on Toyo R888s on grippy concrete.





So as you can see, there's still pleanty of roll with the setup.

Karl.

Eric_Oz_S2

Karl,

I have these shocks on the back with tbars and 250 helper springs, so maybe slightly stiffer than your 400# springs without tbar. I have mine set to 50% (options are only 0, 25, 50 and 100), so I guess by 75% (on your original setting) your mechanic means the third setting which is actually 50%.

Did you find the rear wants to hop around a bit over undulations? Mine seems to get into a bit of a bobbing motion on the street, but is great on a smooth track. On one particular track there are some ripples in the asphalt and it bounces enough so my helmet hits the roof a couple of times. I originally had them set to 25% but the rebound over large bumps didn't seem to be effectively controlled.

You mentioned squat issues. I don't see how the shock setting would effect squat as the compression stroke is not adjustable.

Did you notice much difference from increasing from 50 to 100% in terms of a) ride on the street; and (b) performance on the track?

PS FWIW I'm running Koni sports with the ARHK and 350 springs in the front - though it seems more settled than the rear.

wjk_glynn

Not so much.

As regards the street, it feels a bit more "jittery" in the back. Like high frequency motions were being passed through.

Track time has all been on the stiffer setting and it feels very good.

Karl.

Eric_Oz_S2

Out of interest, on what setting do you run the rear sway?

wjk_glynn

Middle setting.

Karl.

wjk_glynn

Hi folks,

So I've run some more track days with these and I thought I'd give an update on my impressions...

Several years ago, I once drove a (Powerhaus built) 3.0L turbo 968 that had custom modified 968 M030 struts/coilovers. I didn't record the spring-rates or valving, but I do remember the "iron control" that suspension had driving up and down Hwy-35 in the SF Bay Area (locals will know that road...).

It was brilliant.

This Koni Cup Kit with 300F/400R (torsion-delete) doesn't seem to achieve that same level of damping control.

It's good... but there's a bit of me that knows better is possible even with Koni products.

Some notes:

• The jittery ride (i.e. high-freguency bumps) remains, and sometimes (oddly) combined with a sorta slight bit of float/wallow on the highway if the expansion joints are a certain distance apart.
• If anything, the 300F/400R rates now feel a bit 'soft' -- maybe could do with a bit more rebound control(?)
• Feels very good at the track, very stable. But tracks are also very smooth and I'm still very much a novice at track events (usually run in 'B' group), so not pushing anywhere near as hard as others out there.
• I'm also finding the stock seats are not holding me in place anymore.

For the record, the following is what is installed:

Koni "Cup Kit" from Paragon Products, which came with:
- Koni front shocks (8641-1414S)
- Hypercoil 2.5" 300# front springs
- Adjustable ride height kit
- Koni 30-series rear coilover kit
- Hypercoil 2.25" 400# rear springs
- Racer's Edge Rear Shock Mounts
Elephant Racing rear PolyBronze spring plate bearings
Racer's Edge Camber Plates
Porsche front control arms refresh:
- Left control arm (944-341-027-02)
- Right control arm (944-341-028-02)
Porsche front caster block (951-341-023-01)
- Caster eccentric (951-341-431-02)
- Locking nut (900-910-115-02)
Porsche 30-mm front sway bar (944-343-706-30)
- Front inner bushings (951-343-794-05)
- Front outer bushings (951-343-793-31)
- Front drop-link donut bushings (951-343-795-01)
- Front sway bar end circlip (N-012-449-1)
Porsche 19-mm 3-way adjustable rear sway bar (944-333-701-01)
- Rear sway bar bushing (964-333-792-00)

I've a KLA strut brace that I'll have installed in the next few weeks...

Wheels
- Front: 8x16 D90 cast rims, Toyo R888 225/50-16
- Rear: 9x16 D90 cast rims, Toyo R888 245/45-16

Alignment
Front
- Camber: -2.5°
- Caster: 3.8°
- Total Toe: 0.10°
Rear
- Camber: -2.5°
- Total Toe: 0.14°
- Thrust Angle: 0.00°

And here's my 'Captain-Slow' impression: http://youtu.be/CVT9bcddkGw

Karl.

majsc

Thanks for the update......

Eric_Oz_S2

I have almost the same setup, but 350F and 225R + TBars. Same observations as you about lack of control on the road. Great on the track but not so great on the road. Seems hard over small bumps and not enough control over dips and large bumps.

wjk_glynn

Succinctly said.

Back in 2010, you'd commented:

I've the same experience.

Also, I sometimes get the impression that the front takes-a-set a hair's breadth faster than the rear.

Have you ever felt that?

Also, have do you get much squat under full acceleration (pre-SC install)? I get enough to notice, but not bad by any means (subjectively).

Thanks.

Karl.

Eric_Oz_S2

It seems that it takes about 20mm of movement in the rear before it starts to resist. Under acceleration there is a little bit of aquat still - nowhere near as bad as the stock suspension though.

All I can say is the setup doesn't inspire a lot of confidence on the street, although on the track it is actually quite predictable. I have spun it on the street at low speed while cornering in conjunction with a camber change.

KW Clubsport will be the next upgrade for me

wjk_glynn

Are you thinking V3 or the Club Sports?

Karl.

Eric_Oz_S2

The clubsports. They run a 540F spring which should be a reasonable compromise given that I only drive it to the track and the ocassional weekend blast.

wjk_glynn

I know the V3s have rubber bushings in the rear coilovers. Are the Clubsports the same?

As regards myself, I'm going to stick with the Koni Cup Kit for the time being for two reasons:

1) While not perfect over dips and large bumps, I don't find it egregious and it's certainly vastly better than the tired old stock setup.

2) To be honest, I'm not keen to put a lot more money into this car and I'd prefer to see if I can tweak my way to more optimal behavior (spring change maybe?).

I'm inclined to start a thread up on the Racing & Drivers Ed Forum to ask for advice...

Karl.