I'm looking for some opinions.

I'm currently running 300# front springs on rebuilt and revalved Koni yellow M030 struts in the front, and 28mm torsion bars w/ new Koni yellows in the rear. Suspension upgrades also include Weltmeister swaybars, Racer's Edge camber plates, geometry-correction balljoints, 968 caster blocks, delrin spring plate bushings and an upper strut tie bar.

The handling on street and track is good. However, it does tend to understeer, even with swaybars adjusted to compensate (front set almost full soft, rear almost full stiff). The understeer is most evident in slow corners, and is pretty bad in autocross. On the track it's safe and can be dealt with effectively by throttle steering. Front tires still wear slightly quicker than rears.

After doing some research, I've decided that 29mm torsion bars would have been better suited to my 300# springs than the 28mm bar that I'm running. The ride quality on the street is absolutely fine, so I'm considering going stiffer.

This is where I'm looking for opinions from those of you who own or have driven such setups. I'm interested in either 350# front springs with 30mm torsion bars, or 400# springs with 31mm torsion bars. Car is still driven on the street, and I'm not interested in a brutal ride and bent rims from the occasional pothole. I'm looking for what most of us high-performance enthusiasts would consider acceptable / tolerable ride quality on the street. I'm sure both options will be excellent on the track, since my 300/28 setup is already quite good. The delrin spring plate bushings were recommended to me by Paragon as *must-haves*. What would be the next most important front and/or rear end bushings that I should consider swapping to solid?

Thanks,
Ian

 

Hey Ian
I am running a very similar setup (see below) I went 325#/29MM bars - is nice balance
definately streetable and well mannered all around

Koni struts and shocks (M030 optioned and turboS cars)
Front springs: 2.5” spring conversion with 10” 325# hypercoil & racers edge perches
Rear torsion bars: 29mm solid weltmeister performance
Rear spring plate bushings - poly-graphite inner and outer: weltmeister performance
19mm Geometry Correction Kit Ball joint kit – Renbay solid bushing, chromolly ball pins
Spindles machined for 19mm ball joint pins
Front Sway bar – Porsche 968 mo30 30mm frnt sway, mounts,bushings + KLA supports
Rear sway bar - weltmeiser 22mm fully adjustable rear sway bar, end links with rod ends
strut mounts upper – late M030 (improved from 86 design)
KLA strut tower brace
Corner balanced

 

im running 400's up front and its perfectly drivable for me at least- w/ 18's around town.

 

I'm running 375# up front 475# rear. Car very neutral on track.
On the street with 18" wheels it's fine except on really
bad roads, but I try to stay off those.

 

I'm running 350#/30mm bars and it's very neutral at the track... at least enough that I have my choice of oversteer or understeer based on sway bar settings. At my last autocross I was within a few tenths of the quickest 'car', and only about two seconds from FTD... a national-runner-up driver in a Forumla 500.

That said... I'm contemplating going stiffer front & rear. I find that if I set my sway bars any stiffer than 50% I get too much inside wheel lift... any softer and I quickly get a lot of body roll.

Worth noting though... I'm pretty sure my car is a little 'nose heavy' right now, as I think I've removed more weight from the rear than the front right now. Also my rear ride height is about 1/2" higher than the front.

 

Here's a picture of the body roll with 350/30 with front bar set to ~50% and rear to about 25% stiff.

 

Sounds like 400# / 31mm torsion bars may be where I'm headed. Thanks guys.

 

Where are you planning on getting 31mm torsion bars? (not hollow) I didn't know they were available for our cars at least not anymore.

 

According to Jason @ Paragon, the 31mm torsion bars are only available in hollow. As I understand it, these are 31mm effective.

 

I think the 31mm hollow bars are actually 30mm effective but I could be wrong.

 

You're understeering because you're on your bump stops because of too soft of a front spring rate. I would run 29mm bars with 400# or >450# with the 30mm bars.

 

Also - what is the rest of your setup:

- Tire size and type (street or R comp)?
- Alignment specs?
- Shocks settings?

 

I'd say that to get rid of the understeer you need t-bars rated 1.25-1.4 x front wheel rate ( of the spring, of course ) . So if running a 400lb/in springs at front you'll need t-bars of ( 400 x 0.9 )x 1.25 - 1.4 = 350-500 lb/in.
And, according to http://www.tech-session.com/kb/index.php?article=39 31mm t-bar has wheel ( = efective ) rate of 382 lb/in, 32mm = 434lb/in and 33mm = 490lb/in

 

Does anyone know if you can (still?) buy 31+ mm torsion bars for our cars? I know they make them for 911's...

 

Skip -
I'm running Toyo RA1's, 225-50/16 and 245-45/16, alignment settings are 1.5 degrees neg. camber front, about 1.3 degrees rear, max caster front, slight toe-in front and rear. I was thinking about 2 degrees negative camber front and rear for my next alignment. Front and rear Konis set to 75% rebound damping.

I'm glad I posted this topic. Skip - I thought I had this all figured out! I suppose it's possible that I'm hitting the bump stops, it would only take a couple inches of travel for that to happen. I'll have to check the bump stops and see if there are any signs there. I dunno though, if that's what it is, why would softening my front swaybar and stiffening the rear bar help? And my track photos don't show excessive body roll.

What front spring would you recommend with my existing 28mm torsion bar?