CO951

I have an '89 951 with the 968 MO30 swaybars. The rear sway is set at the stiffest settings and has the non-rubber rear drop-links. I then replaced the inner rubber bushing on the front bar with delrin bushings and installed a racing dynamics strut brace. After the change I have noticed a very clear increase in OVERstear in my last three track days. From what I understand both the strut brace and the delrin bushing on the front sway should increase UNDERsteer. Any ideas on why I'm getting the oppisite effect, or and I just confussed?

pontifex4

When are you experiencing this? Corner entry / mid-corner / corner exit?

The front upper strut brace's job is primarily to prevent excess camber change on the front wheels. In practice, this means that your outer front wheel will have more grip, and be more sensitive to corrections. Could that be what you're experiencing?

mj951

The oversteer is due to the short setting on the rear swaybar. There are a few other things in play but generally I have the same suspension mods as you on my '89 turbo and you should find the middle setting on the rear sway will be more neutral if not a little on the side of understeer.

CO951

Sorry if I wasn't clear, I didn't have the oversteer problems before the bushing and strut brace change.

The slower the corner, the earlier I have noticed the oversteer. In the slowest/hairpin corner I notice it on turn in and like it, but at corner exit I can no longer apply full throtle. Other corners I only notice it on exit.
I don't think it is just more sensitive to corrections, because I notice it places I'm not really making corrections. Although I've had to start making corrections because of it. However, if it increases traction in the outer front wheel, isn't that basically the same as saying it increases oversteer?

ZR8ED

Don't think of the strut bar as stiffening the suspension, but actually KEEPING the suspension working properly. Ie. The body is deflecting slightly during corning (flexing slightly)
You have effectively stiffened the chassis, which keeps the suspension operating as it supposed to. You are now increasing grip in the front end. You have not changed anything in the rear to increase grip, so it is like you have made the rear of the car MORE prone to oversteer than before.
Cause and effect. Changing the front suspension does more than just affect the front suspension characteristics.

Oddjob

What are you running for tires/pressures. Street tires, R-comps? Wheel/tire widths? Any changes to that setup between track events?

Alignment settings, camber and toe?

Stock M030 suspension, other than the 968 M030 sway bars? Do you know what your shock settings are at front and rear?

What track and what kind of lap times are you running?

A stock Turbo S with 968 M030 bars should not have much tendancy to oversteer, with or without a strut tower bar. Any chance that something is binding after installing the solid bushings?

teamking

You are confussed. ZR8ED has it right-- improving the front of the car has meant the rear is the lesser of the two, i.e. oversteer.

But, I think it's good news that you got noticeable improvement based on bushings and a strut bar. Now get to work on the rear suspension!

CO951

Thanks for straightening me out.
Oddjob- I have street tires in the stock sizes 225 & 245 on stock wheels. I don't have the exact allignment settings, but it is aggresive negative camber for a street car, but not for a race care. I haven't tuched the rear shocks and they are showing signs of some leaking. The front shocks are dialed pretty stiff, but are original and the setting wasn't changed. The solid bushings do make some noise when I do something that causes the bar to move in the bushings, so it is possible they are binding. For example under bracking when the nose dives the bar isn't twisting, but it is turning in the mounts and it makes a nocking sound. What could cause binding?

RedDragon

If you soften your swaybar a hole you will have less oversteer. Taking a few psi out of the rear tires will also help. Google "Rex on rails" for a great series of articles on how swaybars, tire pressure, ride height and other factors change a cars weight shift handling.

CO951

See this is where the confussion comes from, some people are saying the opposite of others. I am not asking how to correct the oversteer, just why it is happening. I was basing my understanding on tables like this one http://www.nyracer.com/overunder.htm
I have seen the same basic table in many different places, including a card my local Porsche shop gave me. The bushings would stiffen the front bar, which according to this info should decrease oversteer.
So the question is what does the strut brace do? The things that stiffen the front decrease oversteer. If the strut brace stiffens the front I would think it would lead to understeer.
Oddjob, what were your thoughts on how binding bushings could cause oversteer. What could cause binding?