Handling. Yet these boards seem to talk about everything but! How do you custom taylor the Oversteer/Understeer....What is it? What are you experiencing? How do you adjust it and to what degree?

 

Well, let me start this discuession off.

Understeer:
Push, plowing, front tires slide out first. Usually slight understeer is safer.

Oversteer:
Loose, rear tires slide out first. Oversteer can be dangerous, especially at high speeds.

Agree, disagree, want to add something.

 

There are volumes on this topic, of course. In order to know
what to do, or what is the cause, the context needs to be
known. Under/oversteer can be driver-provoked/caused,
and also conditions-caused. A car which is neutral at speed A
may be tail-happy (oversteer) at speed 2*A.
The critical information is found at the tire. Under the conditions
you want to stick, what are the tire temperatures? (inner,
middle, and outer portion)? First you should get the allignment
and tire pressures so that the temps are as even as possible
across the outside tires, *and* as hot as the tire manufacturer
says it should be for best performance. In autocross, for instance,
there are cases where folks go to narrower tires so they get
hot enough to stick, as opposed to wider tires that never get
warm enough! With our heavy car, the tires will get hot enough.
Once you've obtained that, and are driving smoothly enough to
get reproducible results, then you can alter your sway-bar
stiffness to make one end change. You loosen the sway bar on
the end you need to stick more, or alternatively tighten up the
end you want looser.
Joe

 

I burnt off a set of rears in my first season (outside 1/3 on both sides). I put on a new set of tires last fall and had the dealer apply as much negative camber as the stock (ROW) suspension would accept. My objective was to get more even wear on the rears by increasing the contact patch in cornerrs where the bulk of the wear occurs. I haven't tracked the car since (winter) but have concluded that I will be seeing a lot more understeer next spring as the rears stick better due to the increased contact area. Is this a correct assumption? If so, what's a simple fix without doing PSS9's? Can I simply put a stiffer rear sway bar on?

 

Joe,

Before I posted this topic I was betting the first responses would come from you and Cary. I am happy to say you didn't disappoint.

I would like to take this discuession into alot more detail. Take the tire pressures. If you want to correct for understeer you would raise the front tire pressures. If you wanted to correct for oversteer you would lower the front tire pressures. Correct?

To correct for understeer you could also lower the rear tire pressures. To correct for oversteer you would raise the rear tire pressures. Correct?

What can we do in addition to adjusting tire pressures to modify the handling characteristics?

 

How were your fronts wearing? If you had the tire temps, you'd
know whether you could use more negative camber there too.
Change one thing at a time. Wait till you see what the car does.
So how much negative camber do you have now?
Joe

 

Zippy,

If you want to correct for understeer in the front sway bar catagory, you would soften the front sway bar. If you want to correct for oversteer you would stiffen the front sway bar.


Addressing the rear sway bar, if you want to correct for understeer you would stiffen the rear sway bar. If you want to correct for oversteer then you would soften the rear sway bar.

Caution, work in small increments or changes. In addition work with one sway bar at a time.

 

Zippy,

Addressing the camber issue, to correct for understeer you would increase the front negative camber. To correct for oversteer, you would decrease the front negative camber.

 

What about shocks? Do they play a part in their adjustment for understeer/oversteer? Any thoughts? I have listened in amusement to discuessions stating "I run my PSS9's at number "X" in the front and "Y" in the rear." Does anyone care to comment why you adjust softer or stiffer versus front and rear? What is trying to be accomplished?

 

We all have the same 'hot buttons'...
Not exactly. If your rear tire is at 20psi and you have
understeer, you're not going to lower the rear pressures,
and if you have oversteer and you're already at 50psi, you're
not going higher.
You fundamentally have to know why your car is steering
the way it is, by examining the tire temperatures (and/or
wear if you drive the same way all the time). If a car's
camber is wrong, you may be understeering because the
fronts are riding on the edge of the tire. The temps/wear
will show that, and the solution would be to adjust the
camber. If both front tires were wearing/hot on the insides
you might have too much toe-in, which means the tires were
fighting against each other, and would cause understeer.
It the tire temp/wear is concentrated in the center of
the tire, then you would lower pressure. If it dips in the
middle, you would raise pressure. If it's too hot all over,
you need less weight distribution/transfer to that tire.
If it's too cold all over, you want more weight. The weight
is affected by roll-bar settings, spring rates etc. If you're
only turning one way like the good ol' boys in stock cars,
you can even put a mite-bigger diameter tire on one corner
to get more weight there. Just be careful turning the other
way though.
Joe

 

The fronts were worn a lot more evenly, but with a bias to the outer edge. Overall front tire wear was minimal enough to fascilitate a second set of rears.

I don't know what the actual amount of - camber is on the rears. Al I know is that it's at the limit of the stock (ROW) setup. By eyeballing it, it is visually noticeable, but only if you are looking for it. Is there a simple method of measuring this?

Mike

 

Joe,

Can't believe this conversation is limited to you, me and Zippy? Either everyone is set up perfectly or they don't care. Maybe Porsche isn't all about handling as everyone says.

Your point about temperature reading is well taken. Going to extremes on any item will not help to attain what you are looking to achieve. What I was hoping to convey was, many parameters are involved and it helps to know what you can do to achieve the desired result.

In addition, you have added toe in, spring rates and tire diameter. Let me first go back to the shocks. My understanding is, if you want to correct for understeer, you would soften the front shocks along with softening the bump. To correct for oversteer you would stiffen the front shocks. You can also correct for understeer by stiffening the rear shocks and correct for oversteer by softening the rear shocks.

 

Joe,

Addressing the toe in, it is again my understanding if you want to correct for understeer you can add more front toe out and/or reduce rear toe in slightly. To correct for oversteering you should add more toe in up front and/or increase the rear toe in.

Springs: To correct for understeer soften front springs and/or stiffen rear springs. To correct for oversteer, stiffen front springs and/or soften rear springs.

No wonder most people like engine modes better, they are simpler and easier to comprehend.

 

Opps, forgot to put my two cents in regarding tire diameter and width. Correct me if this is wrong, to correct for understeer you can decrease the front diameter, increase the rear diameter, widen the fronts and narrow the rears. To correct for oversteer you increase the front diameter, decrease the rear diameter, narrow the fronts and widen the rears.

It is important not to make big changes and then to change only one item at a time and test to see what was accomplished.

Any ideas as to what lowering the front or raising the rear does to oversteer/understeer?

 

Just got a reply. To correct for understeer you can lower the front and/or raise the rear. To correct for oversteer you raise the front and/or lower the rear.

Any ideas as to what widening the stance will do to understeer/oversteer, if anything at all?