Over-steer or Under-steer... that's the question...

[MNBoxster]

Originally Posted by John V

Jim, I'm not trying to be difficult, but it's really impossible to know just by looking at the suspension alignment settings how the car will behave. I'm sure the engineers did what all engineers do: they started with a baseline (based on past experience, computer modeling, etc) and then went out and did some testing. From there, I'm sure they tweaked spring rate, tire size, ride height, ARB thicknesses, damper valving, alignment, etc to acheive the balance of ride and handling (and within that, the balance of safety and tossability) they wanted. But no matter how smart you are and how much you know about suspensions, it's impossible to just look at all these pieces of hardware and tell ANYthing.

Someone always mentions the skidpad test. I think it's the most over-published figure of merit when talking about automotive performance. How often are you driving a Boxster around a perfectly flat piece of pavement in a 100' radius curve? Not very frequently. More often, if you're driving spiritedly, you're dancing the car through a series of switchbacks. Or you're driving on a country road with rolling hills and fast, sweeping corners. Either way, it's dynamic. You're on the throttle, on the brakes. The corner decreases or increases in radius.

Forget spirited driving for a moment and consider a complete non-enthusiast driving the car. In certain circumstances, the car's natural tendency is to understeer. In other circumstances, the car's natural tendency is to oversteer. In fact, in my opinion the car is set up to oversteer in a situation which your average driver could encounter - the typical USA freeway exit ramp - which is a decreasing-radius corner after a high-speed straightaway. Go into that corner too hot and drop the throttle and the back end will come out. Your average Honda, Toyota or even BMW won't do that. Of course I like this kind of behavior - it makes the car interesting to drive, and it gives the driver a bunch of options when it comes to driving quickly. But when it's raining outside and my girlfriend has borrowed the car? I'm not thinking about it being a steady-state understeerer, I'm thinking "what are the odds she's going to back it into a guardrail?" (Fortunately, she can drive).

I think this is an interesting discussion, one that comes up frequently in my circle of autocross and track fiend friends.

Hi,

Well you are being a little difficult. Nowhere did I say that the alignment specs alone dictated that the car over/understeers. But, in the case of the Boxster with + Camber in Front and - Camber in the Rear, coupled with the Tire size, width, inflation pressure, these do bias the car (any Car) toward understeer. Add the differing Tires widths, offsets, pressures (not to mention Anti-Roll Bars and differing Spring Rates F/R) and you have a car which absolutely understeers naturally - it simply MUST!

Also, you seem to be denying that a car even can be setup to favor one characteristic over another. This is just nonsense. Cars are setup to achieve a desired response on the road and manufacturers (and their Legal Depts.) always favor inputting understeer for safety and to make the car pleasurable to an average, or not so average, driver to drive. It's as much a Marketing thing as a Liability one, it gets the Secretaries to line up to buy one as well as the enthusiast. It makes the car easy to drive by most people's standards.

If the car is so setup, you must mitigate this natural tendency by altering the variables or driving style to negate or overcome these. You said earlier that a car cannot be setup neutrally and still be safe, but you fail to acknowledge that a car can and is setup to favor one characteristic over another. Everything else is just an Academic arguement which no one made, or disagrees with...

Happy Motoring!... Jim'99

[John V]

Originally Posted by MNBoxster

Hi,

Well you are being a little difficult. Nowhere did I say that the alignment specs alone dictated that the car over/understeers. But, in the case of the Boxster with + Camber in Front and - Camber in the Rear, coupled with the Tire size, width, inflation pressure, these do bias the car (any Car) toward understeer. Add the differing Tires widths, offsets, pressures (not to mention Anti-Roll Bars and differing Spring Rates F/R) and you have a car which absolutely understeers naturally - it simply MUST!

This is where I disagree. I can build you a car with positive camber up front and negative camber in the rear, wider tires in the rear, stiffer front springs and STILL make that car oversteer in a steady state. It's just not as simple as you're making it out to be.

I think you understand what I'm saying and I understand your overall point about having a car that will have the front end lose traction before the rear in a steady state around a constant-radius corner. I guess that just isn't very useful information to have.

[MNBoxster]

Originally Posted by John V

This is where I disagree. I can build you a car with positive camber up front and negative camber in the rear, wider tires in the rear, stiffer front springs and STILL make that car oversteer in a steady state. It's just not as simple as you're making it out to be.

I think you understand what I'm saying and I understand your overall point about having a car that will have the front end lose traction before the rear in a steady state around a constant-radius corner. I guess that just isn't very useful information to have.

Hi,

Again, you're delving into the realm of the Academic here. You may well be able to "build you a car with positive camber up front and negative camber in the rear, wider tires in the rear, stiffer front springs and STILL make that car oversteer in a steady state." I'm not disputing that. Nor do I dispute that there are greater complexities than those mentioned here.

But I don't believe that you can take a Boxster and "build a car with positive camber up front and negative camber in the rear, wider tires in the rear, stiffer front springs and STILL make that car oversteer in a steady state".

The Boxster naturally understeers. This has been both my experience, and many other members' experience. Virtually every Driver Review ever done on the car as well as the view of most Aftermarket Suspension tuners share the same view...

Happy Motoring!... Jim'99

[John V]

Maybe it's a difference between the S and non-S cars, who knows.

I'll happily drive my neutral car and you can happily drive your understeering car and that's just fine.

[z12358]

Just curious, what are the definitions for over/understeering?

Originally Posted by z12358

Just curious, what are the definitions for over/understeering?

Good question, Z! I have used this a few times to educate myself on this topic:

http://en.wikipedia.org/wiki/Oversteer

[GmanMD]

Just thought the following would be interesting to read. It's from Wikipedia:

A car that tends neither to oversteer nor understeer when pushed to the limit is said to have neutral handling. It seems intuitive that race drivers would prefer a slight oversteer condition to rotate the car around a corner, but this isn't usually the case for two reasons. Accelerating early as the car passes the apex of a corner allows it to gain extra speed down the following straight. The driver who accelerates sooner and/or harder has a large advantage. The rear tires need some excess traction to accelerate the car in this critical phase of the corner, while the front tires can devote all their traction to turning. So the car must be set up with a slight understeer or "tight" tendency. Also, an oversteering car tends to be twitchy and ill tempered, making a race car driver more likely to lose control during a long race or when reacting to sudden situations in traffic.

Carroll Smith, in his book "Drive to Win", provides a detailed explanation of why a fast race car must have a bit of understeer. Note that this applies only to pavement racing. Dirt racing is a different matter.

Even so, some successful race car drivers do prefer a bit of oversteer in their cars, preferring a car which is less sedate and more willing to turn into corners (or inside their opponents). It should be noted that the judgement of a car's handling balance is not an objective one. Driving style is a major factor in the apparent balance of a car. This is why two drivers with identical cars on the same race team often run with rather different balance settings from each other. And both may call the balance of their cars 'neutral'.

The full explanation of oversteer/understeer is here: http://en.wikipedia.org/wiki/Oversteer

[z12358]

From the wikipedia article (which was written by who knows who):
"To put things in even simpler terms, when you turn into a corner, oversteer is when the car turns more than you expected and understeer is when it turns less than you expect."

Seems to me one cannot objectively define "overX" and "underX" without objectively defining "X" first -- and X here is "steering". When does the car turn more than you expect? And can different people have different expectations? Is it oversteer if you already expect it?

I know very little on this subject but I liked the 987S MUCH more than the 997 I tested. Much more neutral and controllable.

[Topless]

Originally Posted by GmanMD

Just thought the following would be interesting to read. It's from Wikipedia:
It should be noted that the judgement of a car's handling balance is not an objective one. Driving style is a major factor in the apparent balance of a car. This is why two drivers with identical cars on the same race team often run with rather different balance settings from each other. And both may call the balance of their cars 'neutral'.[/I]

The full explanation of oversteer/understeer is here: http://en.wikipedia.org/wiki/Oversteer

This is so true. How different drivers set up for a corner greatly affects perceived car balance and handling. This is why every car that is driven to the limits of traction should be set up for driver style and preference. John and Jim might (and probably would) drive the same car and one would notice distinct understeer, the other would find the car very neutral to his driving style. Care to guess which one is which??