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

[John V]

Originally Posted by MNBoxster

The Boxster uses a larger Rear tire than Front as an OEM spec., this will create understeer. Higher Tire pressures in the Rear than the Front, again OEM spec and inducing understeer. It uses a smaller Anti-Roll bar in OEM spec than say the M030 suspension, again favoring understeer. Chassis Ride Height is higher in the stock setup than say the M030 one, again creating a higher CGH and thus greater understeer.

I think you need to come drive my car, Jim. No understeer here. Maybe I got a "magic" one! Come to think of it, two of my buddies have (nearly identical) '03 3.2L cars, and neither of theirs understeers either.

Oh well, no worries.

[z12358]

Mine just goes where I point it. No over, no under, just perfect.
That is, when it's not stored for the winter.

[Sammy]

Originally Posted by John V

I think you need to come drive my car, Jim. No understeer here. Maybe I got a "magic" one! Come to think of it, two of my buddies have (nearly identical) '03 3.2L cars, and neither of theirs understeers either.

Oh well, no worries.

Try taking the car to a skid pad and see what happens...

[John V]

Originally Posted by Sammy

Try taking the car to a skid pad and see what happens...

I can go around a skidpad in steady-state understeer or steady-state oversteer. Does that mean the car oversteers AND understeers?

The point I'm trying to make is that there is a lot more to it than saying "this car understeers" or "this car oversteers." What are you doing when it over/understeers? Braking and turning into a curve? Going through the middle of the curve? Accelerating out of the curve? Going in a bit hot and decelerating / braking IN the curve? It's not as simple as people are making it out to be. With the Boxster (and several other cars I've been lucky enough to drive hard) you have so much control over what the car is doing, it's hard to just label the car as one thing or another.

[Sammy]

Originally Posted by John V

I can go around a skidpad in steady-state understeer or steady-state oversteer. Does that mean the car oversteers AND understeers?

The point I'm trying to make is that there is a lot more to it than saying "this car understeers" or "this car oversteers." What are you doing when it over/understeers? Braking and turning into a curve? Going through the middle of the curve? Accelerating out of the curve? Going in a bit hot and decelerating / braking IN the curve? It's not as simple as people are making it out to be. With the Boxster (and several other cars I've been lucky enough to drive hard) you have so much control over what the car is doing, it's hard to just label the car as one thing or another.

I'm with you John V in that what you feel on a track is dependent on what you are doing with the car; however, if you are doing a skid pad test correctly you will find one or the other. In every case I have driven a production level car on an actual skid pad I have found understeer.

[John V]

Originally Posted by Sammy

I'm with you John V in that what you feel on a track is dependent on what you are doing with the car; however, if you are doing a skid pad test correctly you will find one or the other. In every case I have driven a production level car on an actual skid pad I have found understeer.

Sounds like a meaningless test, then.

[Sammy]

Originally Posted by John V

Sounds like a meaningless test, then.

Not exactly as you gain knowledge into the roadholding ability as well as proof that the suspension set up works as its designed/supposed to by understeering.

For us normal people it is probably a relatively meaningless other than we can see that a Boxster will be able to hold the road better than a Geo Metro...

[MNBoxster]

Originally Posted by John V

I can go around a skidpad in steady-state understeer or steady-state oversteer. Does that mean the car oversteers AND understeers?

The point I'm trying to make is that there is a lot more to it than saying "this car understeers" or "this car oversteers." What are you doing when it over/understeers? Braking and turning into a curve? Going through the middle of the curve? Accelerating out of the curve? Going in a bit hot and decelerating / braking IN the curve? It's not as simple as people are making it out to be. With the Boxster (and several other cars I've been lucky enough to drive hard) you have so much control over what the car is doing, it's hard to just label the car as one thing or another.

Hi,

You have made your point and no one disagrees with you at all. A Driver can, through the modulation of Throttle and Brakes change the dynamics of the car.

But the Boxster, or any other car can be setup to favor either understeer or oversteer. As is the case with virtually all street cars, the Boxster is setup (through the selection of Tires, Tire Pressures, Spring Rates, Anit-Roll Bar Thickness and deflection, all Alignment Settings, etc.) to understeer - period.

You can go on and on about how this effect can be mediated by the driver, but two points need be added. A driver must be experienced and knowledgeable in order to be able to overcome the car's natural tendency (as setup) in a controlled way, as you predict. Most drivers are so experienced or knowledgeable, nor does the manufacturer make any such assumption that they are. So an inherent amount of understeer is dialed-into the car to begin with. And, if an average driver takes the wheel, his control inputs will generally cause the car to understeer as was the Manufacturer's intent.

If you understand suspension setups as much as you appear to, just looking at the OEM suspension alignment settings will prove to you that what I'm saying is correct...

Happy Motoring!... Jim'99

[John V]

Originally Posted by MNBoxster

If you understand suspension setups as much as you appear to, just looking at the OEM suspension alignment settings will prove to you that what I'm saying is correct...

Happy Motoring!... Jim'99

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.

[Topless]

As usual, you guys are both right. My car probably rolled off the lot with very slight tendancy to understeer. This is easily overcome with a little driver dynamics. Over time I have fine tuned my car to my driving style with different tire sizes, tire pressures and alignment, suspension is stock. It is now neutral and balanced to my driving style, maybe not so for someone else.

[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.