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

Please excuse me if this has been debated here before (or if this is an issue that everyone knows except me), but how would you closest describe the Boxster's handling -- does it under-steer, or over-steer?

Don't smack me for asking this -- as you can see, I intentionally left out 'neutral' -- meaning that I'm curious what you think the Boxster's handling leans to the most.

-- peer

Hi,

The Boxster, like most manufactured Street Cars, has some understeer built in. This is safer for the general public than either a neutral or oversteering setup.

But, this can be a complex set-up. The car can be changed somewhat just by differing tire pressure or tire size. It's one of the reasons the rear tires are larger than the fronts. A Neutral setup on the Boxster will be a handful for the unintiated or inexperienced driver - a lot less forgiving. Hope this helps...

Happy Motoring!... Jim'99

I would agree that the street set-up leans towards understeer.

At autocrosses I like to play with the pressures and get a slight bit of oversteer (usually means pumping the front up to equal the rear). I find the feedback to be easier to deal with when pushing the car around corners.

Just curious, since I've never driven an Audi TT 4wd, I wonder if the boxster under-steer less or more than the 4wd TT.

-- peer

2nd that about playing with the suspension setup. When I added the M030 Sway bars that I found really cheap on ebay, the ratio of front to rear stiffness moves the car away from understeering...........after I put em on, I went for a test drive and got rather...uh.....sideways....at the left turn exiting my housing tract......lucky for me I was able to hold it (barely) and not kiss a big ole light pole.

I've yet to experience true honest to goodness oversteer in this car.
My last car on Falken Azenis had PLENTY of tail happy traits.
BoxsterS may be the most boringly predictable car I have ever driven.
Turn wheel 15 degrees car turns 15 degrees.

Depends on your driving style. Like most mid-engined cars, if you transfer weight to the front (by braking) before a turn and then trail the brakes off after turn-in, the rear end will rotate very nicely. Get on the power too abruptly and you'll be sideways before you know it. Get it right, and you can acheive a pretty nice slip angle with all four tires.

If you just charge hard into a corner without slowing down, sure, the car will understeer. Through transitions (like a slalom) the back end will stay pretty planted if you are on the power. Start lifting off the throttle and the car can get loose in a hurry.

It really comes down to the driver, but the car does not have what I would describe as a lot of built-in understeer.

Wow, a great summary John. I just learned an awful lot. Thanks.

The Boxter is such a balanced car that significant understeer/oversteer should never be a problem. Weight the nose... get a little oversteer, weight the tail... a little understeer. If you are wrestling with your car over this it's probably time to fix the nut behind the steering wheel.

HI,

Both Topless and John V, while spot on, are describing the means with which to over come Understeer. But the Car, as set-up by the Factory, does have an inherent understeer.

The two most important factors that influence understeer and oversteer are Weight Distribution of the car and Roll Resistance which is varyable by selective spring rates. Having a basic design influence on these factors are front and rear Roll Center locations and Center of Gravity location (the height of the CG, or CGH) .

All factors affecting the car's handling act through the tires to the road surface. The most important tire characteristic is its development of a Slip Angle when lateral force (or accelerations) are applied. All pneumatic tires deform while cornering to some degree. They will follow a path between the steered angle and straight ahead.

Slip Angle is the difference between the line the tires are steered on and the line they actually follow. Slip angle is actually a drift angle. The angle of tire slip can depend on speed, lateral acceleration, vertical load on tire, coefficient of friction of the rubber, and tire pressure.

If the outside rear tire has a larger Slip Angle than the front outside tire, the car will oversteer. If the outside front tire has larger Slip Angle than the rear tire, it will exhibit understeer.

For example, a front heavy car will oversteer because the outside tire on the front will require a larger slip angle to handle the heaveir weight loading. Increasing the roll stiffness (with stiffer spring rates) on one end of a vehicle will yield a large Slip Angle on that end of the car. If the Roll Center is raised on one end, it will increase the load transfer and thus the Slip Angle at that end of the car. Varying tire pressure will also vary the Slip Angle. Lowering tire pressure will lower the load carrying capacity of a tire, so slip angle will be increased, conversely increasing the pressure will have the opposite effect.

Happy Motoring!... Jim'99

Jim you always have to think in terms of dynamics and weight transfer. When driving spiritedly, you're always either braking into a turn or accelerating out of it. The overall balance of the car determines how it handles this combination of inputs.

If one were to create a car which was perfectly neutral during steady-state cornering, it would be so loose as to be dangerous. Nobody would even want to race such a car because it would be so difficult to drive.

So overall, I disagree in that I don't think the Boxster really has any inherent built-in understeer. More frequently, the driver does.

If my car exhibits any specific characteristic, I'd say it is more on the over steer side. Do you think this is due to my 19" tires? Front strut brace? Tire pressures? Driving style...or lack there of?

All of the above can affect oversteer. Just curious... why the front strut brace? The 987S is an amazingly well balanced car right off the lot. There are a couple of guys around here who in stock trim regularly outrun all but the GT3's in the cones. On a tight course the 987S is near perfect.

Hi,

Well of course I think in terms of Dynamics. Oversteer/Understeer is a dynamic phenomena, you cannot have it if the car is static.

But, you can have the car statically setup to produce either condition by the selection of Spring Rates, Tire sizes and pressures, Anti-Roll Bar size and deflection, etc.

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.

It doesn't matter that you think or feel the car doesn't understeer, it does, it must, that's the way it was set up. Chassis Dynamics is a well understood science with predictable results. The US Market suspension settings, in fact, including those of the Sport Pkg., favor understeer much more than those of the ROW and ROW Sport Pkg. models do, just look at the differences in the alignment specs.

I'm not saying you cannot defeat or overcome this tendency toward understeer by changing some of the variables, or by driving style. What I am saying is that if you don't, the car will understeer...

Happy Motoring!... Jim'99

Hi Topless, I did it, just to do it. No real reason. It was a $350 gift to myself. And, a few guys on the Forum spoke about the added benefit to our cars.

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.

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

As you may have guessed from my signature I am somewhat of a purist regarding Porsche performance. I am a firm believer in "If it ain't broke don't fix it." regarding these cars. They really got so many things right the first time. I am also keenly aware that I am in the minority on this board.

From this perspective If I were in your shoes I'd: Restore it to stock setup, and get to a track with someone who really knows how to drive these cars. I'd spend some time on a skidpad first and discover my traction limits and characteristics. I'd practice creating and correcting understeer/oversteer until I really understood its causes and cures. Then I would begin to work the course. Nice cleanly carved carousel turns or am I pushing and sliding... balanced planted slaloms or wild unsettled cone bowling... gentle controlable 4 wheel drift in off camber turns or dangerous fishtails and spins.

After spending some quality time with the car a picture should begin to emerge in the relationship between car and driver. Now I am in a much better position to decide if changes to the suspension and setup are in order. Maybe different tire pressures, maybe more neg. camber, maybe I do need that heavier sway bar up front. Now I have a really good baseline to work from, I really understand the car and how these changes will affect its handling on my way towards my ideal setup.

These cars roll off the lot far more capable than most of us will ever be as drivers. What I am suggesting is that by modifying the driver first, much greater performance gains are to be had than by attempting to modify the car blindly.

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.

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. :)

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

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.

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.

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

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... :)

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

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. :D

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

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

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.

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?? ;)

Hi,

Sorry, but this is not true. Understeer and Oversteer are not nearly as subjective as some here are trying to make it. These are very definite, measurable phenomena.

The definition can be quite simple - Oversteer, the Car steers deeper into a turn than the turn of the steering wheel would indicate and the Rear End will break away 1st, with Understeer the Car turns shallower than the steering wheel would indicate and the Front End will lose traction before the Rear.

But, the reason(s) this occurs are very complex and a combination of many factors from Track (F/R), Tire size and pressure (even Tire Temp), suspension deflection and settings, Body Roll, alignment settings, etc. Several of these are the result of a number of components which if altered, will also alter how the car responds.

All of this assumes the car is driven in a steady state. Change the dynamic of the car, and the handling characteristics will also change.

Now, all this can be quite different when viewed subjectively by a particular driver using their own driving style, but there is still a static tendency which has been built into the car, whether the driver perceives it or not.

The Boxster is setup by the Factory for the Street. As such, it has a slight Understeer dialed into it because this provides safer, more predictable handling (especially at high speed), it is generally more forgiving, especially to a novice or inexperienced driver. But, Porsche also provides optional equipment such as stiffer shocks and springs, anti-roll bars, front transverse control arms with adjustable Caster settings, for those who wish to adjust the car for Track use...

Happy Motoring!... Jim'99

.....just to jump in

After a long time on stock S roll bars am contemplating a change. I feel that the car does not turn in sharply enough and lacks front end feel in turns. There is very little oversteer unless it is wet or I have cold tires.

I am on: 18s along with Michelin PSS (for the street); PSS9s; all three strut braces; adjustable rear toe bars. Tire pressure is 30 to 31 up front.

I was considering a change to: both M030 bars and urathane bushes; camber plates to get the top of the front struts solid.

Are there other specific bushings I can target to get some better driver feedback?

The hydraulic power steering only sends a limited amount of feedback through the steering so a Boxster will never feel like a go-kart or an air-cooled 911 in terms of steering feedback.

But reducing/tightening up any of the slop in the front suspension will certainly help. But I worry that it may not completely solve your issue.

A Boxster Spec car (with 255's in front and adj GT-3 sway front/adj sway rear) has huge front end bite into corners and provides ample mid-corner feedback so you might want to head in this direction by increasing front tire width, stiffen the front sway bar, and soften rear sway bar.

Find someone who will let you drive their Spec Boxster to get an idea of what it feels like. And yes, I'll offer a drive in my car if you want to come to Cali.

[sigh]

MNBoxster... the poster who at one point probably had more threads locked down on 986forum than anyone else.

Smart idea to have popcorn handy when Jim posted - LOL.

Good times :cheers:

Thanks, Tom I will definitely take you up on that! I may be out there looking for work soon!

Would just the GT3 bar upfront while leave the stock S in the rear provide a reasonable balance and starting point? I know many do it and it is all a matter of personal taste but I don't want to get into too much under steer......perhaps it wont be an issue as I am not on the limit at the track. I am just after some bite..

I am on 225s up front (265s rear) and it may be a while before I am able to source the right sport classic II wheel to handle the 255 tire. I think this may be 911 size somewhere in 993 996 18" offerings.