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

[Peer]

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

[MNBoxster]

Originally Posted by Peer

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

[Sammy]

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.

[Peer]

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

[pecivil]

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.

[Perfectlap]

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.

[John V]

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.

[1JB]

Originally Posted by John V

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.

[Topless]

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.

[MNBoxster]

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

[John V]

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?

[Topless]

Originally Posted by bmussatti

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.

[MNBoxster]

Originally Posted by John V

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.

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

Originally Posted by Topless

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 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.

[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.

[Topless]

Originally Posted by bmussatti

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.

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.

[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.