Oversteer/Understeer

[Superman]

I've got a simple question. My SC understeers like CRAZY at autocross. The more I mash the throttle, the more it pushes. To rotate the car, I lift.

I have never done a 'Drivers Education Day.' At speed, do these cars still understeer? If so, do they rotate a little easier when you lift the throttle?

[kwah]

completely normal.

[Trackrash]

At very fast speeds there will be more of a tendency to oversteer, unless you have a rear wing.

If you are serious about autocrossing you need to go with bigger torsion bars and if you size them correctly you will have a balanced car.

911s, and any street car for that matter, is set up from the factory to understeer. Much safer if you realize the front is loosing grip before the rear does. The older 911s had a habit of suddenly oversteering if an unsuspecting inexperienced driver made a mistake.

When Porsche started putting larger tires on the rear this issue was largely resolved.

There are a number of factors that can affect the ballance of a 911. But the soft springing of the stock torsion bar 911 can lead to frustrating handling. The front end will lift under power exiting a tight turn leading to a pushing situation.

[Superman]

The car has 22/29 torsion bars and Carrera sways.

[Trackrash]

Originally Posted by Superman

The car has 22/29 torsion bars and Carrera sways.

Interesting. In my case I had 22/28 torsions and even though the car felt good, it would understeer coming out of thight turns.

I changed to 22/30 and no more understeer. At lest not that I could not control.

In your case you should consider stiffer shocks, or better yet, externally adjustable shocks. Also adjustable sway bars. And perhaps larger rear torsions, if the rear of your car is squatting during corner exits.

[Superman]

Thank you. The rear sway bar has some adjustability. That said, I am not sure whether to stiffen or loosen the rear sway in order to cure understeer. I know that stiffer rear torsion bars can control understeer.

[danco_]

Stiffen the rear swaybar to lessen understeer is how I always understood it.

[Trackrash]

^^^ True. A little goes a long way.

The first thing I would check is to see if the rear is squating during corner exit. I think that your torsions are close to what you want, however. But it's worth looking at.

There are a number of other things that can affect you car' s balance.

I have found that when I lowered my front end it reduced my corner exit push. Other things to consider are alignment and tire pressure. Do you use a pyrometer to check tire temps? Shoe polish can tell you a starting point for tire pressure as well.

What tires are you running? What sizes?

[Driven97]

Mashing the gas is going to equal understeer in an SC in most situations. The rear engine equals massive traction. Hitting the gas plants the rear, and removes weight from the fronts. That equals understeer.

AXing a 911 quickly requires getting the car rotated early. You can then use that trait to your advantage by getting to WOT early.

You can reduce your steady state (skidpad, constant velocity, light throttle) push with spring/alignment/swaybar/tire, but you're not going to have a drift machine at corner exit unless you double your horsepower, or alternately pitch the car in sideways at entry.

[IROC]

Originally Posted by Superman

The car has 22/29 torsion bars and Carrera sways.

Basically the same as my car with the same behavior. I've only done two autocrosses in my life, so I can't speak to that, but in my experience, 911s tend to understeer in slow corners and then transition to oversteer in faster turns. The objective in my case was to dial out as much understeer as I could while retaining "neutrality" in the high speed turns. I found that increasing front tire width was the key. I went from 185s, to 195s, to 225s and finally to 245s. 245s were the sweet spot.

[Bill Verburg]

Originally Posted by Superman

I've got a simple question. My SC understeers like CRAZY at autocross. The more I mash the throttle, the more it pushes. To rotate the car, I lift.

I have never done a 'Drivers Education Day.' At speed, do these cars still understeer? If so, do they rotate a little easier when you lift the throttle?

In a 911, gas is glue for the rear

In any extreme maneuver a car is mostly on 2 wheels
braking - 2 fronts
acceleration - 2 rears
lefty - 2 right sides
righty - 2 left sides

The other wheels have proportionally less influence on what happens

over/under depends on speed, stock they are very conservatively setup for massive understeer, that's the safe way to be

understeer increases is the same as saying oversteer decreases

No matter what the base setup is as speed increases so does oversteer(another way to look at it is understeer decreases), aero is useful to counter this but at most A/X speeds aero isn't a significant factor.

For track use cars are set up for low speed under which transitions to high speed neutral

A/X cars are set up for low speed neutral to over which transitions to over or massive over

A/X cars will want more grip in the front than a track or even street car

to get more front grip, ie more over/less under
wider front wheels and tires, narrower in back
lower profile front tires, taller in back
more t-bar and sway rate in back, less in front
more aero in front, less n back
more weight in back, less in front
softer front shock, stiffer rear
more neg camber in front, less in back
higher front tire pressure, less in back(to a point)
wider front track, narrower in back

all of the above need to be applied carefully for a dual use car. You really don't want it to go too far.

[Tom '74 911]

I would agree with most of what's been said. To compliment the hardware and setup changes mentioned already, I'd suggest that you need to adjust your driving technique. Autocross is the perfect place to experiment. Do some reading on the traction circle and trail braking etc... you need to learn to rotate the car in a different way. I always find it helpful to get a ride with someone who can show me how it's done - I'm always surprised at how far under the limit I am relative to really fast drivers...

[Bill Verburg]

Originally Posted by Tom '74 911

I would agree with most of what's been said. To compliment the hardware and setup changes mentioned already, I'd suggest that you need to adjust your driving technique. Autocross is the perfect place to experiment. Do some reading on the traction circle and trail braking etc... you need to learn to rotate the car in a different way. I always find it helpful to get a ride with someone who can show me how it's done - I'm always surprised at how far under the limit I am relative to really fast drivers...

Braking is a very useful tool for A/X to get the car rotated, some guys w/ 3.2 Carrera will pull the p/v, the additional rear brake helps rotate the car, but it also makes it more challenging in other braking situations

Skill and technique are hugely important

[ted]

Originally Posted by danco_

Stiffen the rear swaybar to lessen understeer is how I always understood it.

True statement, but I prefer to try and add grip.
So if he had an adjustable front sway bar I would soften the front adjustable sway bar first.

[darrin]

Superman -- take a driver's ed class, it'll open your eyes to a lot of stuff (weight transfer, braking hard to set up a car for a turn, etc.). I'd strongly suggest "becoming one" with your car BEFORE throwing money into it . ..

[IROC]

Originally Posted by Bill Verburg

Braking is a very useful tool for A/X to get the car rotated, some guys w/ 3.2 Carrera will pull the p/v, the additional rear brake helps rotate the car, but it also makes it more challenging in other braking situations

Yes, trail braking and then using the throttle to immediately catch and plant the rear end as one dances to the apex is one of the pleasures of driving a 911.

[gduke2010]

Originally Posted by Superman

The car has 22/29 torsion bars and Carrera sways.

Have you ever had it corner balanced and aligned? It made my car handle much better.It's a cab with stock tor. bars.

[Superman]

Yup, it's been corner balanced before. These cars are persnickety about that.

[SCOTITUDE]

just askin? no flaming
how does a guy with a basic noob 911 question have twenty thousand posts?
boxster forum transfer?

[Superman]

No problem. I thought I knew the answer when I asked. Been a 911 owner since early 2000. This is my third SC. I bought it maybe ten years ago for $8K. It was tired, but I had all the parts I needed from the one that got totaled. '83 engine, freshened, with cams and '78 fuel distributor. Wishing for Webers. bronze suspension bushings, torsion bars, blah blah. I was pretty active here for a time, then got distracted for several years, now I'm b a a a c k.

I've plenty o' seat time at AX but none at speed. I'll learn about handling at speed on public roads. This is why I ask. Perhaps I will visit a local track a time or two. I have some idea how to handle the car in AX. I want to know more about handling at speed.

Make sense?