13 replies to this topic

[Christiaan]

I have been playing several games with over and under steer options and it seems I cannot come to grips with a car unless it has knife edge precisely balanced steering. I could not understand why I canno predict the behaiviour of a car with either setups. This led me to believe that I must be wrong in my understanding of what over and understeer is.

So, can anybody give me a nice technical explanation

Thanx
Chris

[Ursus]

Basicly, as I understand it, oversteer is when the rear wheels reaches it traction limit before the fronts, and understeer is the opposite. Understeer makes the car feel as it doesn't want to turnas much as you turn the wheel. Oversteer makes the car feel as if it wants to turn more than you turn the wheel. You can setup a the car to over or understeer with neutral throttle. Over/Understeer can also be induced with the throttle(in a reasonable setup car). Releasing the throttle ia turn will shift the wheight forward causing oversteer. Applying throttle will cause understeer by shifting wheight rearwards.

I hope this helped some. I know this reasoning works in GPL . Ofcourse if you got some downforce that will also play a part.

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Ursus
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[This message has been edited by Ursus (edited 12-17-1999).]

[PDA]

ursus - nice explaination. However, in F1 cars, the C of G is so low (compared with a saloon car) that the weight transfer on braking or acceleration is very low, so the induced over/understeer due to this is minimized.

One or two addditional factors on simple set up: Increasing roll stiffness at, say, the front will increase weight transfer to the outside wheel, unloading the inside wheel, thereby reducing overall grip at that end of the car, and inducing udersteer. Do the same at the rear and oversteer will result. Roll stiffness can be increased by higher rate springs, or a thicker anti roll bar.

[Christiaan]

Thanx Ursus, only I still can't see how I can make his work for me. You see, it makes more sense for me to always lose traction from the rear rather than the front. This simply because you control the front wheels and so if you lose traction, you still have a degree of control over the car.

[Ursus]

Always losing traction in the rear first is not a very good idea as you have to make constant lightning qick corrections with th steering. Or go rear end first into the scenery. An understeering car is somewhat better as you are less likely to lose control (car will tend to go straight until grip is regained/car slow a bit)

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Ursus
Trust me, send money.

[Sean L]

In general a front wheel drive car will understeer as cornering limit is approached while a rear wheel drive will tend towards oversteering.

A car that understeers is fine for a roadcar (mainly FWD) because it is safe - lifting of the throttle will generally allow the front tyres to grip thus tightening the cornering line. Alternatively steering a little straighter (i.e. turning slightly away from the apex of a corner) very briefly will also allow the tyres to regain traction before turning in again. Either way a loss of speed helps a lot...

For racing (being mainly RWD), understeer is the least desired handling characteristic as you tend to lose cornering speed due to having to back off and because your line will drifting away from the apex. Marginal oversteer on the other hand can be controlled by expert drivers with steering corrections and throttle inputs so that speed through a corner can be maximised.

MS likes his car to have a neutral balance with a slight bias toward oversteer. With the limited grip from the hard compound grooved tyres he doesn't mind the back sliding around as long as he's got good turn in at the front. Well he's one of the few with the talent to control an F1 car with the backside all over the place.

Most F1 drivers try to get it as neutral as possible.

[Yelnats]

In setting up Sim racers and I have found that a tendency to quick spins can be reduced by softening the spring rates and raising the ride height.

This slows the reactions of the car to directional changes as the roll center is higher and a slight transition is achieved as the car rolls to it's cornering attitude. This transition allows the driver a bit more time to react to an incipient spin which take slightly longer to begin.

This won't make up for a poor setup with too much front or rear roll stiffness (Understeer or oversteer) but it allows us mere mortals to control a F1 car at speed. Gods like Schumacher or Senna run (or ran) very stiff setups which maximised the reaction of the car to steering inputs but are uncontrollable by most F1 drivers and sim racers.

It's best to set-up the car with slight understeer in high speed turns as an oversteer spin at high speed occurs too suddenly for anyone to control (except for maybe Montoya or Schumacher). This is accomplished by putting more rear wing on until the car plows slightly and scrubs off high speeds going into the corner without spinning and then powering away from the apex.

In slow speed corners on the corner entrances, understeer is the killer, so put as little roll resistance on the front as consistant with acceptable high speed handling and hopefully the nose will come around to the apex and the throttle can be gently used to accelerate out of the corner.

If a driver uses various steering aids (tracion control, anti spin and ideal line), all your efforts to eliminate understeer may be negated as the steering assistance does strange things like removing steering lock and backing off throttle to prevent spins. So if you are serious and drive with a wheel, turn the aids off so you can feel the effects of your setups without the masking effects of steering assistance.

[silver]

Yelnats mentoined that Schumi uses stiff setup.
Actually nowadays there are two drivers in F1 who tend to use a lot stiffer setup than others. They are MH and JV and Mika is the one who has the stiffest setup.

Thats why his car always seems like on the rails but when it breaks away you can clearly see that Mika has to apply really fast corrections with the steering wheel.
That is also the reason why Mika is not so strong when it starts to rain in the middle of the race and everyone is on dry setup like in Nurburgring. It is because his car is extremely unforgiving due to stiff anti-roll bars and suspensions settings.

Some experts are even wondering how Mika is able to drive such an unforgiving car. He has the fastest reflexes of them all (at least in 1995 he had them) which help him a lot.

[Marco94]

Funny thing is however, that all things being equal, the softest car is the quickest car.

The ultimate cornering potential of a soft car is bigger then of a stiff car. This distinction between "soft" and "stiff" applies to the roll behaviour of the car. When the car is soft, it's dynamic tyre loads are smaller then when the car is stiff. This produces the best cornering potential. However, the driver does not have a very good feeling of what the car is doing. That's why the cars are generally a little stiffer then engineers would want them to be.

[mtl'78]

A key setup for a controlled oversteer is brake bias. Set to rear 60%+. Underbraking for a corner, the rear wheels will lock first, allowing you to better correct your entry line. Oversteer is faster, because the answer to understeer is always : go slower, wheras oversteer, you can correct through steering or MORE throttle/speed.

[Ursus]

60%+ at the rear? Isn't that WAY to much? That would mean that your braking capability would be really reduced. Unless you have some really strange wheight distrubution.

But I agree on oversteering is faster, while understeering is "safer"

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Ursus
Trust me, send money.

[silver]

One really cannot say which is faster setup oversteer or understeer.
For example in F1 there have been champions who have preferred both understeering and oversteering cars.
It is really up to the drivers to set the car up to their likings and make most of them.

If understeering is slow how come then drivers like Prost and Senna were so fast?

In F1 if your rear wheels lock you will go off, that is for sure. Those cars are so unstable and speeds are so high that is is simply impossible to go into the corner while your rear wheels are locked.

The reason why some drivers have a lot of brake bias towards back is very simply. They are usually drivers who turn-in with the brakes on. A lot of brake towards back stables the rear end of the car while going into the corner.

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Only two things are infinite; universe and human stupidity; and I am not sure about the former
-Albert Einstein-

[Jonathan]

You all may not aggree with this but as a young man (maybe 20 years ago) I read that the typical Grand Prix Driver would add front roll stiffness, giving something of a basic mild understeering additute, and then deliberatly overcome this tendancy though use of throttle induced oversteer or atleast nutrality.

I.E. under steady state corning the car would understeer, and the driver would compansate for this via application of the right foot. I belive the term for this was known as "steering with your feet".

I dont know if this technique still applies in modern F1 racing, however.

[mtl'78]

Understeer never allows the driver to surpass the limits of adhesion. As soon as you go over the limit, the driver must get more weight at the front, so he brakes.

Oversteer however, crossing the limit of adhesion, allows the driver several options:

he can lift off, he can try and opp. lock, or he can use the brake.

60% rear brakes is what I use in my limited race experience, and in all of the more realistic simulators. However, I don't recomend using it in real life until you've practiced. I learned the technique from a friend of my grandfather's who raced F3 and F2 in the 50's and 60's.

It makes the car extreemly sensitive, it does reduce overall braking efficiency, and makes the car oversteer more than you could imagine.
But it IS faster. One thing it does, is to force the driver to "learn" his brakes very well. The loss in efficiency is useful for overtaking. It makes you much faster on the entry into corners, giving less stopping power and more control. the weight gets shifted to the front wheels, and you still have full steering control, as your fronts don't ever lock up.

The main penalty is handling. You have too much of it. It requires the driver to "know" his car, and this technique will only be successful if the drivr is able to "anticipate" the reactions of the car.

Whenever I've driven a new car, I set up the brakes 60% front, and gradually reversewd it, as I got used to the car.

This technique allows you to be more aggressive/forcefull in the carthen an understeer setup would be. Oversteer is for drivers who'se strengths are car control, and oversteer is for drivers with excellent timing.

Drivers like Prost Lauda, and Senna to a much lesser extent were "timing" drivers. They made very few mistakes in the car. telemetry often showed that Prost would take a corner at speed 4-5 times in qualifying, and the angle of his steering motion varied less than 2 degrees over all 4 laps. that's why they (Prost Lauda) were often called robot/computer drivers. They have the ability golfers have of being able to repeat exact movements over and over with little or no variation. except they did it at 300 kphs,

All things being equal, a good driver will be faster in an oversteer setup. AS Robert Duvall said it in that God-awful movie: "Loose is fast"