High speed oversteer and understeer

[MM2200]

In the coming months I'm going to spend a couple of days tracking my car for the first time.

I'm the sort who likes to explore the limits of what is possible, however considering the high speeds involved it seems worthwhile to have some idea of how things will be different from what I know now.

I am comfortable both inducing and controlling understeer and oversteer (mine is a FWD car) at low speeds (~45mph) via lift off/left foot braking/unbalancing the car and have a good idea of how the geography of a corner effects the car in these regards, but I want to know how things change at higher speeds.

Is it just a case of having to react/anticipate more quickly? Are there any 'quirks' in the handling of a car that typically show up at higher speeds?

What other things should I be considering at this stage?

Any help would be appreciated.

[Get Karter]

The car will travel further in the wrong direction at higher speeds.....so make sure there is enough space outside the track to allow you to perform these antics.

If there isn't enough space, then don't oversteer/understeer on the faster bends.

[GreenV8S]

At higher speeds the tyres will feel much less positive sideways and the car will be inclined to squirm around in ways that you wouldn't get at lower speeds. You are also likely to be closer to a steady state since you don't usually get hard cornering for long at low speeds, so you may find that the steady state handling characteristics are quite different to the ones you will get at low speeds. If the car does start to move around a lot you will find you can cover huge distances while you regain control. No problem if you've moving more or less where the road goes, rather more of a problem if you and the road are diverging. Before you explore the limits of the car at high speed think carefully about what would happen if the car understeers/oversteers, and limit your exploration to the places and modes that you think can be recovered safely. For example if you have a clear infield but no run-off on the outside you might decide that oversteer is safe but you can't afford to get into a tank slapper that might see you spearing off into the armco. You can plan your way around this, for example by planning to lock all four wheels if you feel the car may be turning in a direction you don't want it to go.

Edited by GreenV8S on Monday 15th September 16:42

[MM2200]

GreenV8S said:

At higher speeds the tyres will feel much less positive sideways and the car will be inclined to squirm around in ways that you wouldn't get at lower speeds. You are also likely to be closer to a steady state since you don't usually get hard cornering for long at low speeds, so you may find that the steady state handling characteristics are quite different to the ones you will get at low speeds. If the car does start to move around a lot you will find you can cover huge distances while you regain control. No problem if you've moving more or less where the road goes, rather more of a problem if you and the road are diverging. Before you explore the limits of the car at high speed think carefully about what would happen if the car understeers/oversteers, and limit your exploration to the places and modes that you think can be recovered safely. For example if you have a clear infield but no run-off on the outside you might decide that oversteer is safe but you can't afford to get into a tank slapper that might see you spearing off into the armco. You can plan your way around this, for example by planning to lock all four wheels if you feel the car may be turning in a direction you don't want it to go.

Edited by GreenV8S on Monday 15th September 16:42

This is just the kind of thing I was looking for, thanks.

I think I'll begin at the limit I'm currently familiar with and progressively push it up from there, with careful thought about what is likely to happen if it goes wrong and push the limits where it would be best for something to go wrong, if it must.

[bobt]

MM2200 said:

What other things should I be considering at this stage?

Some training with an expert. Most of us who think we are competent are woefully lacking in the high speed skills dept.

[Cathar]

Does your car have anti-lock brakes? I had to find out the hard way that with ABS your car _will_ travel where the wheels are pointing, no matter how hard you try to lock the wheels...

[DougBaker]

Cathar said:

Does your car have anti-lock brakes? I had to find out the hard way that with ABS your car _will_ travel where the wheels are pointing, no matter how hard you try to lock the wheels...

ABS will not get you round a corner which is too sharp for the speed you are currently traveling. If you reach the corner going too quickly ABS will just give you a little more control while you crash.

[mechsympathy]

DougBaker said:

Cathar said:

Does your car have anti-lock brakes? I had to find out the hard way that with ABS your car _will_ travel where the wheels are pointing, no matter how hard you try to lock the wheels...

ABS will not get you round a corner which is too sharp for the speed you are currently traveling. If you reach the corner going too quickly ABS will just give you a little more control while you crash.

In an out of control spin on track you want to get on the brakes hard and lock the wheels up to keep the spin predictable so you don't collect anyone else. With unlocked wheels or ABS operating you risk suddenly regaining grip and the car changing direction unpredictably.

[anonymous-user]

One thing to think about if you really do go high speed cornering oversteer (>80mph)is that some cars aerodynamic lift "gain" can be a very steep function with yaw (or more accurately body slip angle). This can manifest itself as large reduction in lat accel, which in conjunction with the reduction in Tyre Mu as tread slip increases can lead to some very long long slides at high speed! (anyone with a scooby or Evo particularly will know that if you really manage to get it sideways at high speed then it can keep going sideways for a long time/distance) It depends on the shape of your car, and how much negative lift (i don't use the word "downforce" with road cars as just about all still generate lift overall) the body shape / aero pack creates when at zero bodyslip angle.

And finally, remember with oversteer at high speed that too little applied torque is as bad as too much, get it sideways with power, then lift off the throttle totally, will see you round just as quickly as keeping it nailed! have fun!

[MM2200]

No abs. In spite of the lessened braking ability, I prefer this in that it allows me to directly grasp the relation between the output of car control from input of braking, without interfering electronics muddying the waters and giving me unjust confidence in what I'm doing.

Max, thats a very interesting point, one I have very little knowledge about. I've discovered the car moves about quite a bit more just going straight at higher speed than lower speed (and god forbid that there should be any crosswinds) and was wondering what effect it might have. If its a progressive effect then I'm not overly concerned, but the potential for some sudden propensity to change direction due to aerodynamic effect (or lack of it), I wonder about.