Contour Enthusiasts Group Archives Forums General Autocross and Open Track Under vs. Oversteer

Please explain. . . Especially pertaining to Front wheel drive

Understeer is where you hit the wall with your front end. Oversteer is where you hit with your back end.

Understeer is generally more preferable from a loss of control standpoint, because you see where you're going and are in an easier position to regain/maintain control. I think it also scrubs off more speed. The wide majority of street cars are designed with balance toward understeering. Oversteer in a front-driver is generally an out-of-control condition, since we can't use the throttle to control the amount of oversteer angle, at least not as readily as a rear-driver can. A really good driver in a FWD car can toss intentional oversteer and use it to his advantage, but in most cases, bad idea.

Actually oversteer in a front wheel drive vehicle is every bit as easily (if not more easily) fixed with the throttle than it is in the RWD car.

The reason is becuase if a car is oversteering in the first place it's because the front tires are generating more traction in a lateral direction than the rears are. You can fix that two ways, either reduce the steering angle, reducing the turning force, or you can take traction off the front and add it to the rear. The way to do that is either get off the brakes if you were on them OR give it a little gas and whaddya know, it's not oversteering anymore.

But on a RWD car the oversteer is usually caused by too much throttle in the first place and you need to ease off the gas to regain rear traction, but if you jump off it too fast you do what you don't want, which is unload the rear tires, and around you go. If you got into the oversteer while on the brakes or otherwise off the throttle, the fix is the same as in a FWD car because physics is physics...you need to ease into the gas to get some weight to the back of the car. But in a RWD car it's easy to overdo it and make the situation worse.

Now to the general driver with no training, whose first instinct in ANY situation is to slam on the brakes, yes, a FWD oversteer condition is ugly but that's not to say it can't be fixed with the throttle, in fact that's the best fix.

I want to add to Jeb Hoge's post, and try to be a little more basic.

Understeer: The car turns less than you are trying to turn it, i.e. the front tire would rather go straight than the direction you are turning them. What causes this? Too much speed while turning, not enough grip/weight on the front tires while turning. Resolution for understeer, decrease speed until sufficient traction returns to front tires.

Oversteer: The car turns more than you are trying to turn it, i.e. the back swings out on you. There are different reasons for why this occurs. The biggest reason is loss of traction with the rear tires due to wheel spin (RWD) or lack of weight on the rear tires. The general response for oversteer is to counter-steer the wheel until the car stops rotating. Alternative responses will depend on the conditions which caused the oversteer.

Hopefully I kept it brief enough.

I guess I should have backed up and provided a more rudimentary explanation of what understeer and oversteer are. The explanation above is true but it's a summary.

First of all, FWD, RWD, makes no difference, the conditions called understeer and oversteer are the same in both cars.

Understeer is when the steering angle of the tires is more than the turning angle of the car, in other words it's "pushing" or "plowing", you're turning the wheel but the car isn't responding. As stated above, most cars are set up to do this naturally because it feels less scary to the uninitiated and also because it makes you more likely to hit anything head on where the restraint systems of the car can do their best work.

Oversteer is when the car's turning angle is greater than that of the wheels, in other words it's sliding tail-out, or "loose", or fishtailing or what have you.

The scary thing about oversteer for most people is it's more likely to happen suddenly whereas understeer is something most people sort of progress into in the course of a turn. For me, personally, understeer is more aggravating to deal with because your options are more limited. The reason is if the car is understeering you've overcome the combined abililty of the front tires to turn the car and to do whatever else you're asking them to do which is usually braking. You can't really add more brakes because that's part of what's exceeding the tires traction capabilities. You can't really add more gas because that'll further reduce their traction capabilities and make it worse. So what you have to do IF you're on the brakes already is ease off just a bit and fight all your natural instincts and actually decrease the amount of angle in the steering wheel. This will ask less of the tires so they have more traction and whaddya know, now it's turning like it's supposed to. But it takes a TON of mental power or built-up muscle memory to overcome your brain's "oh no!" instinct to both turn more and brake harder.

Now a FWD car will tend to have a lot more of its weight over the front wheels. And in any given situation the mass of the car wants to go straight, and since most of the mass of a FWD car is way in the front, the front wants to go straight in a turn. That's understeer. So you have to use some driving techniques to minimize the problem, principally "trail braking" which is when you stay on the brakes as you start the turn, loading the front tires and unloading the back tires, so the car will begin to rotate as you're easing off the brakes. This is THE way to get a FWD car to oversteer. Actually some of them will do it at speed simply by lifting the throttle and turning but most FWD cars want to push push push. And if you trail-brake you'll get it to turn and you may get it to oversteer and the beaty of oversteer at that moment is you can simply let off the brakes or if it's really bad give it a bit of gas and the situation is fixed like THAT.

And of course I started that long response before Andrew posted his...

That's all right, I started my response before reading your first post. We can just keep on overlapping .

Darrell Waltrip explained it best:

"Understeer is when you see the crash coming. Oversteer is when the crash sneaks up behind you."

Thanks for your responses!
Very helpful

Steve

In a nut shell:
Understeer = Car not turning enough
Oversteer = Car turning too much

Oversteer is sometimes a good thing, such as sliding around a corner (i.e. WRC racing on SpeedVision). This is when you want the arse end to come around quickly on a tight turn. I personally cannot think of a situation that understeer is welcome. Usually I curse my worn and all too narrow front tires. Does anyone know when understeer is a good thing???