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Oversteer vs Understeer
Question:
With all the talking about FWD vs RWD here, I have a question. What exactly are RWD cars’ understeer and FWD cars’ oversteer? How would one feel it when driving? (I have driven lots of FWD cars and some RWD cars, but I guess I just never paid attention to the difference in steering).
RWD, rear wheel drive FWD, front wheel drive Understeer, a condition when the vehicle turns less than the input from the steering wheel. Oversteer, a condition when the vehicle turns more than the input from the steering wheel. Factors involved in causing under/oversteer, vehicle design,speed, body roll, tire flex, and the abillity of the tires to adhere to the road. — The more you learn, the better your luck.
Response:
Imagine a car circling a skid pad in an exact circle at a constant speed. If you lock the steering wheel to maintain the circle, then very gradually increase the speed, an oversteering car will start turning in a tighter circle; an understeering car will tend outward and increase the radius of turn. A car with neutral steer characteristics will stay on exactly the same path.
Hmmmm. A car with neutral steer will stay on exactly the same path? I thought any time the tires begin to lose their grip (whether it’s the front tires, the rear tires, or both), a car would tend towards a wider circle. With understeer, the car loses its ability to "turn in" because the front tires are skidding. With oversteer, the car actually turns sharper than it needs to, but the rear tires skid outside the desired path. And with neutral steer, the car turns in just the right amount, but the whole car skids somewhat towards a larger circle. -Dan
Response:
With all the talking about FWD vs RWD here, I have a question. What exactly are RWD cars’ understeer and FWD cars’ oversteer? How would one feel it when driving? (I have driven lots of FWD cars and some RWD cars, but I guess I just never paid attention to the difference in steering). Thanks. –Alex.
oversteer: a state in which the car tries to ditch itself on the inside of a corner understeer: a state in which the car tries to ditch itself on the outside of a corner You feel it when you’re taking an exciting corner and the car just doesn’t seem to want to go exactly where you want it to. Generally takes some rather spirited driving for the average driver to notice it. Certainly not something you’ll see coming back from the corner store with a quart of milk on the seat beside you. Bob Benson
Response:
With all the talking about FWD vs RWD here, I have a question. What exactly are RWD cars’ understeer and FWD cars’ oversteer? How would one feel it when driving? (I have driven lots of FWD cars and some RWD cars, but I guess I just never paid attention to the difference in steering). Thanks. –Alex.
Response:
Newsgroups: rec.autos.misc Organization: University of Pennsylvania Lines: 7 NNTP-Posting-Host: lonestar.resnet.upenn.edu With all the talking about FWD vs RWD here, I have a question. What exactly are RWD cars’ understeer and FWD cars’ oversteer? How would one feel it when driving? (I have driven lots of FWD cars and some RWD cars, but I guess I just never paid attention to the difference in steering).
Technically speaking, oversteer and understeer are two kinds of response to increasing lateral acceleration. Imagine a car circling a skid pad in an exact circle at a constant speed. If you lock the steering wheel to maintain the circle, then very gradually increase the speed, an oversteering car will start turning in a tighter circle; an understeering car will tend outward and increase the radius of turn. A car with neutral steer characteristics will stay on exactly the same path. Oversteer is fundamentally an unstable condition; the decrease of radius will increas the lateral acceleration, which decreases the radius still more, further increasing lateral acceleration until the limit of adhesion is reached and the car just slides and spins out. Understeer is basically more benign; the car will just stabilize at the larger turn radius. Neutral steer is practically impossible to obtain over the entire operating regime of a car (speed, load, turn radius, temperature, road roughness and camber, etc). Cars are generally set up to understeer, some much more than others. Some factors tending toward understeer: o Front-heavy weight bias o Higher rear tire pressures o Larger rear tires o Greater roll stiffness in front o Suspension geometry and compliance o Tractive force on front tires (acceleration or braking) o Dynamic weight transfer toward rear, as under acceleration (this is why I said "gradually increase the speed" above) Some factors tending toward oversteer: o Rear-heavy weight bias o Higher front tire pressures o Greater roll stiffness in rear (viz "Rear wheel lifts" thread) o Tractive force on rear tires o Dynamic weight transfer toward front, as under deceleration Often one or more of these factors is used to offset others, for example Porsche 911’s with fat rear tires and stiff front anti-roll bars to offset the oversteer effect of its rearward weight bias and rear drive. The VWs that lift a rear wheel in cornering are also showing this: the rear roll stiffness is high to counter the front weight bias, so the inside rear wheel, which started with a small static load, is unloaded completely under the right cornering conditions. — -Stephen H. Westin The information and opinions in this message are mine, not Ford’s.
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