Q: My son tells me that our car has too much understeer. Is that bad?
A: Like many automotive words, the terms understeer and its opposite, oversteer, are often misunderstood and misused. To be able to drop these terms properly into conversation, start here.
Understeer is nothing more than a vehicle’s natural tendency to continue going straight ahead -- rear wheels following front wheels -- in resistance to a change in steering direction. It’s called “plowing or pushing” and occurs when the slip angle of the front tires is greater than the slip angle of the rear tires. All front-heavy, big-engined vehicles -- which cover the great majority of domestic vehicles -- understeer. The major drawbacks can be excessive tire sidewall and wheel alignment wear as the vehicle leans, fighting against the turn. Safety experts point out that understeer gives the driver the greatest chance for control and recovery in case of misjudgment on turning angles.
At the opposite pole (“of inertia” a bad pun for my engineer friends) is oversteer; a handling condition in which the slip angles of the rear tires are greater than the slip angles of the front tires, compelling the vehicle’s tail to swing wide and occasionally to "swap ends," as the rear of the car rotates toward the front. An oversteering car is referred to as "loose." Classic examples of oversteering cars are the early Porsches -- primarily because of their engine location in the rear. An oversteering car is inherently more dangerous because of its "breakaway unpredictability" -- that is, the unfixed speed or position at which the rear of the vehicle breaks traction and spins toward the front. Obviously, early Porsches were considered extremely dangerous -- especially in sports car racing -- because of this tendency to, as the drivers said, "bite them in the rear without warning."
Can understeer and oversteer be eliminated? Probably not in conventional vehicles. However, a mid-engined car has most of its mass within its wheelbase, giving it neutral steer.
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