OK, class, listen up: Figure A is what happens when your front tires lose grip. It's called understeer or push. Figure B is what happens when your rear tires lose grip. It's called oversteer or fishtailing.
By Jack Lanier
Understanding Understeering: You Are Not Alone If You Don't
01-04-2005
I once heard an engineering professor spend 10 minutes attempting to answer a question about how antiroll bars work. The professor was no doubt a very bright guy, thoroughly trained in the theory of suspension design, but he was speaking without using a single word legal in Scrabble.
His audience was mainly engineering school graduates, some were currently working in the automotive industry. All very smart folks, but few had much practical, hands-on knowledge. I'm certain some of the younger ones had never seen an antiroll bar. By the time the teacher had finished, everyone was thoroughly confused. That included me and, probably, the prof.
I was likely the dumbest and certainly the least educated guy in the room, but I have spent many hours fiddling with antiroll bars (which some call "sway" bars) and other suspension components on both race- and street cars and I have pretty much every book and video on racecar suspension. So I asked the person who'd posed the original question: "Did you mean to ask, 'Explain what happens when you fit a stronger-rate bar?'" He said, "Yes," and I responded: "A stronger bar reduces grip on that end of the car. Tightening the front increases push; tightening the rear bar makes it looser."
It was exactly what he wanted to know. I could see lightbulbs going on all across the room, but that may have just been people waking up because the professor had stopped speaking. If you need to know more on antiroll bars, start reading books on racecar suspension adjustment and design. Racers don't care a bit about theory; they just want to go fast, right now.
My points: Whether the group is engineering school grads, those who work in the automotive industry, racers or car writers, the knowledge base is often a lot lower than many think. And, a simple answer may be all that's needed. It may be all that the audience can understand.
A couple of paragraphs ago, I threw around a couple of terms "push" and "loose" that far from every reader fully understood. These are terms oval-track drivers use to describe what happens when the car reaches the limit of tire grip. When you're driving as fast as possible (or hit an icy patch on a freeway ramp), one end of the car inevitably loses grip before the other. If that's the front tires, the car is pushing (or "tight"). If it's the rear tires, it's loose. Think of it this way: With push, you hit the wall with the front bumper; with loose, you hit the wall with the rear bumper. Stock car drivers use another term: "free." This means the fronts and rears are sliding at about the same rateit's really fast, but the driver will have a hard time racing it that way.
Rather than push, loose and free, engineers and road racers use "understeer," "oversteer" and "neutral" to describe the same things. On a recent TV broadcast Darrell Waltrip I hope in jest got the terms reversed. A friend who worked on Can-Am teams in the '70s told me a champion road racer said "push" when he meant "loose." Know this: understeer = push = crunched front bumper; oversteer = loose = crunched rear bumper; free = neutral = faaaast.
Right now, many of you are like another engineer I met recently. He fully understood the meaning of understeer and oversteer: In fact, part of his job was producing three-dimensional graphs showing what all four tires on a racecar were doing at any one momentbut he didn't know what it felt like to have a car push or go loose. He was like a blind person who could describe the Mona Lisa.
Push/understeer feels like the steering column has suddenly transformed into rubber: You've got the wheel cranked left but the car isn't turning nearly as much as you'd like. In severe cases, it feels as if the steering wheel has snapped off: No matter how much you turn the wheel the car goes straight.
Loose/oversteer, to most highway drivers, feels much like hitting a tree or running into a ditch, because that's what their car does when it goes loose. A race driver battling a loose car feels what the outside rear tire is doing. Before the rear end steps out there's a lightness or, sometimes, shuddering in the outside rear tire: That's the tire saying, "Whoa, that's about all I can take!"
So don't feel inferior if you don't know all the terms bandied about by car writers, broadcasters and professors. They may not fully understand them either.
http://www.edmunds.com/insideline/do/Columns/articleId=104166#
<!-- end legacy --><!-- Footer content -->
