Perhaps you’ve noticed: cars are very like canister vacuum cleaners the way they take turns. Say you are leading your vacuum cleaner into the next room and you turn too sharply; the trailing canister gets hung up on the doorjamb now doesn’t it?
And what happens to your car if you make a turn too tight in it? Your rear wheels strike the curb. The dreaded ‘Vacuum Cleaner Effect.’
That’s because only the front wheels are steerable - the rest just tag along behind. How closely the tag-along rear wheels follow the tracks of the front wheels depends mostly on the length of the vehicle’s wheelbase. Long trucks really have a problem with the vacuum-cleaner effect. That’s why truck drivers need to make these wide-swinging “buttonhook” turns. As a car driver you’re wise to look out for them lest you find yourself on the wrong side of a turning truck.
Honda offered four-wheel steering a few decades ago on its already agile Prelude. The expensive option appeared to be the answer to a question no one had asked and wasn’t met with great glee, or acceptance. But four-wheel steering on a bigger machine? Ah, that makes sense. And General Motors later offered 4WS on its Sierra Denali pickup and Suburban, though they marketed wrong and lost a good chance to lead with a truly desirable adjunct.
Four-wheel steering tightened the pick-up’s turning circle to that of a Saturn coupe, rendered it actually maneuverable in a parking lot and made towing appreciably easier and much safer. If you were one of those who saw the virtues of 4WS despite GM’s insistence in at first offering it only on its already expensive premium vehicles and actually own one — lucky you.
What four-wheel steering does is reposition the rear wheels to the most advantageous place for a given maneuver. Therefore at slow speeds the rear wheels turn in the opposite direction to the front wheels; at high speeds they turn in the same direction. Think about it: at slow speeds you want the rear wheels to accentuate the turning input of the front wheels; at high speeds you want them to understate the direction change (for instance, to ease a quick lane change while towing without risk of fishtailing.)
If I were spending dollars for options on a pick-up I’d most certainly put four-wheel steering ahead of leather seating, a sunroof or a killer sound system. GM should have done what Audi learned it had to do with Quattro, its four-wheel drive system. That is instead of offering it as an option for the top of the line only make it available at every trim level. If GM had done that from the beginning 4WS might still be available.
But how about your own little car with no 4WS and none really needed except maybe when you’re parking in one of those tight head-in spots. Here’s how to simulate four-wheel steering for a neater job of parking.
Ideally, there’s room to line up your entry to the slot with a wide turn. Failing that, once you’ve turned into the parking space unwind the steering and aim for the front door of the vehicle parked to the outside of your turn. Get as close as you can to it then again tighten your steering and pull fully into the slot.
What you do with this two-stage steering is advance your rear wheels farther into your parking slot thus assuring that your car will be more centrally sited in that slot, neatly spaced well within the lines. Just like with 4WS. Or like a cleverly maneuvered vacuum cleaner moving from the upstairs hall to the guest bedroom.
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