Dear Car Talk: OK, so my cruise control is set, the car is moving at its set speed, and I apply the brake. The cruise control disengages and the car slows down. Scenario 1: I apply gentle pressure on the accelerator to slowly return to my desired speed (as if there were an egg between my foot and the pedal) before turning the cruise control back on. Scenario 2: I click the cruise control’s “resume” button to return to the desired speed. The car accelerates much, much faster than it does when I accelerate it manually. Which way is more economical – the cruise control’s way, or my way?
Your way. The “resume” feature of cruise control used to be a whole lot worse, actually.
In the old days, you’d hit “resume,” the transmission would downshift a gear or two, snap your head back, dump your hot coffee in your lap and make you hold on for dear life.
Back then, there was a vacuum-operated device that – when you hit “resume” – would yank on the bell crank of the throttle, opening it instantly to the position where it should be for your desired speed – say, 65 mph. And if you were going 40 at that moment, and suddenly the throttle were open to where it needs to be for 65, the acceleration would be pretty intense.
These days, cruise controls are smarter and smoother, because throttles are all computer-controlled. So “resuming” isn’t as likely to result in an emergency visit to the chiropractor.
Most people don’t even realize that there is no longer any physical or mechanical connection between the gas pedal and the throttle. Instead, the computer measures the position of your gas pedal, sends a signal to a small motor inside the throttle, and that motor moves the throttle plate. And the computer-controlled motor can move the throttle far more smoothly and gradually than the old vacuum-operated yanker.
But, no matter what technology you’re using, accelerating gently always is better for the car. So if your foot can accelerate the car more gently than your cruise-control system can, and you’re not ticking off your spouse or an angry, sleep-deprived truck driver behind you, gentle foot pressure is the way to go, Richard.
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