How Stuff Works

Auto Tech: Progressive throttles

June 24, 2009

This type of throttle movement, with a small movement of the pedal creating a larger opening of the engine throttle plates, is often a tuning “trick” used by auto manufacturers. Given two vehicles of the same size, weight and power, the one that opens the throttle plates faster will feel sportier and more powerful. However, it is also accompanied by using more fuel, so there is a penalty for that feel.

My son likes the throttle on my antique Thunderbird the best. The car starts to move as soon as you press the gas pedal and the power and acceleration are progressively related to the amount of pedal pressure you apply. Although the power is easy to apply, the belted tires on this antique make it twitchy to steer on anything but smooth pavement. Still, driving the T-Bird smoothly was the easiest, and with the top down, shoulder checking is the best of the bunch.

Electronics have changed how throttle control works. With drive-by-wire systems commonplace, the gas pedal is only connected to the computer. The computer controls the throttle plates based on all inputs, including traction control, engine temperature, gear selection and on some, vehicle driving style. It is now possible to have the throttle very responsive at low speeds if you select a lower gear and less responsive if you are in Drive range. If the tires start to spin, the traction control can tell the computer to reduce throttle, even though your foot position hasn’t changed on the gas pedal. All it takes is putting the right program in the computer.

On many 4×4 vehicles, selecting low range in the transfer case will modify the throttle rate as well. Driving smoothly over rough off-road terrain is difficult if the throttle is too responsive, so the manufacturers program it so a large movement of the gas pedal only causes a small opening of the throttle. Put it to the floor and you still have full throttle, but now the vehicle is easier to drive.

Drive-by-wire systems programming is continually getting better, making vehicles easier to drive. Even the most powerful sports cars can be idled around town without wheelspin, and small economy cars can have a sporty feel to the throttle too. The next time you drive your vehicle, think about how the vehicle responds to your throttle inputs.

Now all I need is an adaptive system that limits throttle response when it senses a teenager driving inappropriately. That would be the ultimate adaptive throttle control.

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