If you have a car that was built in the last 10-15 years or so, there's a halfway decent chance that, somewhere within an easy reach of the driver's seat, there's a button, knob or switch labeled Sport. If you've never used it, you might wonder: what is Sport mode? Is it bad for my car? If you have dared to push it, you might have found that it made your car seem quicker as you bop around town, almost as though your ride found a few extra ponies in the paddock.
Well, that Sport button doesn't squeeze more horsepower out of your engine — but it might make you think it has.
A history of the gas pedal
See, once upon a time, a car's accelerator pedal was connected to the throttle directly through mechanical means, usually via a cable. That meant there was a fixed relationship between the travel of the gas pedal and the opening of the throttle that lets fuel flow into the engine by opening up. At its simplest, it was pretty much a direct correlation: push the gas pedal down 20 percent of the way, and the throttle opens up 20 percent as far as it can, etc.
By manipulating the linkages and cams, however, engineers could change this so that the car pushed proportionately more gas into the engine at the beginning of the pedal's travel — i.e. pushing the pedal down 10 percent opened the throttle 20 percent of the way, pushing it down 50 percent opened the throttle 90 percent. (This relationship between the pedal and throttle position is known as the throttle map.)
This, effectively, made the car feel peppier than a linear throttle map, as it took less force on the gas pedal to get the engine up to (or at least closer to) maximum power. Most internal combustion engines make maximum horsepower at high rpm; by tweaking the gas pedal so its travel was effectively front-loaded, it meant the car would accelerate more quickly at anything less than half-throttle or so — the zone of pedal travel where real-world drivers spend most of their time.
(The flipside, of course, is that pushing the pedal deeper into its travel produces proportionately less effect than it would otherwise — but for many people, the only time they push past half-throttle is to floor the gas, and that still produces the same result.)
Still, the relationship between gas pedal travel and throttle openings was always fixed: a certain amount of pressure from your right foot would always result in the same. Starting in the 1980s, though, carmakers began to move over to electronic throttle control, sometimes known as drive by wire in reference to fly-by-wire systems used in airplanes. In a car using ETC, there's no mechanical link between gas pedal and engine; instead, computers detect how far down the accelerator has been pressed, and use an electric motor to open the throttle and let fuel into the combustion chambers.
Well, it wasn't too long before some clever engineers realized that this computerized relationship meant that you could play with the accelerator/throttle relationship in ways you couldn't before. Specifically, since it was all just computer programming, you could offer more than one program. And that's exactly what Sport mode is on many cars: a second, more aggressive throttle map.
Here's what Sport Mode does:
Pressing that Sport button simply tells the computer controlling the engine to dump more gas into the engine earlier on in the gas pedal's travel. Under normal operating conditions, for example, your car's throttle map might tell it that pushing the gas pedal 20 percent of the way down means the throttle should open to 30 percent; in Sport, however, the throttle map might change to one where pushing the gas pedal down 20 percent means the throttle opens to 50 percent. Same push of the gas, but it squeezes more power out of the engine.
In some cars with automatic transmissions, activating Sport mode can also change the transmission's shift logic, activating a second program that tells the car to downshift more readily and hold gears for longer. Normally, automatics are programmed to shift up as quickly as possible for better fuel economy — but good gas mileage almost always comes at the expense of power, so most cars are relatively listless at the low rpm engine speeds that slushboxes try to seek out. Sport mode programming tells the gearbox to favor higher rpm, in order to keep the engine closer to the power band — the rev ranges where it makes the most horsepower and torque.
Of course, some cars — especially performance-oriented models — have Sport buttons that do more than that. Cars with active suspensions that can change the stiffness of their dampers will often firm them up when Sport mode is engaged, causing the body to roll and bounce less. Some vehicles will change the amount of assistance from the power steering system in Sport, making the steering wheel feel heavier and the car more substantive — or even change the steering ratio, so every degree of turn has a greater effect. And a few cars with brake-by-wire systems like the BMW M8 can even change the mapping for the brake pedal, so that the brakes bite harder earlier in the pedal's travel.
Still, for most of us, a change in the way the gas pedal works is all that little Sport button does. It doesn't squeeze extra power from the engine; it doesn't hurt it in any way. It just makes the car feel a little more zippy in everyday driving.