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Does braking using your left foot (like Formula 1 drivers would) make you a better/faster driver? And why?
Is it only better/faster if you don't have a clutch? So then it would not be impressive at all if you use your left foot to brake for mundane driving?
Left-Foot Braking can, in certain situations, result in better/faster racing times.
One common race situation that requires left-foot braking is when a racer is cornering under power. If the driver doesn't want to lift off the throttle, potentially causing trailing-throttle over-steer, left-foot braking can induce a mild over-steer situation, and help the car "tuck", or turn-in better. Mild left-foot braking can also help reduce under-steer.
In rallying left-foot braking is very beneficial, especially to front-wheel drive vehicles. It is closely related to the handbrake turn, but involves locking the rear wheels using the foot brake (retarding actually, to reduce traction, rarely fully locking - best considered a misapplication), which is set up to apply a significant pressure bias to the rear brakes. The vehicle is balanced using engine power by use of the accelerator pedal, operated by the right foot. The left foot is thus brought into play to operate the brake.
It is not as necessary to use this technique with Rear-wheel drive and All wheel drive rally vehicles because they can be easily turned rapidly by using excess power to the wheels and the use of opposite lock steering, however the technique is still beneficial when the driver needs to decelerate and slide at the same time. In rear wheel drive, left foot braking can be used when the car is at opposite lock and about to spin. Using throttle and brake will lock the front tires but not the rears, thus giving the rears more traction and bringing the front end around.
In restrictor plate NASCAR events, drivers were known to left-foot-brake at times, particularly in heavy traffic situations. Rather than lift off the throttle, which could lose considerable power and speed (due to the restrictor plates), a mild tap of the brakes while the right foot was still planted flat on the accelerator, could help avoid contact and bump drafting.
As far as normal road use goes, left-foot breaking can only realistically be recommended for cars equipped with automatic transmissions, which have far less control than manual transmissions.
The problem with automatic transmission is that, unless the driver drives 'two footed', he or she has far less control over the car than over a manual – which is why we read of many deaths and injuries caused by 'out of control' automatics. What usually happens is that during the engine's warm-up phase, or if the engine has been over-fuelling, the electronic control unit raises engine revs to above the point at which drive is taken up in the transmission, and the car starts to move. The driver may then panic, attempt to brake heavily, but hit the accelerator instead of the brake, and the car either crashes or runs someone over. (The phenomenon even has a name: 'Sudden Acceleration Syndrome'.) You cannot predict precisely when the car's ECU will increase revs independently, so my advice is to only buy an automatic if you can teach yourself to brake with your left foot at least while [sic] manoeuvring, which keeps the car fully under control.
First of all, efficient left-foot braking does typically require that you're not also on the clutch. In F1 cars, the clutch is controlled by either of two paddles under the "gear up" and "gear down" paddles, and so it's more natural to give the left foot responsibility for braking. As an aside, the average F1 steering wheel, with multiple electronic linkages to the transmission and powertrain, fuel injection system, brake balance system, front and rear wing adjustments, communications system, various LCD readouts including upshift and pit cues, and the fact that like everything in the cockpit it's custom-made for the driver out of the most lightweight materials, costs in the neighborhood of US$50k.
With a clutch pedal on the floor, you typically have to press both clutch and brake at the same time as you're both slowing and downshifting for a corner. The GT and rally drivers, who start with production vehicles and can't make extensive control setup mods like paddle shifters, do put in aftermarket clutches and make very precise adjustments to the pedal throws, giving the clutch, brakes and accelerator the same throw length (short). The pedals are also placed very closely together, allowing drivers to use an "overlap" position of their feet on the pedals; press the outside of the right foot for gas, press the outside of the left foot for clutch, press the inside of either for brake. This in turn more or less allows the driver to use whatever foot's handy to brake, left or right. If they're off the accelerator and downshifting for a hairpin, right foot. If they're slowing for a chicane or a drift turn but still under power, left foot.
In the average civilian vehicle, these adjustments aren't available; the pedals are spaced further apart (especially for large American clod-stompers), differently-shaped and differently-placed, and have different weights and throw lengths. Despite this, Rally Racing News recommends left-foot braking when driving a front-wheel drive car in a racing scenario. The basic idea in a FWD is that when both brake and accelerator are applied, the front wheels keep turning despite the braking, because they're under power, but the rear wheels slow, and so lose some of their traction, causing the rear end to kick out (oversteer; a hard thing to do in most American FWDs, which are strongly biased for understeer for safety reasons).
In a rear-wheel-drive car, this effect is even more pronounced but for the opposite reason; the car slows, transferring weight to the front wheels, and with the rear wheels still under power from the accelerator they will lose traction, kicking out the rear end. This in fact makes RWD cars really sensitive to applying brakes, accelerator and steering wheel at the same time; the general strategy in a RWD is to brake before beginning to turn, shifting weight to the turning wheels, then turn and accelerate through the corner as you straighten out. Braking while turning hard will cause the rear tires to lose too much traction, putting the car sideways in the corner, and when you add accelerator to try to power out of it, the car will swap ends.
