What happens? When I was in school a fellow pupil found out the hard way. He crashed.
On the vast majority of cars, the parking brake, also called the emergency brake (E-brake) or handbrake, only applies brakes on the rear wheels. Pull it delicately and the car will slow down. But apply enough force (assuming the brake is in good working order) and the rear wheels will lock. They stop turning and start skidding. Instead of faithfully following the front wheels, now they can also go sideways! That can be entertaining at low speeds in wet or snowy car parks and grassy fields. At high speed when you want directional control, it’s not good at all. A car going sideways puts it at risk of rolling, especially if it’s heavily loaded and/or strikes some obstacle like a curb.
So my fellow pupil was bounding along the road, 4 or 5 up in a small hatchback, at a good 60 to 70 mph. The front passenger, apparently knowing absolutely zero about cars, thought it would be a lark to pull the handbrake. He gave it a firm yank, the ratchet locked the brake on, and before the driver figured out what was going on the world was spinning! The car rolled over the pavement/sidewalk, grassy verge, across a ditch, somehow vaulted a 4 foot stone wall without touching it (Bonus! Less damages to the landowner.) and came to rest in a field. The car was totalled. Happily, everyone was wearing a seatbelt and survived, bar some bruising from flailing limbs.
So yeah, unless you’re a rally driver and really know what you’re doing, don’t touch the parking brake at high speed. It’s not funny.
Nick Leroy – likes cars but not a fanatic.
Source : Quora