Tread Depth versus Braking Distance
Your ability to stop will be governed to an extent by your car’s braking system and the adhesion of your tyres. Surprisingly, your car’s weight has little to do with stopping in a straight line, but heavier cars will encounter greater trouble stopping in a corner. Weight is generally a bad thing.
Assuming that your car doesn’t fall to pieces, your main allies for stopping are your tyres. Their ability to grip is loosely defined by the variable conditions of the road surface, over which you have no control, and by the quality of your tyres, depending on their make, tread and inflation, all of which you do control. Admittedly not at the precise moment when you panic-brake and the adrenaline is fizzing in your fingertips.
However, if you inspect your car’s rubber once a month and don’t buy cheap, then your odds of stopping short will improve dramatically when some wildebeest pulls out in front of you. Boring but important: under-inflation can extend your braking distance by 10 per cent, more if the car is loaded up with passengers. It can also reduce cornering power by a third.
In the wet your braking distance is about 40 per cent longer when the tyres’ tread depth reaches the legal limit of 1.6mm, and beyond that you’ll need a parachute. It’s best to change tyres when at 3mm on summer tyres and 4mm on snow.