RAC Cars News


How Quickly Can You Stop Your Car?

By raccars Published

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Do you remember learning stopping distances for your driving test? No, most people don't, and yet all cars take a certain distance between pressing the brake and arriving at a stop. This is called the stopping distance and varies, depending upon how fast you are travelling, while other variables include the road conditions and driver reactions. Understanding stopping distances helps you to judge what sort of gap you need to leave between your car and the one in front of you, and the faster you are travelling, the greater that distance needs to be.

Learner drivers work on a table that adds a 'thinking' time to the amount of distance a car requires to stop once the brakes are pressed. The distances are expressed in metres and car lengths to help visualisation. For example, an emergency stop at 40mph requires 12 metres of thinking plus 24 metres of braking, for a total stopping distance of 36 metres or nine car lengths. At 70mph, you need 96 metres of stopping distance, which is 24 car lengths.

It has been proven that reaction or thinking times increase significantly with tiredness and drugs or alcohol consumption. Distractions, such as conversations with passengers or using a mobile phone, can increase reaction times even more. A zero tolerance approach is recommended in these cases - don't drink or take drugs when driving and do not use a mobile phone or indulge in emotional conversations when you should be focusing on the road.

Braking distances can also be affected by weather conditions. Rain, snow and ice will all make it difficult to brake from speed, while remaining in control of the vehicle. You have to work on the assumption that wet roads will double your stopping distance, so in the rain at 40mph, you will need more than 70 metres of stopping distance, and at 70mph your stopping distance goes up to almost 200 metres. If there is ice on the road you need to double that figure again - so 144 metres from 40mph and nearly 400 metres from 70mph, although you probably shouldn't be travelling at that speed anyway if there's ice on the road.

However, one factor which is often ignored is the condition of the car. To achieve standard stopping distances, you need well maintained brakes and sufficient tyre tread - a legal minimum of 1.6mm. Tyre pressure can also affect stopping distances - don't under or over inflate your tyres. The correct pressure can usually be found in the owner's manual and sometimes in a sticker inside the driver's door.

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