Car skidding on road

Factors that affect your stopping distance

What is stopping distance?

Many drivers don’t realise that stopping distance isn’t the distance it takes for your car to stop when you press the brake pedal.  Your stopping distance is the distance travelled from when you realise you need to stop. It combines your thinking distance and your braking distance.

Your vehicle’s stopping distance will be affected by many factors. Road conditions, tyre tread depth and how alert you are as a driver will all have an impact on how quickly you’ll be able to stop. 

To help keep you safe on the road in all weather conditions, we’ve created this guide to look at which factors will affect how quickly your vehicle can stop, particularly in an emergency.

How thinking distance effects stopping distance

Stopping distance = Thinking distance + Braking distance

It takes time for a driver to react to a situation and start to apply the brakes. The car carries on moving during this reaction time & the thinking distance is the distance travelled in this time.

The thinking distance increases if the reaction time increases. This can happen if the driver is:

  • On drugs or medication
  • Is tired or stressed
  • Is distracted
  • Is under the influence of alcohol

Reaction time and thinking time will greatly affect how quickly your vehicle can stop in an emergency. Be aware that when driving there are many factors that can cause reaction time to be increased, for example if you are on any kind of medication or have been drinking, your reaction time will be significantly slower, thus decreasing your stopping distance.

Stopping distances may also be affected if you are tired, so try not to drive for long distances when you haven’t had a good rest. It’s important to be aware that people around you, phones or other objects can also be major distractions, and therefore this can delay your reaction to something that would require you to brake suddenly.

 
Man on mobile phone driving car
car in rain

Road conditions

How road conditions impact stopping distance

Many people fail to realise just how much road conditions can affect the stopping distance of a vehicle. When road conditions are wet, icy or covered in snow/sleet, they are naturally slippery and can have a great impact on your stopping distance. 

In the rain and wet weather, your cars’ stopping distance will be TWICE as much as that in dry weather. It is essential therefore to make sure that you maintain a greater distance between you and the vehicle in front. This is to make sure that you have enough time to brake and come to a complete stop safely when necessary. 

Snow and ice can also have huge impacts on your stopping distance. Standard summer tyres harden in colder temperatures and so don’t grip effectively on icy or snow covered roads. This is why many drivers choose to opt for all weather tyres or specialist winter tyres which are designed to cope with freezing conditions.

Tyre wear affects stopping distance

The effect of tread depth on your stopping distance

The condition of your tyres has a huge impact on your stopping distance and can mean the difference between you being safe on the roads and being in danger. 

The tread of your tyres is designed to channel away and disperse surface water on the road. If your tyres haven’t got adequate tread depth then water cannot be dispersed quickly enough and you’re at risk or skidding or even aquaplaning.   The more worn your tyres are, the longer it will take you to stop.

Tests have revealed that a tyre with the minimum tread depth of 1.6mm travels 7.8 metres further than a tyre with 3mm of tread. This is why we always recommend changing your tyres when they reach 3mm, rather than 1.6mm.
tyre on wet road
tyre pressure

Tyre pressure

How does tyre pressure effect your stopping distance?

Tyres need to maximise their contact with the road in order to provide the best possible stopping distance. It is imperative that your tyres are neither over nor underinflated.
 
Underinflated tyres will make more contact with the road on the outer edges of the tyre whereas overinflated tyres will make more contact in the centre. 
 
As a result of this, your tyres will wear irregularly as well as reducing the traction. This means that your tyres will be less effective at gripping onto the road surface and bringing the car to a stop, therefore increasing your stopping distance. This is why it is so important to make sure that you check your tyre pressures regularly (around once a month) to ensure that your tyres are wearing evenly and maximising safety and grip on the road to reduce your stopping distance.

Speed

The effect speed has on your stopping distance:

The speed you are travelling at greatly affects your stopping distance. Stopping distance is braking distance + thinking distance, so the faster you are travelling, the more your thinking and breaking distance will increase. This means that your stopping distance is, in turn, going to increase too.

When travelling on faster roads, like the motorway, ensure you leave as much distance between you and other vehicles as possible as your speed is likely to be much faster than that on a quiet residential road. At the very least, follow the 2 second rule for safety. 

The 2 second rule means keeping a minimum of a two second time gap in front of your vehicle (double in poor weather such as rain and even more in snow and ice). This means you will create sufficient space in which to react to any emergency that happens ahead of you.

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