Stopping Distance
Every vehicle is equipped with a braking system to bring a moving vehicle to a complete stop. The most common braking systems are disc brakes, drum brakes, and anti-lock brakes. The automobile industry has seen huge advancements in reducing the braking distance of a vehicle but the overall efficiency of the braking mechanism is incomplete without taking into account the tires, road condition, and the driver itself. Let's talk about vehicle stopping distance and some of the important factors it depends on.
Reaction Distance
Reaction distance (thinking distance) is the distance traveled by the vehicle from the moment the driver realizes there is a need to stop to the moment the driver actually applies the brakes. The average reaction time of the drivers falls between 0.5 to 2 seconds, but this time can change based on various factors like:
- The speed of the vehicle
- Exhaustion and fatigue
- Influence of medicine and alcohol in the system
- Drivers' prediction for the need to stop
Braking Distance
Braking distance is the distance traveled by the vehicle from the time when the driver actually applies the brakes to the time the vehicle comes to a complete stop. Braking distance depends on various factors listed below.
- Tire tread depth
- Gradient of the road and road condition
- Load on the vehicle
- Speed of the vehicle
- Type of braking technology
Stopping Distance
Stopping distance is the combination of ‘Reaction distance’ and ‘Braking distance’ of the vehicle. Although this distance depends on various factors discussed earlier, a typical stopping distance for a passenger car at various speeds is displayed below.
How does tire tread depth impact stopping distance?
We are pretty familiar with the fact that the tires are the only physical means by which the vehicle makes contact with the road. The contact patch of the tire is responsible to provide the traction to convert the braking force into stopping force. Without proper tread depth, the tires lose their capability to traverse through various road conditions involving water, mud, sand, and debris. Lower tread depth creates a shallow passage through the grooves and mud, sand and water could not find a way to escape. This creates the condition where the tire loses the rubber contact with the road and the traction force is drastically reduced. In such a scenario when the brakes are applied with the intention to come to a complete stop, the vehicle experiences slipping and takes a comparatively longer time and distance to come to a stop.
Most passenger car tires come in 9 or 10/32nds of usable tread depth; winter, snow, and light truck tires may have more tread depth. A recommended safe tread depth limit is defined at 4/32”. Tires with a tread depth lower than this would not be ideal for daily driving conditions. Tires with a tread depth of 2/32” are considered legally worn-out in the United States. Although people measure the reliability of their tire with tread depth, the rubber compound in the tires deteriorates with time. It is recommended to change the tires every six years regardless of the tread depth remaining. Cerebrum Sensor’s intelligent tread depth calculator keeps track of the tread depth health and provides notifications for any services needed for your tire.
How do wet roads affect the stopping distance of a vehicle?
Things become pretty risky during wet and snow seasons with low tread depth tires. Such a combination is a cocktail for fatal accidents. Low tread depth tires running on wet roads result in hydroplaning. In this condition, there is a thin layer of water trapped between the tire contact patch and the road. This happens because shallow tread does not allow water or snow to easily escape outwards through the grooves. Trying to stop a vehicle in such a condition could result in losing total control of the vehicle. The vehicle would continue slipping and the driver would be unable to handle the vehicle unless the tires regain contact with the road.
A study by AAA concludes that a vehicle with a low tread depth of 4/32nd driving on a wet road increases the stopping distance by 80 feet. This means it will take much longer to come to a full stop. It is advised to keep bigger gaps between your vehicle and the vehicle in front to give enough distance for the vehicle to come to a complete stop.
How to calculate stopping distance for your vehicle?
There is a way to calculate the estimated stopping distance for your vehicle based on the current speed. This approach does not take into consideration the road condition, tread depth or other factors discussed earlier. It gives only an approximation considering the tread is healthy and the road condition is normal. Use the formula explained below.
- Check the vehicle speed, use the first digit of the speed, and square it. Now add zero to the end and divide it by 2.
- Double the vehicle speed, add the number to the result from step 1. The final number is the stopping distance in feet.
As an example, let’s say the vehicle speed is 70 mph. Taking the first number (7) and squaring it gives 49. Adding zero to the end gives 490. Divide this number by 2 results in 245. Now in the second step, doubling the vehicle speed (70) gives 140. Adding both these numbers results in 385 feet of stopping distance.
This resultant stopping distance can drastically increase with wet road conditions and high speed. That’s why it is advised to drive slowly on wet roads to avoid longer stopping distances which could result in severe accidents. Always remember, precaution is better than the cure. Drive safe!