Breaking with Turning Wheels: The Science Behind Its Effectiveness

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In summary, breaking with the wheels turning is more effective than when the wheel locks up because static friction is always greater than dynamic friction between the tire and the road. This allows for better steering control and only slightly reduces braking power when using anti-lock brakes. Wide tires provide more grip because they have a lower risk of sticking or deforming, making them ideal for cars.
  • #1
madmike159
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Why is breaking with the wheels turning more effective than when the wheel locks up?
Is it because there is more friction between the breaks and the disks (or drums) than there is between the road and tyre, or am I missing something.
 
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  • #2
No, the key is always the friction between the tire and the road: static friction is always greater than dynamic (sliding) friction.
 
  • #3
The brakes on a car are usually stronger than the tire road friction as it is quite easy to lock the wheels in motion.

Anti-locking does not reduce the stopping power to any significant amount, but while the wheels are turning you can still steer the car instead of heading straight towards the object that made you brake in the first place. Usually locked wheels cannot steer even if you turn the steering wheel.

ABS will reduce braking power but in the range of instead of a 30m full stop, it might be 30.5 m. The added distance is small so the ability to steer comes first
 
  • #4
russ_watters said:
No, the key is always the friction between the tire and the road: static friction is always greater than dynamic (sliding) friction.

I'll read the pf page on friction.

*Edit*
I read it but don't get why static friction > dynamic friction.
 
  • #5
Friction is the normal force times the coefficient of friction.

The coefficient of static friction is always higher than the coefficient of kinetic friction (moving).

You can witness this by pushing a large block. It takes more force to get it moving than to keep it moving once it's going.
 
  • #6
madmike159 said:
I read it but don't get why static friction > dynamic friction.
Essentially, when something is stationary, the rough surfaces settle against each other, but when the surfaces are moving with respect to each other, they don't. They'll skip from one bump to the next.
 
  • #7
Abninfamy said:
Friction is the normal force times the coefficient of friction.

Yup, people are often suprised that it's independent of a surface area term.

So. Why do wider tyres give more grip than narrow tyres?
 
  • #8
Why do wider tyres give more grip than narrow tyres?

Yeah that question was bugging me for quite a while.

In bikes it is worth it to have greater stability during turns...but for cars....don't know.
 
  • #9
Friction is not independent on area, in practice. Small surface area will deform some materials, while to big and it might stick. The formula for friction is a bit more complicated than F=ymg. It depends on surface area (but it's mainly a small dependence if the surfaces are not at least on the order of 20x different) and speed of the two surfaces, this might explain why car tires should be wider, while on a bicycle nobody cares.
 
  • #10
The friction equation doesn't include surface area because it is a already part of the coefficient of friction. So that doesn't imply that friction is independent of surface area.
 

FAQ: Breaking with Turning Wheels: The Science Behind Its Effectiveness

1. What causes a vehicle's wheels to lock up while braking?

Locking wheels while braking is usually caused by the driver applying too much pressure on the brake pedal, causing the wheels to stop rotating and lose traction with the road surface. This can also occur if the brake pads are worn out or if the brake fluid is low.

2. How does locking wheels affect a vehicle's stopping distance?

Locking wheels can significantly increase a vehicle's stopping distance. When the wheels lock up, the vehicle loses its ability to steer and may continue to travel in the same direction, making it difficult to stop quickly. This can also cause the vehicle to skid, which increases the stopping distance even further.

3. Can anti-lock braking systems prevent wheels from locking up?

Yes, anti-lock braking systems (ABS) are designed to prevent wheels from locking up while braking. ABS uses sensors to detect when a wheel is about to lock up and then releases and reapplies the brakes rapidly to prevent the wheels from fully locking up. This allows the driver to maintain control of the vehicle while braking.

4. How can locking wheels affect a vehicle's handling?

Locking wheels can significantly affect a vehicle's handling. When the wheels lock up, the vehicle loses its ability to steer and may continue to travel in the same direction, making it difficult to maneuver or avoid obstacles. This can also cause the vehicle to skid, making it harder to control and increasing the risk of an accident.

5. What are some tips for preventing wheels from locking up while braking?

To prevent wheels from locking up while braking, it is important to maintain a safe following distance from the vehicle ahead and to avoid sudden and excessive pressure on the brake pedal. It is also important to keep the vehicle's brakes well-maintained, including regularly replacing brake pads and checking the brake fluid level. In addition, it is recommended to keep both hands on the steering wheel and to steer in the direction of the skid if the wheels do lock up.

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