What is the difference between magnet ring and metal ring?

In a car's ABS system, the magnetic ring and the ordinary metal toothed ring (usually called a Metal Ring or toothed sensor ring) perform similar functions, but their characteristics and working principles are quite different.

We can compare them in the following aspects:

□ Appearance and Structure

Metal Ring: This ring is easily recognizable; it looks like a small gear, with metal teeth neatly arranged around the ring. It's made of solid steel and feels rough to the touch.
Magnetic Ring: Its surface is usually flat and smooth, looking like a black rubber or plastic ring. But its secret lies within – beneath that smooth surface are many tiny magnetic poles.

□ How the Signal is Generated

Metal Ring: The sensor faces these metal teeth, and each time a tooth rotates past, the magnetic field is disturbed, generating a signal. This is like putting your hand in front of a rotating fan to block the airflow.
Magnetic Ring: It actively emits a magnetic field. As it rotates, the internal positive and negative poles alternately pass by the sensor, and the sensor directly detects the fluctuations in magnetic force. This method is much more sensitive than the metal toothed ring.

□ Advantages and Disadvantages Comparison

Resistance to Dirt:
Metal Ring: Dirt or grease can easily get stuck in the gaps. If the gaps are completely blocked, the signal will be affected.
Magnetic Ring: The surface is flat and less prone to accumulating dirt, but it is particularly susceptible to iron filings. Because it is magnetic, it will attract small iron particles like a magnet, which can interfere with its function.
Size:
Metal Ring: Usually larger and takes up more space.
Magnetic Ring: Can be made very thin and small, even integrated directly into the bearing's sealing cover, saving space. This is why more and more cars are using it.

□ Symptoms of Failure

Metal Ring: Mainly susceptible to rust or broken teeth. If the rust is severe, the signal will be intermittent.
Magnetic Ring: More susceptible to high temperatures and strong impacts, as these can cause demagnetization (loss of magnetism). Furthermore, if it's installed incorrectly, it will completely lose signal, whereas metal rings typically don't have a specific orientation.