Try focusing on one of these wheels in the illusion. It will not move. Now move your eyes around the other wheels and you will see them all rotating. By focusing again on any wheel individually, it will stop turning, but the wheels around it will.
The illusion also works if you look away from the image, but keep it in a corner of your sight.
When we focus on one wheel, our brain tells us that it is stationary and we understand its pattern. However, when we move our eyes, the patterns of all the wheels confuse our senses.
Focus on one wheel, and you see it's not moving. But move your eyes around from one wheel to the next, and all of them appear to be spinning.