Internal magnetic resistance system for use with fitness device

An internal magnetic resistance system for use with a fitness device, comprising:

• an axle;
• an inertia wheel rotatably disposed at the axle and having a lateral surface, the lateral surface having a protruding ring portion;
• a transmission wheel rotatably disposed at the axle and connected to another lateral surface of the inertia wheel, the another lateral surface facing away from the protruding ring portion;
• a magnetic permeable ring having an outer circumferential surface fixedly disposed on an inner circumferential surface of a protruding ring portion of the inertia wheel;
• and
• an electromagnet disposed in the protruding ring portion of the inertia wheel and surrounded by the magnetic permeable ring, wherein the electromagnet has a support, iron cores and coils, the support being fixedly disposed at the axle, the iron cores being disposed at the support, spaced apart relative to the axle, and separated from an inner circumferential surface of the magnetic permeable ring by a gap, and the coils winding around the iron cores, respectively.