use lead, it isn't magnetic. what does allow the cars to move to magnets are the cars that come with metal axles and wheels. these are magnetic and a bit of a design flaw. BUT they will also sell you very small coil springs that you put one of on one axle over the pin point bearing end and it acts like 'just on' handbrake that adds little resistance to the car, but enough to stop it getting sucked to uncoupling magnets.