3d print the mold and cast the tires in a more suitable material, you can use a large syringe and inject the rubber on the 4 mm hole untill it comes out of the vents, use m4 screws and nuts to put the mold together around the rim, be careful that the extra holes align so you have a continuous thread pattern, make sure to take the air out by vibrating it and then injecting a little more to fill it