Concrete weights can be hung from the front or back of the tractor. Frames are built from angle iron or plywood. The frame is then filled with quick set concrete and allowed to dry. The amount of concrete used determines the final size of the weight, but 45 lb. to 50 lb. weights are ideal.
Cut a number of circles the same diameter as your lawn mower's tires from sheet metal using a cutting torch or grinder. Cut holes in the metal discs that align with the bolt holes for the wheel. Then, remove the tire and slide the weights onto the bolts and up against the hub before tightening the wheel back into position. Depending on the number of weights added, you may have to buy longer wheel bolts to do this.
Add calcium chloride inside your tire, either between the rubber tire and the tube or just inside the rubber tire if it is tubeless. This is a dense liquid that adds weight and stability to your tires.