The last thing you want to deal with while cutting the grass is a flat tire on your riding lawnmower. Although you can plug the tire temporarily, the best way to fix it is to replace the tire. Replacement tires for your riding lawn mower are available at hardware stores and lawn tractor dealers. Changing a flat tire on the mower is very similar to changing the tire on your car. The biggest difference is that riding mower tires do not use lug nuts. Once you have the wheel off the mower, take the flat tire off the rim and install a new tire.
Park the riding mower on level ground and place the mower in gear. Shut the mower off and apply the brakes.
Place a hydraulic bottle jack or floor jack under the mower and raise the mower up until the flat tire is off the ground. Position the jack near the flat tire under a frame piece of the mower.
Remove the center cap from the wheel hub with pliers. Removing the cap reveals the C-clip and washers that secure the wheel to the spindle. Pull the C-clip off the spindle by grabbing the closed side of the C-clip with a pair of needle-nose pliers. Slide the two washers off of the spindle as well.
Bleed out all of the air remaining in the tire by pressing the inside of the valve with a flat-head screwdriver. The portion of the tire that fits inside the rim on both sides is known as the tire bead. Lay the tire flat on the ground with the outside of the rim facing up. Insert a tire tool or flathead screwdriver between the lip of the rim and the tire bead. Lift the tire bead over the rim by pushing down on the tire tool handle or screwdriver handle. Insert another tire tool 6 inches away from the first and pry the tire bead out of the rim.
Slide the second tire tool around the perimeter of the tire bead and rim while the tire tool is still between the rim and tire. Continue all the way around until the outside tire bead is off of the rim. Pull on the inside tire bead off of the rim with your hands. If necessary, use the tire tools to aid in starting the inside bead off of the rim and then pulling the tire completely off of the rim.
Place the new tire over the rim at a 45-degree angle and push as much of back side of the tire over the facing rim lip. Use the two tire tools to pry the rest of the back side of the tire over the rim. Press in on the front side of the tire to start placing the front side inside the rim. Use the tire tools to aid in installing the final few inches over the rim. Care should be taken when using the tire tools to pry the tire on the rim so that you do not damage the bead.
Apply tire bead seal with a paintbush around the beads on both sides of the new tire. Place the wheel back over the axle spindle on the riding lawn mower. Install the two washers over the spindle and install the C-clip over the spindle. To install the C-clip, set the open end on the side of the spindle. Open up a pair of pliers and place one jaw on the outside of the C-clip and the other jaw over the opposite side of the spindle above the C-clip's path. Squeeze the pliers together to literally pull the C-clip over the spindle. Rap the spindle cap back on the spindle with a rubber mallet.
Place a ratchet strap around the perimeter of the new tire and tighten the strap down until the tire beads rest on the inside rim lip. Lower the mower with the jack until the tire slightly touches the ground. Use an air compressor to fill the tire with air. You may have to "pop" the beads tight by tapping the tire with the rubber mallet while filling the tire with air. Remove the ratchet after the tire beads have sealed to the rim. Finish inflating the tire to the recommended PSI on the sidewall. Lower the mower and remove the jack.