If you've just received your Gigabyke and the tires are flat, it is likely due to the tires being intentionally deflated for shipping purposes, and not a defect of the inner tube or tire. This can be fixed by inflating the inner tube. Locate the valve that protrudes out from the rim, and with a bike pump with a Schrader valve or an air compressor with a 1/4" ball foot air chuck, inflate the tire to its recommended PSI. Note that not all tires have the same recommended PSI.
If your tire is balding or cracked or is not holding air pressure, then let's carry on to fixing this problem. Depending on which wheel you'll need to fix will determine what tools you'll need to use. For the front wheel you'll need: Tire levers Tire pressure gauge 12mm socket and ratchet 14mm socket with a second ratchet, or 14mm wrench For the back wheel you'll need: Tire levers Tire pressure gauge 10mm deep socket, 10mm wrench 5mm allen wrench/hex key 21mm wrench or large adjustable wrench Cable ties Preferred cutting tool for cable ties I'd recommend having a container handy to collect loose screws and other small parts. And of course, you'll need your replacement tire or inner tube. If you decide to use a patch kit to repair the inner tube, be aware that this is usually a temporary solution. If metric tools are not available, the SAE Imperial equivalent can be used, if those are more readily available, but check for proper conversions. If you don't already have tire levers or replacement parts, they can be purchased from Bikeberry.com or check with your local bike retailer. Let's start by taking the weight off the wheel you'll be working on. Using a bike jack will provide the easiest and safest results to elevate the wheels off the ground. Alternatively, the rear wheel can be raised by using the built-in center stand, and shifting the weight over the back wheel will raise the front wheel. If using this method, be sure to have additional help to support the bike and hold it steady. Now that the wheel is elevated we can get to work. The front wheel can easily be taken off by using a 12mm socket and ratchet to undo the axle, and a 14mm socket with a second ratchet or a 14mm wrench to hold the nut as we undo the axle. We want a socket for the 12mm bolt because of the tight fit around the fork eyelet that would prevent most wrenches from turning. In addition to a socket, The 14mm nut can use a box or open-end wrench because there's just enough room to securely grab onto the nut, by aligning the wrench with the eyelet. Now that the axle and nut are undone, hold the wheel and carefully slide the axle out of the wheel hub, making sure to catch the spacers as they come loose. Once the axle is pulled all the way out, the front wheel should easily slide off the fork. Taking off the back wheel will take a few more steps than the front wheel. Start by undoing the rear fender and side panels. The fender is attached by (6) 5mm allen screws, also known as hex screws. The side panels are each attached by a single 10mm screw. Once these are off, we'll have access to the remaining screws. Undo the adjusting nut on the brake rod. This should be loose enough to unthread by hand, otherwise, use a 14mm deep socket or wrench. Pull out the brake rod, catching the spring and other accessories. Undo the 10mm screw which supports the brake drum. Now that the brake components are undone, use a 10mm wrench or deep socket to loose the chain tensions. Us a 21mm wrench or an adjustable wrench to loosen the lock nuts and axle nuts on the back wheel. If you're struggling to undo these nuts, use a soft mallet and tap on the wrench. Loosen the nuts as needed until you are able to slide the wheel along the horizontal dropouts. Leave the axle nuts on if possible, to prevent the attacked components on. Before attempting to remove the wheel from the horizontal dropouts, remove the chain from both the drive sprocket and rear sprocket, clearing it away from the dropouts. Check for slack on the electric wiring that connects to the rear wheel. If there is not enough slack to remove the wheel completely, follow the wires and cut the cable ties along the way until there is a sufficient amount of slack to remove the wheel. Now that your wheel is free we can start to remove the tire from the rim. Relieve any air pressure that may be in the inner tube, by depressing the plunger in the valve. A pressure gauge can be used if it has a deflator pin, if not, any tool small enough to fit inside the valve will work. Now that the tire is deflated, press both sides of the tire towards the center of the rim, separating the bead of the tire away from the rim's sidewall. Use a tire lever and slide the hooked end in-between the lip of the rim and the tire bead; avoid inserting it near the valve. Once you feel the tire lever hooked under the tire bead, push the tire lever towards the center of the rim, lifting the bead over the rim. If the tire is loose enough, slide the tire lever along the rim, lifting the rest of the tire over the rim. If it is still a tight fit, use a second lever; lifting another section of the tire. This should be, 5-6 inches away or about 15cms from the first lever. Continue until the tire lever easily slides around the rim, lifting the bead completely over the rim. If there's enough room, the tube can now be pulled out. If there isn't enough room, the tube should come out when removing the rest of the tire. Now you can completely remove the tire from the rim. The second bead should easily be pulled off without the need for levers.
Now that the tire and tube are completely removed we can inspect the tire, tube, and rim to find out if there are any problems we are not aware of and to remove any debris or sharp points that may cause future problems. Inspecting the rim can be done by looking closely all along the inside of the rim and carefully feeling for debris and anything that can damage the inner tube. The same process is applied to the inner wall of the tire. When inspecting the tube, over inflate it slightly to make any perforations more noticeable. Submerging the tube in a bucket of water can help find perforations. At this point, we can grab the new tire or tube, or begin to patch the existing tube.
Once we're ready to put the wheel back together, we can start by placing the tube inside the tire, and seated so it evenly fills the inside of the tire. Search the outside tire walls for any arrows or print specifying the direction of wheel rotation. Begin placing the tire and tube on the rim by aligning the valve with the valve hole, making sure it does not protrude out in an angle. Slip the bead of one side of the tire back onto the rim. This should be loose enough that no tools are needed. Now that half the tire is on, check to see that the tube is properly seated inside the tire and not protruding out of the tire body. Finishing off the rest of the tire, we'll start by the valve and push the bead inside of the rim. Move out from both sides, pushing the tire back into the rim until the bead on the opposite of the valve is the only part not inside the rim. Massage the tire back and forth periodically to make sure the tube is not pinched between the tire and rim. At this point, the tire will start to feel tight around the rim. Finish that last part by sliding a tire lever in-between the tire and rim and lifting it outwards to force the remaining tire into the rim. If it is too tight for one tire lever, try a second one for more leverage. Now that the tire is completely on, massage the tire one more time to ensure everything is seated properly. Inflate the tire partway and check that the tire does not have sections that sit high or low. If it is not even, deflate and massage the tire and tube into place. Inflate the tire to manufactures specified PSI and begin the wheel installation. Start by sliding the wheel into the dropouts. If the front wheel is being reinstalled, align the wheel hub with the eyelet and slide the axle rod part way. Add the spacers and washer along the way as you insert the axle rod to the wheel's hub and through to the other eyelet. Us the 12mm socket and 14mm socket or wrench to tighten the nut and axle rod to the fork. If the back wheel is being installed, slide the axle rod, into the dropout and hand tighten the axle nuts. Be sure that the brake drum and components are in their proper orientation. Place the chain onto the rear sprocket and align the chain with the drive sprocket, using the pedals to pull the chain full on. Tighten the chain tensioners just enough to take out some of the slack in the chain. Fully tighten the axle nuts and locknuts. Screw the brake drum back to its bracket and reconnect the brake rod. Inserting the rod along with its guides, placing the components back along the way. Tighten the adjusting nut, periodically squeezing the brake lever to feel the tension. Reinstall the fender and side panels to complete the bike.
Congratulations! You're all set for more adventures on your Gigabyke.