The width of the tire for a mountain bike depends on the type of riding you plan to do. For cross country riding, a narrower tire with a width of 1.9-2.25 inches would be suitable as it provides less resistance on smooth surfaces and is lightweight. For trail riding, a wider tire with a width of 2.25-2.5 inches is preferable as it provides better stability and grip on technical terrain. And for downhill riding, a wider tire with a width of 2.4-2.8 inches is recommended for better traction and shock-absorption.

Tailwhip on a mountain bike involves rotating the back wheel of the bike while in the air behind the rider. To do this trick, you need to first gain enough speed and jump off a ramp. Then, you need to flick the back wheel in one direction using your feet while rotating your body in the opposite direction. As the wheel rotates, you need to jump and bring your legs back on the pedals to catch the bike and land smoothly. Practice and perseverance are key to mastering this trick.

To take off the rear tire of a mountain bike, first, shift the chain to the smallest rear sprocket. Loosen the quick-release or axle nuts on both sides of the wheel. Lift the bike off the ground and pull the rear wheel out of the dropouts. Finally, remove the tire by depressing the valve stem to release air pressure and use tire levers to take the tire off the rim.

To change a mountain bike chain, first, remove the old chain using a chain tool. Then, measure the new chain to the appropriate length by laying it over the old chain and lining up the pins. Use the chain tool to break the new chain to the appropriate length and attach it to the bike by using a chain link. Finally, adjust the derailleur to ensure smooth shifting with the new chain.