26x1.95" rear bicycle wheel

Sounds like a bent rim or it's out od square in the frame.
To check the "Out of Square" measure the distance from the rear axle to a point on the frame on each side of the bike. To check the rim for trueness; take the wheel off the bike mount it on a holder (or just hold it out at arms length with both hands and have someone spin the wheel; if it spins straight, the problem is being out of square on the bike, if it wobbles it's a bent rim.

Ask a local Bike Shop. Derailleurs for that bike are cheap. Evaluating the bike for a bent derailleur hanger and fixing it is a job for the pros. Word to the wise. Never pedal backward or roll the bicycle backward if it is the rear derailleur is not precisely aligned with a gear. It WILL rip bend or the derailleur right off.

http://www.parktool.com/blog/repair-help/hub-overhaul-and-adjustment

Slightly bent is unacceptable.

Google this "fix bent bicycle rim" for many answers and videos.

The actual 'fix' will depend a lot on how it got bent. Many bicycle shops can lace a new rim onto your existing hub and spokes but you may find it cheaper to buy a new wheel.

Unfortunately there is no way to narrow the rear spacing on that particular bicycle. 145mm was the intended spacing to use a beefier wheel. If you try to bend the rear triangle yourself you risk several problems:

• not bending either side the same amount leading to a wheel that is not straight inline with the rest of the bicycle
• binding the suspension pivots
• introducing fractures in the rear triangle welds (aluminum is not meant to be bent too much)
• breaking the rear triangle

Your best bet is to find a wheel that fits. Many tandems use 145mm spacing for the rear wheel, or you could find downhill-specific wheels and/or hubs to build up or use.

The set screws in the center of the axle are there to keep the axle centered in the frame. Only the right wheel is powered which also means only the right wheel brakes when operating the rear brake. This is because the rear wheels must be able to spin independently when turning because the outside wheel will move faster. Unfortunately no one builds differentials at this price.

If you have wheel wobble you need to determine if the axle is bent or the wheel is not true. Prop up the rear of the bike on a stand and remove the problematic wheel. Manually pedal the bike and check the axle as it spins. If the axle is wobbling then it is bent and will need to be replaced. If it spins true then the wheel is the culprit.

The axle is relatively inexpensive and can be ordered through a Schwinn dealer. Any bike shop should be able to true a wheel for around $15-$20.

I can tell you by my own experience that the click at every rotation is because the bearings on the BB, I had the same in my bicycle and after install a new crankset and BB it went away. I installed a Shimano Deore Hollowtech II and it works nicely and no noise.

Make sure the wheel is secured straight with the frame. Or look at the chainring and make sure it isn't bent.

Just take it to your local bike shop. They should be able to fix it. The wheels/tires are basically small bicycle wheels/tires.