I am from India and I have a one month old commuter bicycle. I have once tried adjusting front wheel using the quick release, but I haven't removed the tire. How do I know if the wheel is correctly centered?
There are several meanings to "centered" and it's unclear which you mean:
Hub centered laterally between the forks: The quick releases and/or axle nuts do this automatically for you when you scrinch down on them. See: What do the conical springs in quick releases actually do?
Hub centered in the drop-outs: this is the most important. You want to make sure that the axle/quick-release fits as far into the drop-outs that it can go. Cinch up the axle nuts or quick-releases part of the way, then grip the brake levers (or have a friend grip them) as you fully tighten the nuts/quick release. That'll help ensure that the wheel is centered.
The above requires that your brakes are rim-brakes and are relatively centered. If not, you can use the top of the fork or the chain stays as a way to visually ensure your wheel is centered.
That your wheel itself is in true (a perfect flat disc) and not wobbly. See @CarpeTony's answer for that.
If your brakes are rubbing, or the wheel is rubbing on the frame then you probably need to adjust the wheel or the brakes.
The quickest way to check is to use the brakes.
1) Pull the brake lever for the front wheel as far to the handlebar as it will go. It should be at least a finger width from the bar at full compression.
2) While watching the brake pads, the part of the brake touching the wheel, let up slowly on the lever until the pads are almost touching the wheel but not quite.
3) The pads should both be clear of the wheel. If one come clear first then either the brake needs adjusted or the wheel is not centered in the frame.
4) If both brakes clear the wheel at the same time then start turning the wheel slowly while continuing to hold the brake just clear of the wheel. If there's a problem with the wheel one side or the other will hit a brake pad.
You can take it to a shop if the wheel needs to be trued.
If it's a front wheel, and you don't have disk brakes, the first thing to try is this:
First, assure that the axle is all the way seated into the notches (dropouts) in the fork ends. There should be no space between the axle and the end of the notch.
Use a ruler to measure the distance between the rim and the fork tube. Do this on both sides and write it down. The two distances should be nearly identical, within 1/16" or 1mm.
Remove the wheel and insert it in the opposite direction (flipping left and right sides).
Measure the distances again. Compare the first and second sets of measurements. Note that you should compare the distance measured from the left fork tube in both cases and the distance measured from the right fork tube in both cases, vs comparing distance measured from the "same" side of the flipped wheel. Again, the distances should be nearly identical.
(I don't suggest measuring from the brake blocks to the rim because the brakes tend to wobble a bit when you remove/replace the wheel.)
If any of the above measurements are off by more than about 1/8" or 3mm then something is wrong. (Perfectionists will argue for smaller tolerances, but I'm being practical.) If the distances don't change when you flip the tire then the fork is probably bent. If the distances do change then the wheel is not properly centered, and it probably needs to be "trued".
However, do note that a possible reason for the off-center wheel is a wayward washer or nut on the axle. When you remove the quick-release "skewer" from the axle, the two ends should appear to be essentially identical. If there is a nut or washer one end that is not on the other end then that may be your problem.
Shop wise, you could use one of two tools.
- Trueing Stand
- Dish Tool
The former will make sure the wheel is straight, and show you how much runnout there is. It can also show you, if correctly aligned, if the rim is centered over the center of the hub--this of course is a little different for the rear wheel where the hub is not necesssarily centered because of the cassette/freewheel.
The dish tool will show you if the rim is centered in relation to the outer faces of the axle nuts. This is one of the surest way to know your wheel is centered.
If you do not have those tools, the brake pads can be used in a pinch to straighten a rim, and with at least the front wheel you can use your eye to see if they are centered in the fork.
Depending on the frame, you can do the same for the rear.
You'll find a lot of information there.