The steering system is the collection of components that allows you to control the direction of your cycle. It consists simply of your handlebars and stem.
Handlebars can be straight, or curved metal bars onto which the grips and brake levers are fitted. The stem is the metal "shaft" that connects the handlebars to the fork.
What you should check for?
Your handlebars should be checked for damage or cracks and to make sure they are securely anchored. The stem should also be checked for damage, make sure it's lined up properly, is securely anchored and that the extension "limit" (the furthest point that the stem should be extended out of the head tube) hasn't been exceeded.
Steering Problems and Solutions
If you notice handlebar movement, check that the clamp bolt(s) is securely tightened. If there is still movement after tightening this bolt, consult an experienced mechanic.
If you notice stem movement or if you just need to adjust your stem, you can make changes by loosening the stem expander bolt. This bolt is located inside your stem. The tools needed for this adjustment will depend upon the type of expander bolt you have. The bolt head itself should be located at the top of the vertical section of your stem, where the stem bends to meet the handlebars. To adjust, loosen this bolt until the stem rotates freely. Be careful not to loosen too much or the expander nut may drop into your fork tube.
If the stem is still difficult to move even after the stem expander bolt has been loosened, tap the bolt head firmly with a padded hammer. This will jar the expander nut inside the steering column free.
Once you've adjusted your stem and have it in the right position, simply re-tighten your expander bolt so that it holds the stem firmly in place. If you have an A-head stem replacement of bars, adjustment etc. is much easier.
Road bike handlebars
Stand facing the front of your bike and straddle your front wheel. Place your hands on the brake hoods, then gradually put your weight on them. The brake hoods and bars should be able to support your weight without rotating downwards.
Mountain bike handlebars
Follow the same procedure as above, but place your weight on your bar end extensions. If you don't have bar ends, try rotating your handlebars by pushing up and down on your brake levers. If you notice movement, check closely to see if your bars are rotating in your stem or your bar ends or brake levers are loose.
Straddle your bike facing forward and hold the bike frame steady with your legs. Turn your handlebars so that they are perpendicular to the frame. Check to see that your stem lines up parallel to both the top tube of the frame and front wheel. Then make sure that your stem is held firmly in place and that the minimum insertion line is not visible on the stem.
Special notes on stems and brakes
Before performing any adjustment, check to make sure that your brake cables are not attached directly to your stem. If they are, any significant stem movement may affect your brakes.
Stems, like seat posts have limits to how far they can safely be extended out of your frame. If your stem limit line is visible, don't ride your bike until you've adjusted this. If you can't ride your bike comfortably without the stem extended beyond its limit line, stem extenders are available or alternatively purchase a different stem.