New bicycles come with stems (the component that holds the handlebars) that are sized according to how big the frame is. As bicycles get larger, stems get longer and vice versa. Consequently, there's an excellent chance that if your bike fits, your stem is the right length and you don't need to worry about it.
The exception is if you're experiencing problems such as neck, back, hand and shoulder soreness during or after rides. And/or if you find that you have difficulty maintaining bent elbows while riding or feel the need to move forward or backward on the seat all the time. These are signs that the reach might be wrong and that swapping stems could be a good move.
Like other bike-sizing issues, it's difficult to judge stem length without help because you can't look at yourself in action. Also, you may not know enough to recognize signs that indicate change is needed. If you decide that's the case, come in to see us and we'll take a look and make recommendations.
If you'd like to check the fit on your own, one in-the-ballpark test is to hit the road or trail, warm up until you're comfortable and then look down (when it's safe) at your front hub (the center of the wheel). If you can't see the hub because the handlebars are blocking your view, it's an indication that the stem is probably the right size. If you see the hub and it's out in front of the bars, it's a sign that a longer stem may be needed. And, if it's behind the bars, a shorter stem should solve things.
A more accurate way to gauge stem length is to video yourself riding on a trainer (shot from the side), or get someone to watch. You can then look at the video (or ask your helper questions) to find out how your position looks. Ideally, your back will be flat (no hump), your head and neck will rest at a comfortable angle, your shoulders will be dropped (not hunched), your arms will be slightly bent, and an imaginary plumb line dropped from the tip of your nose would fall about an inch behind the handlebars. Keep in mind that this is a description of how you should be able to ride no matter what type of bike you use or how much you exercise. If you can't, chances are the stem is the wrong size and will cause you problems on longer rides.
If you're not sure what to look for, you might check sideview photos of professional riders in books and magazines. Generally, competitive cyclists use extreme positions that are lower than what you'll prefer. Other than that, though, the body position should be very similar, so you can compare.
If you think something's wrong with the reach on your bike, but you're not sure how to proceed, give us a call. We're fit experts and we can help.