Adjusting a Bicycle
From the feet, adjustment moves to the saddle. If you think about the motion of your leg during each pedal stroke, you'll quickly understand why saddle height is so important. At the bottom of each stroke, your knee is almost straight, but at the top it's bent fairly sharply. The higher the seat, the less bend there is in the leg, and the less knee stress there is on the down stroke.
When you bought the bicycle, the shop should have helped you find approximately the right saddle position, but this is an adjustment where millimeters count, and it's going to take some fine-tuning to get it right. There is no consensus on ideal seat position. The only thing most experts seem to agree on is that many cyclists ride with their saddles too low. And within limits, too low is worse than too high.
You want to set your seat high, but not so high it hyperextends the knee at the bottom of the pedal stroke or robs you of power because your feet lose contact with the pedals.
Finding the Right Height
Sit normally on the bicycle with someone holding it upright to help you balance. Put your feet in the toe clips or clip-in pedals, and pedal backward until your foot reaches the bottom. Racers, who draw power from calves and ankles as well as thighs, will tend to have their toes pointing downward at this point. Recreational cyclists are more likely to have their feet closer to level. Regardless, your knee should be slightly bent. If it's locked, you're too high. Adjust the seat accordingly.
What matters is putting the foot in the same position you'll be using on the road. If that changes as you gain experience, you can always readjust your seat height.
Another approach is to take the bike out on the road or put it on an exercise stand. Pedal, while another cyclist watches you from behind. If your pelvis rocks back and forth, your seat is too high, forcing you to reach for the pedal at the bottom of each stroke. Lower it to the point slightly below the one at which you start to rock.
A third, time-tested approach is to pedal backward with your heels on the pedals, adjusting the seat until you find the maximum height at which your feet maintain easy contact with the pedals, all the way around.
These three approaches probably won't give you the same result. Try them all, and since too low is worse than too high, pick a height near the upper end of the resulting range. If you feel twinges of knee pain on your first excursions after a change in saddle height, adjust the seat by a couple of millimeters (probably upward), and see if they go away.
You might think that once you get your seat properly adjusted, you'll never need to change it. But that just isn't the case. Buying a new pair of shoes with a different sole thickness will require a change in seat height, as will purchasing a new saddle. And some days, the height you've always used just seems inexplicably wrong.
Making the Adjustment
Adjusting seat height is a 30-second job, faster if your bike, like some mountain bikes, has a quick-release lever on the seat post. Loosen the seat post (either with the quick release lever or an Allen nut at the top of the seat tube), pull the seat up or down as needed, and tighten it again. Work in small increments; for fine-tuning, one quarter of an inch is a big change. To keep from losing track of your starting point, mark it with tape or by lightly scratching the seat post.
Whatever you do, don't exceed the maximum safe-height line inscribed on the seat post. Look for this line the first time you adjust your saddle height so you're sure you know what to look for. If you need to go higher than that, get a longer seat post.
When adjusting saddle height, wear your cycling shoes, and if you're planning on buying a gel seat cover, mount it first. Otherwise, you'll have to adjust the saddle all over again.
Details mentioned in this article were accurate at the time of publication