Getting your handlebar height right is essential if you’re going to be comfortable and fast on your road bike: too low and you could suffer from back and leg pain; too high and you’re going to be wasting unnecessary energy overcoming wind resistance caused by sitting in a more upright position.
The good news is that if you do decide that you need to change your handlebar height and need to adjust it to improve either your comfort or your average speed, then the process is dead easy.
Depending on the make of your bike, you will either need an Allen key of a Torx key to first loosen the stem bolts, and then to remove the headset cap.
Stem and headset cap out of the way, you are free to add or remove spacer in order to position the stem at the correct height. If you’re after the pro look then you can completely remove all the spacers, or at the other end of the spectrum you could have up to 3cm of spacers below the stem.
Once you’ve got the stem at the correct height, reattach the headset cap and then retighten the stem bolts using a torque wrench, making sure that there is no play and that the handlebars are lined up straight with the front wheel.