The bike's stem is an extremely important part on your bike, whether road bike, mountain bike, trekking bike, E-bike or children's bike. It connects the handlebar with the rest of the bike and the sitting posture can be significantly changed by means of different lengths and angles.
Attention should be paid to the fact that there are four parameters for a stem:
- Diameter of the steerer tube
- Diameter of the handlebar clamp area
- Length and
We distinguish 3 stem types:
Older variants: Stems with expanding cone
Stems with expanding cone or inclined cone are inserted into the steerer tube. They provide the advantage that the height of the handlebar can be continuously adjusted and the stem demounted without having to loosen the bearing system of the headset. The height adjustment of a quill stem is very easy: The stem can be pulled out without having to loosen the bearing system of the headset. That is exactly what can result in problems, the lever forces (bend) become too high, the material of the tube is overstrained, will wear out and can break off directly above the headset! These stems are hardly ever used nowadays.
Ahead stems are stems that encompass the fork's steerer tube from the outside and which are clamped with screws. Precondition: It must be a fork steerer without external thread.
The height adjustability of the handlebar is more laborious than it is with quill stems (expanding cone) and can only be achieved via spacers if the fork steerer is sufficiently long. In order to further change the sitting posture beyond that, you can get stems in different lengths and angles. The advantage in this case is a significantly stiffer connection between the handlebar and the fork!
Direct mount stems
This stem is standard with downhill bikes. The stem only fits on double crown suspension forks since it does not have any contact to the fork steerer but is bolted onto the upper crown or it is already included in the crown as a standard, which means that the crown and the stem are one part. The advantage is quite clear: The direct mount stem is significantly stiffer than the ahead one.