Stems are prepared in various lengths and for various handlebar diameters. They are one of the few ways to alter wheel geometry and sitting position after the fact. The bike stem is affixed to the steer tube over the head tube, gripping the handlebar. It consists of either carbon or aluminum. With the first one, the rider must pay careful attention to the tightening torque. Special mounting paste is recommended for use with carbon parts.
Handlebars and stability
Stems are designed for specific classes of bikes. This is reflected in their strength properties and weight. What's more, different standards have developed for different kinds of bikes. For example, the thicker 35mm standard for mountain bikes is quite recent. It allows thicker and more stable handlebars for the enduro discipline. Riders shouldn't exchange road bike components for stable cyclocross bike parts. The latter are intended for use on terrain. The former are sufficient for use on roads.
Influence on steering behavior
The length of the stem influences the leverage forces that operate while turning. If you change the bike's stem, the force relations between the hub and handlebar change as well. In principle, its length should have a sound relation to the head angle of the headtube. This way, drivability won't be negatively affected. Trekking bike stems with built-in adjustability are available, the angle can be altered. As for MTBs, the shorter the stem is, the more immediate the turning behavior is. One disadvantage: There is less pressure on the front wheel. A test run pays off. RaceFace has a wide variety of high-quality attachment parts!