Hydration Systems

There are two main styles of stems - threaded style and threadless style. For the older threaded style, the stem is inserted INSIDE the fork's steerer tube and secured with a wedge. With the newer threadless style, the stem slips over the OUTSIDE of the fork's steerer. All modern mountain bikes and many road bikes use the threadless setup. Many dealers sell only the newer style threadless stems and compatible threadless headsets and forks.

When shopping for a threadless style stem, you must consider 4 measurements (Fig. 1) - the diameter of the stem clamp (A), the diameter of the handlebar clamp (B), the length of the stem extension (C), and the angle of the extension (D).

Fig. 1 - Important Stem Measurements

Most important is the stem clamp diameter (A). The stem clamp on a threadless stem is one of 3 sizes: 1", 1 1/8", or 1 1/4". By far, the most common size is 1 1/8", used on almost all mountain bikes and many road bikes. Some road bikes use 1". Finally, 1 1/4" is used by a few rare mountain bikes.

Stem Clamp Diameter (A)

Measure the outside diameter of the fork's steerer or the inside diameter of the stem. Use the following table to convert the size you measured on your bike to the actual size to order.

Stem interior diameter / fork outer diameter	Stem/Headset/Fork size to order
1 inch or 25.4 mm	1"
1 1/8" or 28.6 mm	1 1/8"
1 1/4" 31.8 mm	1 1/4"

Handlebar clamp diameter (B)

Virtually all mountain bike stems use the same handlebar clamp diameter, thus, any mountain bike stem can usually be used with any mountain bike handlebar.

Road bike stems and handlebars can vary slightly. The most common size for the handlebar clamp is 26.0 mm, although 26.4 is also common. When in doubt, measure your equipment to be certain prior to ordering.

Stem Extension Length (C)

The stem extension (along with the extension angle) determines the reach of the bike - how far you must reach to grasp the handlebars, brakes, and shifters. If you're happy with the fit of your bike, simply measure your existing stem and order the same size. Ordering a slightly longer or shorter stem will change the fit of your bike, either putting you in a more aerodynamic, aggresive position or upright, relaxed position respectively.

Extension Angle (D)

The extension angle of the stem is purely a matter of comfort. Choose any angle you like. A comfort-oriented rider may prefer a stem with a bit of rise, while more aggresive riders would probably prefer a flatter, lower stem.

Some info sourced from our affiliate partner: Jensonusa