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Define stem mounting8/18/2023 I suppose that “ Alloy” refers to “aluminium alloy.” The last info is about the stem’s angle (15 degrees), handlebar gripping diameter (repeated here?), and it would make sense to provide length in mm, but it says “Rise:” – no idea why. – For details see the handlebar dimension standards.Ĥ. Handlebar width – the part where grips and levers are mounted is 22.2 mm (standard MTB handlebars). Stem’s handlebar clamp is the “oversized” – 1 1/4″ (or 31.8, or 31.7 mm – depending on how one rounds the 1 1/4″ to mm).ģ. Fork steering column outer diameter (and stem’s inner diameter, where it clamps the steering column) is 1 1/8″ (28.6 mm).Ģ. Some guessing – since it’s not written clearly enough for me to understand (maybe someone else can, but I can’t):ġ. Related post – Bicycle handlebar dimension standards: Bicycle handlebar dimension standards Categories Standards Steering column outer diameter (and inner diameter for the attachment on the stem) Standard for most threaded forks with an outer diameter of 28.6 mm (1 1/8″) – not very common Standard for most threaded forks with an outer diameter of 25.4 mm (1″) Stem “neck” outer diameter – measurement units: mm (inches) Steering column attachment dimension standards 3.2.1. Obsoleteģ1.7 – 31.8 – depending on how manufacturers round down the inch dimension which is (1 1/4″)ģ.2. Standard ISO size, common for bars from the end of the 20th century Obsolete British standard common on old British 3-speeds Handlebar attachment diameter – measurement units: mm (inches) Handlebar clamp dimension standards TABLE 1 While the third one will show that for the quill stems. Second table will show threadless stems for attachment diameters. First table will show bar attachment diameter standard. Picture 5 shows how.Īfter dimensions were defined and their measurement explained, now an overview of the standard dimensions will be given. Of course, if a new stem is sought for a fork at hand, then the fork is measured. Steering column attachment diameterįor threadless stems, this is measured the same as the handlebar attachment diameter. One could also measure the (outer) bar diameter (at the stem attachment point) – if a new stem is sought to match the bars. Picture 3b doesn’t show clearly enough, but the calipers are placed at the inner side of the black part of the stem, just near the slit – there would be no use measuring at the slit itself, of course. Measurement method is shown in picture 3. This dimension is measured practically identically for all the stems. However, in terms of (attachment) standards, important dimensions are the handlebar attachment diameter and steering column attachment diameter. Lenghts and angles differ and are important when fitting a bicycle to suit a rider. Picture 2a shows a quill stem with a shorter neck, angled downwards, next to a threadless stem with a longer neck. Stems are made with various lengths and angles. It is fastened by sliding it onto the steering column, and then tightening the pinch bolt(s) that hold it fastened. Threadless stems have a slot at the steering column attachment end. Without much going into details and various designs, the basic principle is shown in picture 1. Quill stem is attached to the steering column by inserting it into the steering column and tightening a bolt on top of the stem, that pulls the quill upwards, making the lower stem diameter wider. There are two types of stems (in terms of standard attachment dimension): quill (for threaded forks) and threadless (a.k.a. The remainder of this post will explain stem types, important dimensions, how to measure them and, finally, list the dimension standards. Dimensions and type of steering column attachment depend on the fork, that is depended on the frame, so that’s something a bit harder to “change” – though, if choosing a frame, this author’s recommendation is to look for one with a 1 1/8″ steering column diameter and a threadless fork – for several reasons. If bars are not already owned (at hand), author’s recommendation (personal preference based on knowledge and experience) is to choose a stem with a modern OS (“oversized) bar attachment diameter ( table 1 lists the standard dimensions). Both the side of steering column attachment, as well as on the side where the bars are attached. When purchasing, or replacing a stem, it is important to know what type and what size is needed. Other dimensions, such as stem length and angle will be explained in a separate post. This post explains stem size standards in terms of steering column attachment and handlebar attachment at the opposite end of the stem. Steering column attachment dimension standards …3.2.1. Handlebar (clamp) attachment diameter 2.2. Important dimensions and how to measure 2.1.
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