Stem the Flow with a Stranglehold

Stem the Flow with a Stranglehold

 
Say the word "stem", and what do you think of?  Most likely, you did not think of a short tube with bolts attached that link a bike's handlebars to the forks.  

Flowers have stems. Stem cells can grow to become any one of the many tyoes of specialised cells in your body.
You can stem the flow of water from a pipe. WIne glasses have stems (do you hold the glass or the stem?  By the stem - that is why it is there.  So that you do not leave greasy finger prints, and so the heat of your hand does not warm the wine.  Now you know!). 
And, another bit of trivia, potatoes are actually high-modified plant stems, and the eyes are vestigial leaf buds.  But, a bike?

Let's face it - most parts on a bike are named with a remarkable lack of imagination.  Handlebars are bars for your hands.  Gears are, well, gears.  Derailleurs derail.  Cranks crank, and forks are, well, forked.  You get the idea.  But, stem?  The origin goes back to the form known as the quill, which predates the modern perpendicular-I tube unit.

One of the overlooked moving parts of a bike is the front fork unit.  The steering tube (the non-forked end) passes through the head tube (the front, near vertical part of the bike frame), and is held in place by the head set.  The challenge comes with how to attach the perpendicular handlebars to the top of the steering tube.


The classic quill stem is a single L-shaped unit that, inverted, slips into the top of the steering tube, with a tension bolt running down the centre of the stem.  When the bolt is tightened from the top of the stem is draws an oblique-cut block upwards into the base of the stem tube, tightening the fit against the inside of the steering tube.  The handlebars typically slip in to a broken-ring welded to the end of the quill, and held in place by a single closing bolt.

Although still popular with many bikes, the quill stem is mainly relegated to mountain bikes and commuters.  Road bikes tend to favour the threadless stem.  A simple tube with half-tubes welded to each end, offset from each other by 90°, one end is bolted to the top of the steering tube, and the handlebars to the other end, using half-round face plates to enclose each tube.

The beauty of this system is that it is readliy interchangeable with other stems, and can be manufactured in any length and angle.  You can also use an adjustable stem, with lockable pivots built into the stem, and telescoping sections to also adjust the length, although the adjustable stems do weigh much more than the carbon stems that are, unsurprisingly, found at the top end of the market.

Rather than buy a heavy adjustable stem, the issue becomes primarily what length.  And this is where things get interesting.

The stem holds the handlebars forward of the steering tube, so becomes an integral part of the bike's geometry.  Most people think of bike fit as being buying a bike that says Small-Medium-Large, ride it and see if it is comfortable or not.  

The further you ride, the more important it is that your bike is not only the right size, but that the adjustable parts are set up for your own unique geometry.  Seat height, seat position (how far forward or back), handlebar height (set by the riser rings beneath the stem), stem length.  Even the position of the cleats under your shoes affect how you ride.  There is no single best-fit, as different frames have subtly different tube lengths and angles.  



As far as the stem is concerned, this controls the reach - how far you have to reach forward to hold the bars.  Having a long body and short arms can be the same set-up as a short body and long arms, although the angle your body forms will be flatter with the long body option.  You could have long legs, requiring a longer down tube in the frame, but with shorter body and arms need a shorter stem.

There are websites that will calculate your ideal fit.  The site I used is 

http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

Note the handlebar extension length.  This is the stem.

Following the detailed, and photographic instructions, my wife and I worked through a series of body measurements, and entered them into the website form, which then gave the ideal measurement ranges for three different bike set-ups, each for a different riding style.  Opting for the "Eddy Fit", not because of its name (although that is a less than subtle factor in my own psyche) but for the description of the riding style.  My recommended stem length was in the range of 10.5 to 11.1 cm. 

As with many other bike parts, there is a premium on weight and materials.  Steel is cheap and heavy, carbon is expensive and is light.  in between are the alloy stems, of different alloy grades, tube thicknesses and lengths.  The deals that I found included a budget NZ$24 for a stem weighing 160 gm, but the best deal I could find was from the eBay trader superbicycle.shop, a stem from the Uno brand.  11.0 cm long, 114 gm weight for a total of NZ$41.24.  Here it is...

Of note is that the average $:gm ratio was NZ$0.27/gm weight, although this ratio increases as the stem weight goes down, giving a unit ratio of NZ$0.36 for the uno stem.  The 160 gm stem mentioned had a ratio of NZ$0.15, indicating the relationship between weight and price.  To see this, I created a scatter plot of the weight and price data, which shows the distinctly negative relationship.  As always, you get what you pay for.

Still, pay attention to your comfort, and utilise the ease with which the threadless stems can be replaced.  If you have recurring shoulder or back pain, get pain in your hands, or even if they go numb, try swapping out the stem for one of a different length, as this has a direct control over the degree of forward lean in your riding position and the degree to which your arms and hands support your weight.