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Bicycle Frame Geometry: Stem Length

Recently, I discussed the how head tube angle, fork rake, and trail effect the steering characteristics of a bicycle. Hopefully that article was more enlightening that baffling. With that less than straight forward aspect of frame design covered, let’s move on to something seemingly more straight forward: stem length.

Frame sizing: Sloping Top Tubes

Back when the majority of bikes were made of lugged steel, manufacturers offered a wide array of sizing options for cyclists. While it made for an exact fit for the end user, it was an expensive undertaking for the manufacturer. A quick look at the 1991 Eddy Merckx catalog reveals that they offered bikes in 1 cm intervals from sizes 47 cm to 64 cm. That’s eighteen sizes!

In the late 1990s, the advent of sloping top tubes allowed the frame manufacturers to cut down on production costs significantly. Sizes went from a number, to size. Fit was to be determined by stem length and saddle setback. This has allowed big bike manufacturers to half the number of sizes offered. The norm these days is between 7 and 9 sizes, depending on the brand. 

The Effects of Stem Length

All the major bike brands I can think of use the modern model for bike sizing. With this in mind, we now use adjustable components like seat posts and stems to dial in fit. So how does that affect the handling dynamics of a bike? It depends on how you size a bike.

Smaller Frame Longer Stem

When it comes to modern bikes, I personally fall in between sizes. I choose to ride a slightly smaller road bike with a longer stem. The advantages a smaller bike offers are lighter weight, higher stiffness, and a shorter wheelbase. At 130mm, I am running what is considered a long stem.

Due to running a long stem, the dynamics of the bike are changed somewhat. The longer stem gives me an aggressive riding position. This puts more weight over the front wheel and a gives wider turning arc. This combination offered by the longer stem slows the steering somewhat, but also adds a bit of stability.

Larger Frame Shorter Stem

There is also the option that many distance riders choose, and that is a larger frame with a shorter stem. Larger frames give riders a compliant ride, less aggressive positioning, and better steering a low speeds. This is great for long distance riders and those who ride at a more leisurely pace. 

While a long, slammed stem certainly looks good on a race bike, it’s practical application is not for everybody. The way bikes are sized these days still gives riders options depending on the type of riding they enjoy doing. The key is to get the right fit for the right bike. Stay safe out there, and as always, keep the rubber side down!

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