Stem Length and Frame Size

We recently received our first shipment of 110 mm-long Grand Bois stems. The fillet-brazed stems are available in 10 mm increments from 60 to 110 mm. Now riders of all sizes can use these beautifully crafted, super-strong stems and decaleurs.

Some people may wonder about the shorter stems: Few modern bike makers specify stems shorter than 80 mm. However, for a small bike, it makes sense to shorten the stem, especially if you plan to use a handlebar bag.

In the drawings above, you can see how a 7 cm stem on a 49 cm frame places the handlebars in the same position as a 10 cm stem on a 58 cm frame, relative to the fork crown and front wheel. Therefore, a handlebar bag will sit on the rack in the same position.

No matter how tall your frame, your front rack always sits in the same place ahead of the fork crown. On the small frame, a long stem would push the bag too far forward, which would compromise the bike’s handling.

Beyond handlebar bags, there are other reasons to vary stem length over a greater range. Using a long stem on a small bike shifts the rider’s weight forward. To avoid toe overlap, many small frames have steep seat tube angles, which further reduces the weight on the rear wheel. This means that many small bike have much more weight on the front wheel than larger bikes typically do, and that probably affects the bike’s handling. A better way to avoid toe overlap is to shorten the stem and lengthen the top tube. The seat tube angle can remain almost the same as on a taller frame.

However, the stem length also affects the bike’s steering. A shorter stem changes the arc through which the handlebars swing. The effect is most pronounced “on the tops” near the stem, where your reach is determined solely by the stem length. “On the hoods” and “in the drops,” your hands are further from the steering axis, and the impact of stem length is less pronounced.

As everything in bicycle design, stem length is determined by a number of considerations. Different builders and riders weigh these factors differently, and thus design their bikes differently. Grand Bois now offers stem lengths that should suit most cyclists.

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into the high-performance components we need for our adventures.
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12 Responses to Stem Length and Frame Size

  1. djconnel says:

    When I’ve run simple numbers, I’ve not found that weight distribution is that sensitive to differences in stem versus top tube length. For example, a 1 cm shorter top tube with a corresponding 1 cm smaller front center will change weight distribution on a 100 cm wheelbase by around 0.5% absolute (for example, from 45% to 45.5% on the front wheel). Even small differences in body position can have as large an effect.

    But with wheel and contact point positions fixed, a longer top tube will steepen the head tube which will reduce trail. Many small frames have head tube angles in the 71 degree range, which results in a lot of trail, with 7 cm not being unusual. A shorter stem therefore, for the same fork rake, allows a steeper front end which will quicken handling. I wish I could make this change to my racing frame, which with its slack head tube changes heading at best reluctantly.

    • By itself, the stem length doesn’t change the weight distribution by much, but if you also steepen the seat tube, it becomes significant.

      70 mm trail on a small frame probably results from the fact that the company did not want to change the fork offset for different frame sizes. (That way, they could bend all fork blades the same.) Instead of slackening the head tube that much, they could have split the difference and increased the fork offset. The result would have been the same front-center as the 70-mm-trail bike, yet with a trail figure like that of the larger frames.

      For example, a bike with a 73° head angle and 55 mm fork offset has 48 mm trail.
      If you need more front center, you can reduce the head angle to 72°, increase the fork offset to 61 mm, and still end up with 48 mm trail, but a significantly longer front-center. Both bikes will handle very similarly.

  2. Dave Cramer says:

    I recently ordered a 650B randonneuring bike. The bike was designed around a 9cm stem, which I found interesting as the bike size is in the middle of the range (57.5cm top tube). In the racing-influenced community, it seems hardly anyone would have a stem shorter than 12cm.

    • Frank says:

      I suppose the longer stems in the racing crowd are related to their handlebars: Usually these have a shorter reach than the bars prefered by randonneurs, for example the Grand Bois handlebars or Nitto Noodles. The latter bars probably put the brake hoods too far forward to reach comfortably when used with long stems.

  3. marmotte says:

    I suppose it’s more about the fad of riding on frames really to small for your measurements, in order to achive a low riding position with superelevations of 12 cm and more.You then need a long stem to position your handlebars correctly. Not very comfortable for your everyday rider.

    The reach of your handlebars is of course another factor to take into account.

  4. Adrian says:

    “A better way to avoid toe overlap is to shorten the stem and lengthen the top tube.” What you mean here is that the front center should be lengthened, no? The longer top tube is just a dimension that might be caused by a longer front center (assuming offset, head angle are constant).

    • As you note, the front-center dimension (length from crank spindle to front axle) determines whether a bike has toe overlap. Lengthening front-center reduces toe overlap. (Making the wheels smaller is another way to reduce toe overlap while keeping front-center the same.)

  5. cept says:

    I wish these grand bois stems were 26.0mm to cover a wider range of bars. for 25.4mm, just add a shim.

    • When faced with a choice of clamp diameters, Grand Bois decided to make the stems to match their handlebars.

      • Greg says:

        I wish their bars and stems were both 26.0!

        I am becoming increasingly concerned that 26.0 may disappear at some point. With the silly oversized diameter now becoming popular (to match the silly oversized headsets that are inappropriate and unnecessary for road bikes), and with 25.4 being used for track applications (plus ‘low-end’ bars), I can sadly envision a day when 26.0 is no longer available. .

  6. mike says:

    the shortest stem offered by Grand Bois (and all other makers that I’ve encountered) is 6cm. I have a bike which I love but it’s long in the top tube and I am wondering if there is any reason why a stem shorter than 6cm isn’t made or shouldn’t be used.

    • There is no obvious reason why a very short stem cannot be used. Swept-back handlebars place your hands in the same position as a very short, zero-length or even negative-length stem.

      Finding a stem shorter than 60 mm may be hard. An alternative is raising the handlebars, which reduces the reach, as the bars go back and upward toward you. (This is assuming your handlebars are lower than the saddle.) Or you could use swept-back handlebars that dramatically decrease your reach. (You may need to use a longer stem with those.)

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