How does stem length affect a bike’s steering and handling?
Today’s marketplace provides a wide variety of stem lengths and angles, allowing riders enormous flexibility for fine-tuning their reach to the handlebars. While comfort and an effective position trumps all other considerations, Matt Wikstrom takes a closer look at the influence of stem length on the steering and handling of a road bike.
Almost since the invention of the safety bicycle, the handlebar stem has served as a crucial point of adjustment. While the earliest designs offered negligible reach, longer, adjustable versions soon emerged.
Marshall “Major” Taylor is credited with the invention of the first adjustable bicycle stem at the close of the 19th century. The design employed a sliding clamp on a protruding length: the handlebars could thus be adjusted fore and aft to suit the size of the rider. Taylor used the stem to great effect, winning a multitude of races, first in the US and then throughout Europe.
Taylor’s “outrigger” eventually gave way to sturdier one-piece designs and ever since then riders have adjusted their handlebar reach by fitting stems of different lengths. Nowadays, there is a choice of stems as short as 50mm and as long 150mm with a variety of angles for fine-tuning the position of the handlebars.
Such adjustability allows a rider to consider a variety of frame sizes and geometries, especially when selecting the parts for a custom road bike build. But the question arises: can a stem be too long or too short for a bike? And is there an ideal length?
No simple formula
Custom framebuilders are perhaps the best source of information on the matter of stem length. After all, they are in the business of building bikes that provide an ideal fit for their clients, and part of that process involves determining the best stem length for each frame they build.
When I put the question of stem length to Steven Ledoux of Jaegher in Belgium he said, “We try to keep stem length within certain margins in relation to the frame size to keep a nice balance handling wise. Compensating a wrong frame length by mounting a short or very long stem is never a good idea.”
Richard Craddock of Craddock Cycles based in the UK expressed a similar view, “In general I find the best balance is a medium length stem. Of course, all this depends on your position and whether you have a frame with the right top tube length to allow you to achieve that position with a medium length stem.”
For Tom Kellogg of Spectrum Cycles in the US, one of the most important considerations is the rider’s reach, which he refers to as ‘cockpit length’.
“It comes down to the cockpit length not rider height. Longer cockpit riders should have longer stem/bar reach combinations,” Kellogg said. “And the more aggressively a bike will be ridden, the (somewhat) longer the stem. Full on race bikes should have longer stems than touring bikes, all other things being equal, in order to get more weight on the front wheel.”
The importance of the bike’s purpose is something that also stands out for Ryan Moody at Baum Cycles. “Stem length will vary with the design of the bike. It must also address the rider’s comfort, biomechanics, performance needs, and the steering and handling of the bike. Deciding on the best stem length depends on the rider’s priorities for each because a relaxed position compromises performance, and it’s not always possible to achieve ideal biomechanics.”
Clearly, there is no simple formula for determining stem length and the solution is highly individual. However, there are two considerations that are worth discussing because they will affect every rider.
To simplify matters, let’s consider a bike that has an adjustable front end that allows the overall reach to the handlebars to be kept constant as different stem lengths are fitted. In this circumstance, stem length dictates how much weight is placed on the front wheel.
“The longer the stem,” explains Tom Kellogg, “the more the rider’s weight pushing forward on the bars tends to keep the front wheel pointing forward.” As a consequence, the bike becomes more stable, especially at high speeds, which accounts to some extent why pro riders normally opt for a shorter frame and a longer stem. The extra stability also helps with the control of high profile race wheels in windy conditions.
Another important consideration is where the weight is placed, as shown in the figure below:
Ideally, the rider’s weight needs to be as close as possible to the contact patch of the front wheel. “A very short stem with a long top tube can leave the front wheel feeling a little light,” says Richard Craddock. Ryan Moody agrees, adding, “Weight behind the front wheel’s contact patch produces vague handling but there can be too much weight over the front wheel as well.”
The other consideration for stem length is the effect it has on the size of the steering arc, as shown in the figure below:
As Tom Kellogg explains, “Short stems steer more like a steering wheel while long stems steer more like a tiller.” For Ryan Moody, he sees it in terms of the ratio of input to output. “Short stems provide a more immediate response but they are susceptible to smaller movements of the body, which translates into twitchiness.”
Richard Craddock is cautious about long stems though. “A very long stem with a short top tube can slow the handling. If a rider’s hands are very far ahead of the steering axis it can be harder to steer at low speeds.”
Ultimately, the steering of a bike is dictated by its head angle and trail—not stem length—but the stem can enhance or dull it to some degree. Thus, a short stem will make a bike with quick steering more nervous while a long stem will act to calm it down. In contrast, a long stem may slow down the steering too much if the bike has a relaxed head angle.
Stem lengths for women
While I was speaking with Ryan Moody, he highlighted one special consideration for stem length: “Women typically need short stems to suit their short torsos. A short torso limits the amount of weight that can be put on the front wheel. We can shorten the frame to some degree but toe overlap limits how close the front wheel can be positioned under the body.”
It’s a problem that Richard Craddock has also had to contend with. “Some brands just reduce the head angle to move the front wheel away from the toes to avoid overlap. This gives a higher trail figure, more flop and odd handling as the fork offset is generally not changed to suit. It’s better to design for a short stem in this case to keep good steering characteristics with a sensible head angle.”
Summary and Conclusions
In most instances, riders don’t have the freedom to elect their stem length, and instead, vary it to fine-tune their position on the bike. I have no argument with that strategy, however when deciding on a frame size or comparing frames with different geometries, it is worth contemplating the final stem length that will be required by each.
Ideally, the stem should be long enough to place some of the rider’s weight over the front wheel to stabilise the steering and improve grip on the road. At the same time, the stem should provide a steering arc that complements the head angle and trail of the bike.
While it is difficult to make a firm recommendation, longer stems are generally better suited to road bikes because the rider is more likely to be travelling at high speeds, and therefore, more likely to benefit from (and appreciate) the extra stability they offer. To put a (rough) number to it, a long stem is 100-120mm, very long stems are 130mm or more, and anything less than 90mm can be considered a short stem.
When viewed in the context of the entire bike, the influence of stem length is relatively minor. Most riders will quickly adapt to any stem length as long as it serves the reach they need. That said, finding a rider’s ideal stem length promises to refine — even perfect — the quality of their bike’s steering and handling.