I could see the hazard down the trail: a tree root followed immediately by an off-camber, hairpin curve. I thought I could handle it, but I couldn’t orchestrate two opposite movements with my handlebars in such quick succession. Halfway into the turn I knew I’d never make it, so I threw on my brakes.
Thus, instead of skidding off the hillside, my braking made me fly off over my handlebars.
Leaving aside rider error, one change in my bike geometry could have dramatically improved (maybe even eliminated): a shorter stem.
Maybe you’re wondering: What is a stem and how would changing it have made a difference in me going head-over-handlebars?
What is a mountain bike stem and what does a bike stem do?
The simple definition of a mountain bike stem is that it’s the part of the bike that connects the handlebars with the steerer tube. This connection can be threadless, using a clamp, or a threaded stem with a quill headset. To learn more about stem styles, read this.
But functionally, the mountain bike stem is much more significant than just being a connecting piece. In terms of impacting your riding, the mountain bike stem does two things:
- Affects the way your body fits on the bike and where your weight is distributed.
- Affects the responsiveness of the steering.
If you’re feeling cramped on your mountain bike, your first response might be to switch to a longer stem to extend your torso farther from the seat. Conversely, if your shoulders and arms are overextended, leading to muscle strain and exhaustion beyond the rigors of your riding, it might make sense to switch to a shorter stem.
DIY MTB Tip: Does your bike stem affect how strong you are on a bike? I’d say yes. Read about how your comfort will make you a better rider. Different Ways to Make Your MTB More Comfortable
However, before you implement either of these changes, read on to understand how changing the stem will impact your mountain bike handling. Considerations like your preferred type of riding and expectations for bike handling are just as important (or more) when choosing the length of a mountain bike stem.
Attributes of short mountain bike stems
Short mountain bike stems allow for faster turning of the handlebars which equals more responsive steering. Shorter stems are preferable for downhill and enduro riding because of the need for quick steering at fast speeds.
My personal example in the first paragraph is a prime example. Additionally, shorter stems position your weight farther back on the bike which is superior for descents and also more aerodynamic. Another added benefit is that you’re less likely to fly over the handlebars!
A shorter mountain bike stem is in the range of 40mm to 80mm. Though much depends on personal preference, downhill riders usually opt for the shorter end of the range (40-50mm), while enduro riders tend towards the middle to upper end of the range (50-80mm).
There are some “ultra short” stems on the market. While it may seem tempting to go for the shortest stem available (if you’re a speed demon who loves bombing down descents), it’s not advisable for stems to be shorter than 25mm.
In general, a shorter mountain bike stem is usually paired with narrower handlebars (680mm – 740mm).
Attributes of long mountain bike stems
Longer mountain bike stems pull your weight farther toward the front of the bike. With your weight positioned more over the front wheel, the mountain bike steering is less quick. However, it improves the efficiency of your pedaling. And, your body is in a better position for climbing. After all, there’s a reason spin classes have you leaning on the handlebars so much!
Longer stems, in the range of 80 to 150mm, are better for cross-country riding. Riders with longer stems typically prefer using wider handlebars (760mm – 800mm).
How do you measure stem length?
To measure stem length, measure from the center of the headset to the center of the handlebars. Since bike components, including bike stems are measured in millimeters, you can convert from inches by multiplying your measurement by 2.54 if your ruler only shows inches.
Two other steering considerations: Stem rise (or angle) and handlebar sweep (aka “handlebar drop”)
Stem rise is the angle of the stem in relation to the steerer tube, so it determines how far above or below your handlebars are from the stem. Rise is less important with shorter stems but worth considering with longer stems.
Again, the optimal level of handlebar rise (or drop) is determined by the type of riding you do. Downhill riding is better with the handlebars level, with no rise or drop at all. This is known as a 0-degree rise. Meanwhile, enduro and trail riders usually choose a slight rise, between zero and six degrees. Conversely, cross-country riders typically prefer a drop of zero to 30 degrees.
Another element to consider when deciding on an optimal stem height is the sweep of your handlebars. Some handlebars are more or less a straight line from left to right. Others resemble bull’s horns – straight in middle and sweeping upward on each side. And the rest are some variation between these two extremes.
The more dramatic the sweep, the more handlebars can effectively change stem length. If your handlebars have a dramatic sweep and you angle them down, this can have the same effect as a shorter stem. Vice versa, angling the handlebars up can have almost the same effect as using a longer stem.
Know your body geometry when choosing stem length
I mentioned before that changing the stem length is often an easy go-to for resolving issues of a bike frame that essentially feels to big or to small, without replacing the mountain bike or making extensive modifications. While it’s certainly an option, the resulting changes to bike handling mean it should be used as a last resort.
Bikes are designed with the assumption that the rider’s body is perfectly proportionate. However, few of us really match that standard. For example, my torso and legs are roughly equal, contrary to the typical longer-legged female body that women’s specific mountain bikes are designed for.
Things to consider
However, it’s not a drastic enough deviation from normal to require any special changes for my bike to fit me. Alternatively, my husband has legs that are wildly long in comparison to his torso. A shorter stem suits his physical geometry – as well as his penchant for blasting down hills.
Knowing your body proportions, as well as any specific medical/orthopedic conditions, is also useful to factor into considering stem length.
DIY MTB Tip: Stems, Handlebars, Saddles – Putting all of this together can be tough. Read about ow to get you handlebars to fit in this article: How to Make Mountain Bike Handlebars More Comfortable
How do you choose your stem length?
How to choose the right stem length depends on a variety of factors specific to you. To begin with, examine what is prompting you to want a change. Is it physical discomfort? Maybe your neck is sore from having your arms too far in front of you during rides and you think a shorter stem might ease that. Or, maybe you don’t like feeling like your torso is below your body and think a longer stem would lift your handlebars up more.
If you’re coming at the issue of stem height because of physical motivators, it’s important to factor in the impact any changes will have on your riding. Recognize that going shorter with the stem will make the steering quicker and snappier.
Your style of riding
So, will that change suit the type of riding you do? If you’re already feeling frustrated with how slow your steering is, then switching to a shorter stem might solve two problems for you.
If you want to switch your stem to change your riding, then the decision may be a little easier. If you want faster steering for downhill riding, go with a shorter stem. If you’re a cross-country rider who loves challenging climbs, go for a longer stem in order to get more power out of your pedaling.
Conversely, if you love downhill riding but feel cramped on your bike, switching to a longer stem might resolve your physical discomfort while decreasing your maneuverability. That may not be a worthwhile trade-off.
Additionally, modifications or repositioning of other parts of the bike may have the same desired effect as swapping out the stem. For example, adding or removing spacers on the headset will essentially lengthen or shorten your stem – and save you the expense of buying a whole new part.
Reach – Saddle to bars
Another example is sliding the saddle forward or backwards on the rails. This brings you closer or farther away from your handlebar, which may help you find a better distribution of weight on the bike or lengthen your torso in a more comfortable position between seat and handlebars.
Switching stem length often requires balancing priorities and considering the trade-offs. Are you willing to accept the way the shorter stem changes your physical dynamic in exchange for faster steering? Can your neck and shoulders handle the longer stem in order to have more powerful climbing? Those are questions you’ll need to weigh personally.
When to change your bike stem and why
But for me, the decision of switching to a shorter stem was clear. I’d never had the problem of feeling cramped on my bike – quite the opposite, actually. And, after flying over the handlebars during a maneuver I really thought I could handle, I didn’t spend any more time wondering. I switched to a shorter stem and have never regretted it.
Learn more about Pedals, Handlebars and Brakes
- Handlebars on MTBs are wide, find out why – Why are MTB Handlebars so Wide?
- Should you upgrade your handlebars? Read – Are Handlebars Worth Upgrading?
- Universal pedals? Read all about it here – 9 Universal Pedals for Your MTB
- Learning how to Jump? Learn more with – How to Jump a MTB with Flat Pedals
- Keep your disc brakes clean – How to Clean Mountain Bike Disc Brakes
- Is their a difference? – Mountain Bike V-Brakes vs Disc
Professional writer Kat Jahnigen was 2 miles from the nearest village – and roughly 2,310 miles – from the nearest English-speaking town – when her bike tire burst. At that time, she was a college student on a bike trip across the desolate, rocky island of Crete. It suddenly occurred to her that it would’ve been good to learn some basic bike repairs before setting off on a solo bike trip.
Check out Kat’s website WriteHire at writehire.net.