My sister gave me the task of making her older Trek 4500 more comfortable. The bike is still in great shape and just needed some different components to give the bike a more “upright” riding position.
After looking at how the bike fit on her, I made the shopping list which included a new and different stem. I should digress a bit and describe – “What a stem is”
A bike stem (sometimes called goose neck) is the connection between the handle bars and steerer tube. Modern bikes use two styles of stem; Quill or Threadless Clamp-On. Quill stems clamp internally onto the threaded steerer tube. Clamp-On bolt onto the outside of a threadless steering tube. A bike stem affects bike fit, body position and steering sensitivity.
Styles of Bike Stems
Quill Stems for Threaded Headset
Also called a goose neck, were the most common type of stem for bikes. For the most part you only see quill stems on more inexpensive big box bikes and kids’ bikes. This stem must be used on a threaded headset which has fallen out of favor.
I would say that the quill style stem is unique in that it is easy to adjust the handlebar height for the rider. I’ve also found that the stem can be difficult to tighten, causing the steering linkage to come loose.
Threadless Clamp-On Stems
The clam-on style is the most popular style of stem on modern bikes. This system is stronger through the use of larger diameter tubes and less complicated.
Some fit flexibility is lost with threadless systems, but by purchasing some options a strong comfortable steering stem can be achieved.
As the name implies the stem “Clamps-On” the steering tube (sometimes called the steerer tube) with either 1 or 2 clamp bolts.
Stem Sizes, Angles and Dimensions
Threadless Clamp-On Stems
Diameter of the Stem, is usually the first number called out when looking at clamp-on stems. This defines the steering tube OUTSIDE diameter. Two common sizes are available; 25.4mm (1 inch) and 28.6mm (1 1/8 inch).
Both of these sizes are common, so if you’re shopping for a replacement, you’ve got to measure this. Also don’t confuse the handlebar diameter – usually 25.4 with the stem diameter.
A rare size 31.8mm (1 ¼ inch) is used on some downhill racing bikes.
DIY MTB TIP: Gap between top of stem and steering tube. Without gap it will be impossible to tighten the threadless headset assembly.
Stem Length, so now we get into the personal preferences for bike fit. The length or sometimes called the extension is how far the handlebar attachment extends beyond the steering tube. This measurement is from the center line of the steering tube to the center line of the handlebars.
A typical stem length dimension is 70-80mm. Sizes can range from short 35mm to over 130mm.
A longer stem length can shift the rider forward into a more aggressive riding position. The longer stem will slow the turning sensitivity as well.
Angle, is the “lift” the stem angles up from the steering tube. In my opinion the stem angle and handlebar “rise” are easy ways to shift the rider into a more upright position. The stem angle can be sloping down, a common road bike angle is ~73 degrees which levels stem.
It’s common for cruising bikes to have adjustable angle stems. These are great for casual riders, but not recommended for mountain biking or serious road riding.
I recently made a video on how to make a MTB more comfortable and I replaced the stem. Check it out below
Handlebar Diameter, the most common handlebar diameter sizes are 25.4mm (1 inch) and 31.8 (1 ¼ inch). I mention this because it’s easy to get this dimension mixed up with the steering tube diameter.
NOTE: some downhill specific MTBs are adopting even larger handlebar diameters for increased stiffness and lighter weight.
Folding Bike Stems, do you want to store your bike in a hallway, but the handlebars are too wide? You can get a FOLDING STEM. The stem has a releasing lock that allows the handlebars to be turned parallel to the bike frame. I found these on Amazon here’s a link to read more – THINstem FOLDING BIKE STEM
How Stem Angle and Handlebar Rise work together
Folks remember making quick height adjustments by loosening the wedge bolt and quickly raising the stem/handlebars. So, I’m often asked how can I raise my handlebars on a threadless clamp-on stem.
The solution is replacing the stem and/or handlebars. A stem with angle above 45 degrees and increased length positions the bar up and slightly away. Installing handlebars with a “rise” can move the hand position back toward the rider.
Any alternate solution is an adjustable angle stem with a length of over 90mm.
Both stem angle and length affect the bike fit, which can result in better peddling power transfer, more comfort and aerodynamics
Threadless Clamp-On Stem Torque Recommendations
Always consult your bikes specific owner’s manual for torques. I don’t mention torque for carbon handlebars as these require special joint compounds and the stem blocks must be inspected for burrs.
If the manual isn’t available here are my recommendations
|Location||Torque in-lbs or N-m|
|Stem Bolt M6 (2-bolts)||Max 130 in-lbs or 15 N-m|
|Handlebar M6 (2 and 4 Bolt)||120 to 140 in-lbs or 14-16 N-m|
DIY MTB TIP: If possible, when replacing or repairing a stem or fork, ADD spacers both below and above the stem. Of course, the steering tube needs to be long enough to do this, but having height adjustment flexibility is great.
Quill Stem Dimensions
Diameter, the most common size of quill stem is 22.2mm. You’ll find this on most bikes built before 1980. The 21.1mm was common years ago on BMX bikes. Now quill stems are mostly used on big box brands of inexpensive bikes.
Length, the stem length is measured from the center line of the steering tube attachment to the center line of the handle bars. The distance affects the rider reach. Since the stem length is set, fine tuning the reach is done with seat position.
The stem reach also plays a factor in how responsive the steering will be. A longer stem length is less responsive as compared to a shorter length.
Handlebar, nearly all modern mountain bike handlebars are 25.4mm (1 inch). Some custom and European bikes will have another dimension, but it’s rare.
Angle, stem angle affects the body position. A higher angle will “lift” the handlebars. Often on cruiser style or mountain bikes the stem angle will be between zero and 35 degrees.
Adjustable angle quill stems are available. This style of stem is very adjustable, as the insertion height of the stem can be adjusted along with angle.
Older road bikes with quill stems usually have a 73-degree stem angle, which levels the stem. Because the height of a quill stem can be adjusted quill stems but those bikes like most have moved to Common quill stem sizes are
Adjusting a Quill Stem
Adjusting the height of the handlebars and realign the handlebars to the tire is pretty simple. All you need is a 6mm hex wrench and a hammer.
The best way to detail is with this video I made.
Assembling a Threadless Clamp-On Stem
On threadless headsets a bike stem also performs the function of locking down the pressure for the steering tube. An important item is to understand that if the stem is tight on the steering tube you won’t be able to tighten the steering tube (compress) bearings.
- It’s a simple procedure, first loosely place the stem on the steering tube.
- The steering tube must be below the lip of the stem. If the steering tube is above the stem, remove the stem and install spacers.
- Make sure the stem clamp bolts are loose. The stem must be able to slide on the steering tbue.
- Place the stem cap on the stem.
- Guide the compression bolt through the cap and into the star nut.
- Tighten until you remove any slop between the bike frame and stem.
- Align the handlebars
- Tighten the stem clamp bolts to the specified torque.
Mountain Bike Tip: It’s always good to double check the handlebar alignment and steering tube slop after the bearings have had a chance to settle. Simple squeeze the front brakes and shift the bike forward and back feeling for movement described in step 6 above.
Below is a chart describing the size star nut needed compared to the Outside Diameter of the steering tube.
Chart ID of steering tube for Star Nut size
|Outside Diameter of Steerer Tube||Inside Diameter of Steerer Tube (STAR NUT SIZE)|
|25.4mm (1 inch)||22.2mm (7/8 inch)|
|28.6mm (1 1/8 inch)||25.4mm (1 inch)|
DIY MTB TIP: When tightening the threadless headset, the stem MUST be loose. The fastest way to damage or pull out the star nut is by tightening without a loose stem.
Selecting a Stem for Your Bike
Selection of a stem has to do with the function you’re trying to achieve with your bike. Generally, high angle stems are for an upright position.
Short stems are nice to improve handling and move a rider’s weight back for hill climbs.
A longer stem is used to shift weight forward, improving aerodynamics and slowly the steering sensitivity. A great example of this is how road bike riders want to cut the wind, bump very seldom make sharp turns like a mountain biker.
Best Bike Stem
For mountain bikes, RaceFace, Richey and Easton are the big brands. Here’s a link to a collection on Amazon to read more – Amazon MTB Stems
For mountain biking I recommend the RaceFace Respond. This is a forged stem from 6061 aluminum. High strength and fatigue resistance, plus it looks sweet. The four bolt clamp holds the handlebars securely. Pictured below, but here’s a link over to it on Amazon. RaceFace Respond
What is “Slamming” a stem
Slamming a stem is flipping the stem over so the angle of the stem is down versus up. This is a common practice for aggressive aerodynamic road biking.
What does a shorter stem do?
A shorter stem distance reduces the reach of the rider and makes the steering quicker. Longer stems position the rider in a weight forward position for more aggressive riding position.
What is the difference between Threadless vs Threaded Headsets?
The fastest way to recognize the difference between a threaded headset and threadless is that the threaded headset will have a big bolt under the stem.
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
David Humphries is the creator of DIY Mountain Bike. For me a relaxing day involves riding my mountain bike to decompress after a long day. When not on my bike I can be found wrenching on it or casting a fly on a small mountain stream. Read more about David HERE.